Part I and Part II of the WUI handbook provide fire engineering guidance to increase wildfire resiliency of an individual structure through a variety of design, construction, and maintenance considerations for building components, assemblies, and systems throughout the exterior envelope of a building, as well as selection, spatial layout, and maintenance of vegetative and non-vegetative fuels in the surrounding yard space or landscaping at building-/ parcel-scale. The intent is to limit the likelihood of damage or loss of an individual property to wildfires and/or structure-to-structure fire spread. Functionally, the handbook is primarily designed to support Fire Departments in assessing parcel-level WUI risk and providing mitigation guidance to homeowners The handbook centralizes the latest WUI fire research, science and engineering knowledge, and practice into one tool, while also supporting ongoing cooperation and collaboration between fire engineering/fire science and firefighting/fire service entities.

• Part I - Structural Hardening. This chapter provides a range of building construction features that can be implemented into the design of a new building or introduced as retrofits to existing buildings/homes to help limit structure ignition and total loss due to wildfires. These measures include various active and passive building features, elements, and systems from the top of structure down to the foundation (e.g., roof covering fire-rating, joint or interface detailing [See Figure A], vent protection).

• Part II - Defensible Space. This chapter provides guidance on the location, selection, and maintenance of vegetation and other combustible materials immediately surrounding a home or structure and the various means and methods to help slow or stop fire from spreading to the structure, causing ignition.

Note: While the focus of this handbook is primarily on residential construction, many of the wildfire safety requirements, guidance, and principles are conceptually relevant to commercial buildings and other structures in the built environment.

Note: The information and guidance in Part I and II are interrelated with key concepts and provisions at the neighborhood and community-scales. Thus, it is critical of users to be familiar with any practical constraints, existing conditions, limitations of community-scale services, and other underlying factors that may influence wildfire resiliency at the building/parcel-scale (e.g., limited access/egress, unreliable firefighting water supplies). There may be a need to enhance wildfire resiliency at the parcel-/building-scales to offset vulnerabilities of community-scale characteristics.

Note: This handbook is not intended to act as a code or standard, but a guidance document and reference tool. Codes referenced herein are the most recent editions at the time of development. Refer to the relevant jurisdiction(s) for adopted codes, standards, and local ordinances for statutory requirements.

• Systems Concept
  While Parts I and II of this Handbook provide guidance on individual components and features of the exterior envelope of a building and its immediate surroundings, an important concept to understand is that wildfire resiliency of a property relies on the system of interconnected and interrelated components. While each element, component, and assembly are critical, equally important is how each feature interacts with one another and must work together to reduce the chance of structure ignition. For the exterior envelope of the building, this may include paying special attention to how fire resistant the construction details are at joints (e.g., expansion joints, window-to-wall joints, wall-to-wall joints), interfaces of different building elements (wall-to-roof interfaces), edges, ridgelines, ventilation openings, etc. Protection of joints and interfaces is vital, as embers, flames and hot gases can enter a building via gaps between different building elements. For a building to be well protected, mitigation strategies must be applied holistically to ensure that the fire resistance, integrity, and continuity of the system of parts is maintained.

• Critical Items (for Retrofits)
  While structural hardening and defensible space guidance in the Handbook are important for reducing wildfire risk and should be provided for all new construction in high fire prone areas, most property owners with existing buildings or homes that pre-date WUI fire safety regulations will likely need to prioritize critical features on their property as retrofits. The following retrofits are considered critical for increasing wildfire resiliency of existing construction:
  
  
  1. Roof Construction & Covering - Upgrade roof covering to Class A. Refer to Section 1.1.1 Roof Construction & Covering Section for more details.
  2. Exterior Wall Construction & Cladding - Upgrade exterior cladding materials to noncombustible (e.g., stucco, masonry). For added fire resistance, provide a single layer of 5/8” Type X exterior rated gypsum below the cladding and weather seal. Refer to Section 1.3.1 Exterior Wall Construction & Cladding Section for details.
  3. Vent Protection (e.g., roof vents, soffit or under-eave vents, crawl space/basement vents) - Upgrade vents to those that are fire-rated/approved. Where infeasible, install corrosion-resistant metal mesh of maximum 1/8” (preferably 1/16”) to protect the vent. Refer to Sections 1.1.2 Roof Vents & Chimneys, 1.2.2 Soffit or Under-Eave Vents, and 1.2.1 Crawl Space/Basement Vents for more details.
  4. Window Protection - Upgrade windows to dual-paned with outer layer tempered glass and inner layer laminated. Ensure window framing is ignition-resistant, noncombustible or metal clad wood framing materials. Refer to Section 1.3.4 Windows for more details.
  5. Zones, Spacing, and Landscape Design (particularly Zones 0-1) - Pay special attention to keeping Zone 0 (0-5 ft) as a noncombustible zone, where plants and other man-made fuels are removed or minimized. Zone 0 should be provided around the entire home/building, including all combustible extensions (e.g., decks, balconies). Reduce vegetation density and move or remove combustible materials in accordance with guidelines and state/local requirements beyond 5 ft. Refer to Part II of the Handbook for more details.
  6. Roof Joints (e.g., roof panel-to-panel, around through-penetrations, roof-to-wall joint) and Wall Joints (e.g., head-of-wall to Roof, Bottom-of-Wall to Roof, around windows, doors, bottom-of-wall to foundation, wall-to-wall intersections) - Seal gaps within joints with fire-resistant caulk/sealant and protect gaps at interfaces with metal flashing. Refer to Sections 1.1.5 Roof Joints and 1.3.5 Joints for more details.
  
  

  Note while prioritizing the critical items indicated above should provide increased wildfire resiliency of an existing home or property, there's no guarantee that loss or damage will not occur in a major wildfire incident. Ongoing inspection and maintenance of the exterior of the home or property per the guidance in this Handbook provides the best odds of minimizing risk.

• Fire Resistance by Assembly - How to Inspect
  For several building construction components (e.g., walls, roofs, windows, doors), fire resistance is generally achieved by the build-up or assembly of many materials and components as a whole. For example, a Class A roof system may require the assembly of a Class A roof covering (e.g., asphalt single) with an underlying layer of gypsum product. However, in the field, a fire/wildfire safety inspector will likely be unable to verify if a Class A roof system is constructed appropriately to satisfy the “assembly” requirements to achieve fire resistance. This introduces some uncertainties into how a building component is constructed, as what can be seen on the outside may not be consistent with what's behind the surface. For example, some key through depth vulnerabilities includes combustible insulation, weather proofing, and combustible cavity materials. For increased certainty, property owners can refer to construction drawings or have a professional conduct small 'opening-up' works to verify construction.

• Importance of Flame Spread
  While fire-resistance of the materials and assemblies in the exterior envelope of a home, building or structure is important in reducing ignition risk, so is the vertical and lateral flame spread characteristics of those materials and systems. Flame spread is defined as “the propagation of flame over a surface” by the International Building Code. So, while a material or assembly may be able to resist fire and smoke from entering the building or home, if the exterior materials do not meet minimum flame spread requirements (e.g., a flame spread index of 25 or less when tested in accordance with ASTM E84 or UL 723), they may be providing a surface for fire to spread along the exterior envelope of the building, potentially igniting other building materials and other debris in more vulnerable parts of the structure, leading to fire spread into the interior of the home or building.

• Site Constraints
  Most urban and suburban homes cannot achieve 30 feet of setback to other structures or topographic hazards (e.g., steep slopes, ridge slides, drainages), let alone 100 feet of defensible space on all sides. Current wildfire building codes and referenced standards on structural hardening and defensible space do not provide requirements on how to achieve wildfire resiliency when various site constraints exist. These constraints can oftentimes introduce additional hazards (e.g., adjacent unmanaged vegetation, vacant lots, structure-to-structure fire spread, high intensity fire exposures due to topography) that are mostly outside of the control of the property owner. Some industry guidance does exist that recommends adopting “communal defensible space” concepts, enhancing defensible space requirements and/or structural hardening measures on the aspects of the buildings with limited setbacks and other site constraints [1]. However, this guidance is limited and does not necessarily address all forms of site constraints, construction typologies, vegetation conditions, and other practical limitations. Alternative methods, such as communal defensible space with neighbors and other structural hardening measures, are needed to address these increased risks. Some suggestions are provided in Part II for Defensible Space in the “Zones, Spacing, and Landscape Design” subsection and Part III for Neighborhood and Community-Scale Planning in the “Developing Siting” section.

• Fire Flow Pathways
  Fire can move across parcels via connecting “pathways” formed by combustible features such as vegetation, sheds, and fences. This is especially prevalent across linear features (e.g., fences, continuous path of surface fuels), which can carry fire between parcels [2]. While the most straightforward method of removing these pathways is to utilize noncombustible materials, there are a number of features where it is impossible to achieve this (such as vehicles) [2]. Refer to NIST Technical Note 2205 for more information [3].

• Multi-Hazard Considerations
  In locations where wildfire is a concern, there are typically other hazards which pose a risk as well. Residents and property owners need to make decisions about structures, vegetation, and other aspects of their parcel, while balancing consideration of multiple hazards and other objectives such as cost, aesthetics, and durability. Depending on the combination of relevant hazards, specific actions at the parcel-level may reduce the potential impacts of more than one hazard or the most effective action for one hazard may increase vulnerability to a different hazard. For example, ignition-resistant roofs can be designed to also help mitigate wind damage. On the other hand, some methods of fuels reduction (e.g., total removal of vegetation) may increase the likelihood or rate of slope erosion during flooding. The user of this handbook should be aware of how fire safety provisions, features, and assemblies might impact the effectiveness of mitigation for other hazards and performance criteria. Mitigations undertaken for one hazard should not exacerbate risk from another hazard.

Current, nationally recognized wildfire-specific building codes are generally nascent. Some key gaps in knowledge are detailed in the table below.

Retrofits or enhancements of new construction for wildfire resilience have cost implications. The following resources provide information on potential costs of various wildfire risk mitigations:

• Retrofitting a Home for Wildfire Resistance: https://headwaterseconomics.org/natural-hazards/retrofitting-home-wildfire-resistance/
• Construction Costs for a Wildfire-Resistant Home: California Edition: https://headwaterseconomics.org/natural-hazards/wildfire-resistant-costs-california/
• Building a Wildfire-Resistant Home: Codes and Costs https://headwaterseconomics.org/wildfire/homes-risk/building-costs-codes/

The main concerns associated with roofs, in general, are (1) the large surface area that can accumulate embers (and vegetative debris) and (2) the relative location and slope of the roof to proximate canopy fuels that can increase radiant exposure and direct flaming from crown fires. If the roof covering and overall roof assembly is of combustible materials, not fire rated, not well maintained, or littered with vegetative debris, then it is far more vulnerable to ignition from wildfire. The complexity of the roof shape will also play a key role in the likelihood of ignition [6]. Valleys, roof-to-wall intersections at split levels or dormers, joints, and other architectural embellishments on the roof can also support the collection of embers (“ember accumulation”) or vegetative debris that can lead to ignition. Additionally, as shingles age and curl, openings are exposed and may increase the number of places where embers can accumulate [7]. A study by Moore [8] concluded that out of 1,850 homes, 50% of the homes that ignited had wood roofs, while only 24% of homes that ignited had fire-resistant roofs. Within this study, fire-resistant roofs were considered as follows: Class A and B built-up assemblies, Class A and B prepared roofing, and properly installed Class C mineral surfaced asphalt shingles, asbestos cement shingles or sheets, concrete slabs, metal, slate shingles, fiber glass shingles, and clay or concrete tile [8].

• Roof Covering: The exterior roof cover or skin of a roof assembly comprised of a range of materials [6] (e.g., shingles, tiles, slate, metal panels, fiberglass asphalt shingles, bitumen membrane). According to the 2024 IBC, roof coverings are divided into Class A, B, and C, and must be tested in accordance with ASTM E108 or UL 790.

• Roof Assembly: An assembly of interacting roof components, including the roof deck, underlayment (comprised of a range of components such as vapor retarder, insulation, insulation cover boards, wood battens), and the roof covering [6].

• Asphalt Fiberglass Composition Shingles: Shingles composed of a fiberglass mat with asphalt and mineral overlay.

• Polyvinyl Chloride (PVC) Roofing: Thermoplastic roofing membrane typically used for buildings or structures with flat or low profiles and consisting commonly of 60 mil sheets with reinforced membranes. Seams are either hot-air heat welded, or chemical welded, and the membrane is either fully adhered, ballasted, or mechanically fastened.

• Thermoplastic Polyolefin (TPO) Roofing: Thermoplastic roofing membrane also used for buildings or structures with flat or low profiles. Sheets range from 40-100 mil, with reinforced or non-reinforced membranes, and installed fully adhered, mechanically fastened, or loose-laid with ballast. Seams are heat welded with hot air.

• Modified Bitumen (MB) Roofing: An asphalt-based membrane designed for buildings with low-slope or "flat" roof structures. MB roofing systems typically have five layers of protection (i.e., insulation, piles, MB membranes, adhesive or waterproofing material, surfacing).

• Fire Retardant Treated Wood (FRTW): According to the 2024 IBC, Section 2303.2, wood products that, when impregnated with chemicals by a pressure process or other means during manufacture, shall have, when tested in accordance with ASTM E84, UL 723, or ASTM E2768, a listed flame spread index of 25 or less (the flame front does not progress more than 10.5' (3200 mm) beyond the centerline of the burners at any time during the test which consists of a 30 minute exposure). Where used as roof coverings and evaluated following procedures in ASTM E108 / UL 790, FRTW must also be tested per weathering protocols such as ASTM D2898 [9]. Different test methods are often specified for other materials (e.g., plastic).

The fire resistance of roof assemblies to exterior fire exposures is defined by ASTM E108 or UL 790 Standard Test Methods for Fire Tests of Roof Coverings. The test method includes measurements of the surface spread of flame, the ability of the roof assembly to resist fire penetration from the exterior of the building to the inside, and the potential for the roof covering to generate flying brands (i.e., embers) from the burning roof covering [10].

Note: Some roof coverings rely on an underlying material, or special installation techniques, to improve their fire rating [12]. These types of roofs are considered fire-rated roof assemblies. An example of a fire-rated roof assembly are fire-retardant treated wood shakes, aluminum and recycled plastic and rubber roof coverings. Examples of underlayment materials include a mineral surfaced cap sheet (formerly referred to as a Type 72 cap sheet) adequate to provide Class A membrane construction, and a fiberglass gypsum panel [12] with a thickness adequate for passing the ASTM E108/UL 790 test.

• ASTM E84 Standard Test Method for Surface Burning Characteristics of Building Materials: https://www.astm.org/e0084-21a.html
• ASTM E108 Standard Test Methods for Fire Tests of Roof Coverings: https://www.astm.org/e0108-20a.html
• UL 723 Test for Surface Burning Characteristics of Building Materials: https://www.shopulstandards.com/ProductDetail.aspx?UniqueKey=34224
• UL 790 Standard Test Methods for Fire Tests of Roof Coverings: https://standardscatalog.ul.com/ProductDetail.aspx?productId=UL790
• ASTM C1177 Standard Specification for Glass Mat Gypsum Substrate for Use as Sheathing: https://www.astm.org/c1177_c1177m-17.html
• ASTM D2898 Standard Practice for Accelerated Weathering of Fire-Retardant-Treated Wood for Fire Testing: https://www.astm.org/d2898-10r17.html
• ASTM D3909 Standard Specification for Asphalt Roll Roofing (Glass Felt) Surfaced with Mineral Granules: https://www.astm.org/d3909_d3909m-14r21.html

• 2024 International Wildland-Urban Interface (IWUI) Code:
  • Section 504.2, 505.2, 506.2 Roof Assembly.
  • Section 507 Replacement or Repair of Roof Coverings.
• 2022 California Building Code (CBC): Section 705A.2 Roof Coverings.
• 2022 NFPA 1140 Standard for Wildland Fire Protection: Section 25.3 Roof Design and Materials.

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for any additional requirements.
• Check local general plan, comprehensive plan, multi-hazard mitigation plan or zoning documents for any additional requirements.
• International Residential Code (IRC) (if applicable - check for wildfire amendments).

• Replace any damaged, broken, or missing pieces or sections.
• Remove litter and other vegetation debris on roof annually before core fire season. Check underneath roof tiles near eaves or under ridge caps [15].
• Replace roof with Class A rated roofing material. Note: Class A covering alone is not enough; the entire roof system should be considered to include underlayment and any other components that impact wildfire vulnerability.
• For tile roofs, bird-stop or mortar open ends of tiles at the roof eaves, roof edge, hips, and ridges to reduce vulnerability to ember intrusion and ignition [6].
• For tile roofs, install non-corrosive metal flashing under tiles at roof valleys. For profiled tile, lead or flexible flashing should be installed (as recommended by the manufacturer).
• Replace roof coverings before significant deterioration occurs due to exposure to weathering.
• Replace any exposed combustible foam with noncombustible insulation [6].

• Wildfire testing does not currently account for weathering of materials prior to fire exposure. This is of particular concern for FRT shakes and shingles.
• ASTM E108 and UL 790 are an exterior fire exposure based on a piloted ignition scenario of “in-plane” roof coverings or assemblies. This may not be reflective of anticipated fire exposures for wildfire conditions (e.g., embers, large radiative exposure from wildfire flaming, direct flame impingement, heat release rates characteristic of wildfires). Test conditions can oftentimes be less severe than actual wildfire exposures that are in uncontrolled environments. In addition, ASTM E108/UL790 do not test edge of roof conditions, which is a key vulnerability.
• In some cases, it may be challenging to verify in-the-field if a roof assembly is rated to Class A, B, or C, as the listing is often not visible when installed and “opening-up” the assembly to verify through depth construction is generally not feasible. (Professional judgement and local knowledge of construction practices may be required to have confidence in “assembly” construction details.)
• Additional training is needed for inspectors to accurately identify roof coverings as Class A, B, or C.
• Additional training is also needed to provide field inspectors or property owners with an understanding of the limitations of current fire tests standards (e.g., ASTM E108 and UL 790 do not test roof edge conditions).

• Insurance Institute for Business & Home Safety (IBHS)
  • Ember Testing - https://ibhs.org/wildfire/building-vulnerability-to-ember-exposure/
  • HOME Preparedness - https://disastersafety.org/wp-content/uploads/2021/08/WFR-Home-Preparedness-Guide.pdf
• National Fire Protection Association (NFPA)
  • Firewise - https://www.nfpa.org/-/media/Files/Firewise/Fact-sheets/FirewiseFactSheetsRoofingMaterials.ashx
• Federal Emergency Management Agency (FEMA)
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Roof - https://ucanr.edu/sites/fire/Prepare/Building/Roof/
• Headwaters Economics
  • Building a Wildfire-Resistant Home: Codes and Costs - Headwaters Economics - Building a Wildfire-Resistant Home: Codes and Costs https://headwaterseconomics.org/wp-content/uploads/building-costs-codes-report.pdf

The intrusion of embers and flames via vents can be a major source of structure ignition during a wildfire [16], [17], [18], [19]. The main concern with roof vents is that they oftentimes introduce openings through the exterior envelope of a building where windborne embers, flames, or hot gases from wildfires or fires from surrounding landscaping and structures can enter the building, which can lead to ignition of interior contents and other combustible building materials. Both inlet and outlet vents, especially on the windward side of the building, are sources of ignition vulnerability, as fire behavior can create reverse flows due to over-pressures that can drive embers, flames, and hot gases into a building interior (e.g., attic, interstitial spaces). Chimneys, on the other hand, can provide a potential source for embers to travel from a fireplace to outside the structure, potentially causing a wildfire. Furthermore, roof vents and chimneys introduce numerous joints and surfaces where vegetative debris can accumulate around the vent perimeter, opening, or at the chimney chase, providing a source of combustible fuels for ignition.

• Chimney: A primarily vertical structure containing one or more flues, for the purpose of carrying gaseous products of combustion and air from a fuel-burning appliance to the outdoor atmosphere [9].

• Gas Fireplace Chimney: A vertical or horizontal vent designed to release hot air from a gas burning fireplace to the outdoor atmosphere.

• Ember (also known as fireband): Smoldering or flaming particles of vegetation from tree branches, pieces of chaparral shrubs, or other combustibles (such as construction materials and furnishings in structures) that ignite and burn during a wildfire and are carried by winds in front of the wildfire [20].

• Gable-end Vent: A vent located in the gable-end wall, just below the roof ridge to allow flow into and out of attics. Gable-end vents normally have louver blades. This type of vent is commonly metal and normally has an insect screen [6].

• Hip Vent and Ridge Vent: A continuous vent installed along the full length of the hip or ridge of a roof, with the air slots underneath the hip or ridge vents located only at the top portion of the hip or ridge. These vents are typically comprised of metal or plastic and may have internal or external baffle media to minimize the entrance of wind-driven rain or snow [6], [13].

• Mechanical Exhaust Vents (Whirly birds, Wind Turbines): Cylindrical dome-shaped vents that sit on the roof of a building and spin in the wind, creating a vacuum that extracts warm air and moisture from the attic. Turbines sit higher above the roof surface, so they stand out more than other exhaust options, but they move air effectively. When there's no wind, their function is similar to that of a static exhaust vent [21].

• Powered Exhaust Vent: These types of vents are powered by electric, solar or a combination of both and are either roof-mounted or gable-mounted. Powered vents typically include thermostat control to provide optimum airflow rating.

• Spark Arrestor Cap: A metal assembly at the top of the chimney that prevents embers from leaving the chimney while also preventing embers from entering the chimney in the event of a wildfire.

• Through-roof Vent: A vent that penetrates the roof to allow exfiltration of attic air or connection to an HVAC system. They can also be known as a dormer or eyebrow vent, depending on the shape of the housing. These types of vents are typically comprised of metal, plastic, or rigid fiberglass.

• Off-Ridge Vent: A vent located just below a roof's ridge. These vents are typically comprised of plastic or metal and may have internal or external baffle media to minimize the entrance of wind-driven rain or snow.

• Vent: A device or assembly placed in an exterior opening of a building (located in an eave, gable, wall, or foundation) that allows for aeration (free exchange of air) for temperature and moisture control, particularly for unconditioned spaces [16].

Wall mounted and under-eave vents - The ember and direct flame impingement resistance of gable-end, crawl space, other wall-mounted vents and under eave area vents are defined by ASTM E2886 Standard Test Method for Evaluating the Ability of Exterior Vents to Resist the Entry of Embers and Direct Flame Impingement. This test standard prescribes two individual methods to evaluate the ability of the vent to resist: (1) the entry of embers and (2) flame intrusion. Full-scale tests at IBHS demonstrated that ASTM E2886-compliant vents limit the entry of large embers, and that the embers collected behind these vents (e.g., on the attic side) were small and incapable of igniting combustibles [22]. Note: ASTM E2886 does not provide explicit quantitative acceptance criteria for ember intrusion or flame intrusion. However, ember intrusion is evaluated based on observation of occurrence of combustion of a cotton pad on the unexposed side of the vent given a 3-min exposure to tumbled Class C brands. Performance criteria for the 10-min flame intrusion test as well as integrity test are specified in ASTM E2912. Visual observations are made for the presence and duration of any flame penetration through the vent.

ASTM E2912 assesses the ability of non-mechanical fire dampers used in vented construction in its open state to limit passage of hot gases, radiation, and flames. Roof ridge, off-ridge (field) and all other non-wall mounted roof vents are not included in the scope of this standard. Acceptance criteria are typically not provided in ASTM standards, including this one [16]. Acceptance criteria are specified in the California Building Code (CBC), Section 706A.2 and NFPA 1140 Section 25.3.3.

All other roof vents - Currently there are no standard fire tests to evaluate ember intrusion and impact of direct flame impingement on non-wall mounted roof vents (e.g., roof ridge or hip vents, off-ridge vents, mechanical exhaust vents, powered exhaust vents, through-roof vents).

Note: Gable end and other wall-mounted vents that have been included in a roof assembly tested per ASTM E108 to achieve a Class A rating have only been tested for whether they contribute to flame spread, fail, detach from the roof or produce embers. ASTM E108 does not assess if a vent can resist the penetration of embers or direct flames from wildfires. The vents would still need to be tested per ASTM E2886.

Factory-built chimneys and fireplaces - Chimneys and fireplaces should be fire-blocked in accordance with UL 103 and UL 127 (Required for factory-built chimneys and fireplaces in 2024 IBC, Section 718.2.5.1).

• ASTM E2886/E2886M-14 Standard Test Method for Evaluating the ability of Exterior Vents to Resist the Entry of Embers and Direct Flame Impingement: https://www.astm.org/e2886_e2886m-20.html
• ASTM E2912 Standard Test Method for Fire Test of Non-Mechanical Fire Dampers Used in Vented Construction: https://www.astm.org/e2912-17.html
• UL 103 Factory-Built Chimneys for Residential Type and Building Heating Appliances: https://www.shopulstandards.com/ProductDetail.aspx?UniqueKey=21968
• UL 127 Standard for Factory-Built Fireplaces: https://www.shopulstandards.com/ProductDetail.aspx?UniqueKey=22727

• 2024 International Wildland-Urban Interface (IWUI) Code:
  • Section 504.10 Vents
  • Section 605 Spark Arresters
• 2022 California Building Code (CBC):
  • Section 706A Vents
  • Section 718.2.5.1 Factory-Built Chimneys
• 2022 NFPA 1140 Standard Wildland Fire Protection:
  • Section 25.3.3 Vent Assemblies
  • Section 25.8 Chimneys and Flues

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local planning documents such as general or comprehensive plans, multi-hazard mitigation plan, zoning maps.
• International Residential Code (if applicable - check for wildfire amendments).

• Debris should be removed from around vents and chimney chases periodically, and at a minimum before fire season.
  • Wind-blown vegetative debris must be removed from the inlet of all ridge- and off-ridge vents, paying particular attention to vents with plastic components as these materials are commonly used in ridge vents [24].
• Provide ember resistant vents protected with corrosion-resistant wire mesh with openings no larger than 1/8”, preferably 1/16”.
  • Common 1/4” screens are ineffective and should be replaced [24].
  • Do not use plastic-clad fiberglass mesh as they can melt and burn [24].
• Provide spark arrestor cap on all chimneys.
  • Chimneys serving fireplaces, barbecues, incinerators, or decorative heating appliances in which solid fuel is used, should be provided with a spark arrester [25].
  • Spark arrestors are required to be constructed of woven or welded wire screening of 12 USA standard gage wire having openings not exceeding 1/2” [25].
• Chimney outlets should have at least 10' of clearance to vegetation and other obstructions [26].
• Avoid using off-ridge and ridge vents that have not been tested against ASTM E2886. Of the ridge and off-ridge outlet vent options, the following performed well [19]:
  • Miami-Dade wind-driven-rain-compliant ridge vent.
  • Turbine (off-ridge) vent with screening attached to the roof sheathing.
• Replace non-metal roof vents with corrosion-resistant metal vents and vent flashing.
• Ensure turbines can spin freely to minimize ember intrusion into the attic.
• Specify and install vent openings with a maximum net free area of 144 in² [6].
• Place all vent openings at least 10' from other buildings or property lines to avoid ignition from embers and hot gases from an adjacent building that has ignited [6].
• Ember and flame-resistant vents that have been tested and approved for use are available and listed. A sample list of compliant products can be found on the California Office of the State Fire Marshal, Building Materials Listing Program website. Other databases of listed products are not yet available.
• Do not block or cover any existing vent before considering whether its removal will hamper the flow of ventilation [15].
• Dryer vents should have a noncombustible louver or flap [22].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Vent fire testing does not account for weathering of materials prior to fire exposure or the impact of general wildfire environmental conditions (e.g., high winds, flying debris, impact from objects).
• ASTM E2886 does not evaluate the ability of vents to completely exclude entry of flames or embers, nor does it test for transmission of smoke or hot gases.
• ASTM E2886 does not include roof ridge and off-ridge (field) vents. Thus, there is no accepted procedure to evaluate ember intrusion and direct flame impingement of ridge and off-ridge vents. However, the functional parts of some approved vents have been installed in dormer-style off-ridge vents and should perform as well in this location as others.
• In most instances, it is challenging to verify, in-the-field, if an off-ridge vent has been fire-tested. (Professional judgement and discussion with the homeowner are required.) Training may be required to be able to identify fire-tested foundation vents and under-eave vents.
• Air flow calculations may need to be reconsidered or redesigned where fire rated vents are installed in existing structures, to ensure code required airflow is satisfied.

• Insurance Institute for Business & Home Safety (IBHS)
  • Ember Testing - https://ibhs.org/wildfire/building-vulnerability-to-ember-exposure/
  • Vulnerability of Vents - https://ibhs.org/wp-content/uploads/wpmembers/files/Vulnerability-of-Vents-to-Wind-Blown-Embers_IBHS.pdf
  • Ember Media - https://www.facebook.com/watch/?v=389602881106017
  • Preparedness - https://disastersafety.org/wp-content/uploads/2021/08/WFR-Home-Preparedness-Guide.pdf
• National Fire Protection Association (NFPA)
  • Firewise - https://www.nfpa.org/-/media/Files/Firewise/Fact-sheets/FirewiseFactSheetsAtticsCrawlSpaces.ashx
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones, Technical Fact Sheet No. 8 - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf
  • Wildfire Resilient Detailing, Joint Systems, and Interfaces of Residential Building Components: https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-detailing-joints.pdf
• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Vents - https://ucanr.edu/sites/fire/Prepare/Building/Vents/
• California Office of the State Fire Marshal
  • Building Materials Listing - https://osfm.fire.ca.gov/what-we-do/fire-engineering-and-investigations/building-materials-listing

Similar to other “penetrations” through the plane of the roof, skylights present a number of potential vulnerabilities that could result in the ignition of the home during a wildfire, including: (1) direct opening to the interior of the building when operable skylights are left open, (2) depending on the construction materials of the skylight (such as skylights containing plastic glazing materials) may be of non-fire rated or combustible materials and (3) the roof-to-skylight junction can be a location for the accumulation of vegetative debris and, when a wildfire threatens, embers.

• During a wildfire incident, skylights if left open can provide a direct pathway for embers and/or hot gases to enter the interior space of the building and result in the ignition of internal furnishings.

• Skylights can be constructed of a range of combustible (e.g., plastic) and noncombustible materials (double pane glazing, tempered and laminated glazing), many of which can be compromised due to effects of radiant heat exposure and direct flame contact. Note however, that newer skylights typically consist of an outer pane of tempered glass and an inner pane of laminated glass. This provides a degree of protection from radiant heat exposure and direct flame contact. In these scenarios, debris accumulation is the more prominent concern.

• Skylights also create receptive surfaces and joints where vegetative debris can collect and subsequently be ignited from embers on top or next to the skylight framing. Vegetative debris and embers can more easily accumulate on low-sloped roof skylights creating potential hotspots [7]. Typical temperatures of these potential fire sources would be high enough to break tempered glass [27]. Most guidance recommends using a flat glass skylight rather than a plastic dome style because the plastic is combustible or will melt and allow for embers to enter the interior building space. However, there are situations based on the slope of the roof where flat glass could become more vulnerable [27]. A dual-pane skylight consisting of an outer pane of tempered glass and an inner pane of laminated glass will provide the best protection.

• Unit Skylight: A factory-assembled, glazed, fenestration unit, containing one panel of glazing material that allows for natural lighting through an opening in the roof assembly while preserving the weather-resistant barrier of the roof [28].

• Skylights and Sloped Glazing: Glass or other transparent or translucent glazing material installed at a slope of 15 degrees or more from vertical. Unit skylights, tubular daylighting devices, glazing materials, solariums, sunrooms, roofs, and sloped walls are included in this definition [28].

• Laminated Glazing: An assembly consisting of two or more lites of glass bonded together by an interlayer [29].

• Tempered Glazing: General term for glass that has been subjected to a thermal treatment characterized by rapid cooling to produce a compressively stressed surface layer (includes fully tempered glass and heat-strengthened glass) [29].

Skylights can comply with several different requirements to resist the effects of fire. Applicable options are as follows [30], [31]:

• Be constructed of multi-pane glazing with a tempered pane.
• Be constructed of glass block units.
• Be comprised of fire-resistance rated glazing assembly per ASTM E119.
• Have a fire-resistance rating of not less than 20 minutes when tested in accordance with NFPA 257 or ASTM E119.

• ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials: https://www.astm.org/e0119-20.html
• NFPA 257 Standard on Fire Test for Window and Glass Block Assemblies: https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=257
• SFM Standard 12-7A-2 Exterior Windows

• 2024 International Wildland-Urban Interface (IWUI) Code: Sections 504.8, 505.8 Exterior Glazing
• 2022 California Building Code (CBC):
  • 202 Definitions
  • 708A Exterior Windows, Skylights, and Doors
• 2022 NFPA 1140 Standard for Wildland Fire Protection: 25.7 Exterior Openings

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Ensure operable skylights are closed prior to leaving a property located in high fire prone areas.
• If “glass-type“ skylights are specified, provide tempered glass for the outer pane and laminated glass for the inner pane.
• Regularly inspect the roof for vegetative debris accumulation on and around skylights. For all skylight types, debris can accumulate at roof-to-skylight intersections. If ignited by embers, flames can potentially wrap around and impinge upon the top surface of the skylight Debris is more likely to accumulate on top of a skylight installed on a flat roof [32].
• If plastic skylights are installed, it is recommended that they are replaced with double paned glazing units with outer pane as tempered glass and inner pane as laminated, or insulated glazing units. Glazing products that are wired glass and/or FM Approved are also acceptable where the use of tempered-laminated glass is not feasible [11]. Glazing products that are not recommended are single pane of annealed glass or plastic glazing [6].
• If skylight opens, install non-corrosive metal screening with openings at least 1/8” (1/16” preferred) [3].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• National Fire Protection Association (NFPA) and the Insurance Institute for Business & Home Safety (IBHS)
  • Firewise Wildfire Research Fact Sheet on Skylights - https://www.nfpa.org/education-and-research/wildfire/firewise-usa/firewise-usa-resources
• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Skylights - https://ucanr.edu/sites/Wildfire/Roof/Skylights/
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones, Technical Fact Sheet No. 10 - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf

Residential solar panel installations are a relatively new technology and building component/feature that has evolved significantly since 2014. While there have been significant strides in understanding fire hazards and risks from these systems and how to effectively design to mitigate those risks, little research and design standards have been undertaken to specifically address wildfire exposures and the associated risks that contribute to home ignition, fire load, or firefighter safety during wildfire operations for these systems.

General concerns include:

• Rooftop placement is isolated from routine occupant awareness, fixed fire protection systems, and detection features. These factors result in potential accumulation of debris, delayed fire detection, and no fire protection.

• Combustible portions of the module and other components provide fuel to support a fire and can reflect heat from a fire towards the roof, contributing to combustion and burn-rate.

• Defensive fire service actions have been found to have reduced impact because photovoltaic (PV) panels conceal and shield fire below. Fire service must take additional precautions when approaching a structure that includes rooftop solar installation, as power generated by the panels cannot be turned off. Fire service may not identify presence of PV panels if not visible from ground-level.

• In general, there is limited data on how PV systems behave under wildfire exposure. There is potential for these systems to contribute to a wildfire event during substantial exposure, based on the materials used and their constant energization when exposed to light.

• Rooftop PV systems may include penetrations for building service which may compromise the continuity and integrity of the building envelope, potentially leading to early failure during wildfire exposure.

• Photovoltaic (PV) Module: An environmentally protected planar assembly of solar cells, optics, and ancillary parts, such as interconnections, terminals, (and protective devices such as diodes) intended to generate direct current power under unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate) [33].

• PV Panel: This is the technical term for a solar panel, often used interchangeably with PV module (especially in one-module systems), but more accurately used to refer to a physically connected collection of modules (i.e., a laminate string of modules used to achieve a required voltage and current). A collection of photo-voltaic modules mechanically fastened together, wired, and designed to provide a field-installable unit [33].

• PV System: A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array, rack support system, and balance of system components [33].

• Photovoltaic-Thermal (PV/T) System: A photovoltaic system that, in addition to converting sunlight into electricity, collects residual heat energy and delivers both heat and electricity in usable form. Also called a total energy system or solar thermal system.

• Solar Panel: Synonymous with PV panel.

PV systems (PV modules with mounting systems) are available with Class A, B, and C ratings. Classification of roof mounted PV systems is based on UL 1703 and 61730 (PV Modules, legacy US standard and update to international standard) as well as UL 2703 (PV mounting systems). The combination of roof mounted solar modules and racking components is required to be considered as a system. The system is required to meet or exceed the fire classification of the roof assembly on which they are mounted. PV modules are also categorized by roof slopes they are tested for.

Module classification under UL 1703 is still supported, but eventually will be withdrawn in favor of the updated UL 61730. UL 1703 and 61730 assign module types that are based on panel material/thickness, encapsulation method, substrate material/thickness, frame, and fire test performance for external fire exposure.

There are currently no fire test standards for solar panels exposure to wildfires. The following are closely related fire test standards for roof mounted PV systems. If solar panels are integral with the roof covering, then they must comply with ASTM E108.

• ASTM E108 Standard Test Methods for Fire Tests of Roof Coverings: https://www.astm.org/e0108-20a.html
• UL 790 Fire Test of Roof Coverings: https://standardscatalog.ul.com/ProductDetail.aspx?productId=UL790
• UL 1703 Standard for Flat-Plate Photovoltaic Modules and Panels: https://standardscatalog.ul.com/ProductDetail.aspx?productId=UL1703
• UL 61730-1 and UL 61730-2 Photovoltaic (PV) Module Safety Qualification - Part 1: Requirements for Construction and Part 2: Requirements for Testing: https://www.shopulstandards.com/ProductDetail.aspx?UniqueKey=43587, https://www.shopulstandards.com/ProductDetail.aspx?productId=UL61730-2_2_S_20221028
• UL 2703 Mounting Systems, Mounting Devices, Clamping/Retention Devices, and Ground Lugs for Use with Flat-Plate Photovoltaic Modules and Panels: https://standardscatalog.ul.com/ProductDetail.aspx?productId=UL2703
• ASTM E2908 Standard Guide for Fire Prevention for Photovoltaic Panels, Modules, and Systems: https://www.astm.org/e2908-12r18.html

There are currently no building codes or standards for solar panels exposed to wildfires. However, the following codes and standards are closely related.

• 2024 International Wildland-Urban Interface (IWUI) Code: Section 504.2, 505.2 Roof Assembly
• 2022 California Building Code (CBC): Chapter 7A, Section 705A.2 Roof Coverings, Section 3111 Solar Energy Systems
• 2022 NFPA 1140 Standard for Wildland Fire Protection:: Section 25.3 Roof Design and Materials

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Install Class A rated PV panels for the greatest protection.
• Maintain the panels free of debris and damage. This includes providing sufficient clearance between the panels and roof for clearing debris and inspecting the underside for damage.
• Install invertor and energy storage components within the building to minimize ignition hazards. These elements should not be installed outside within 5' of exterior walls.
• Where permitted by the local authority having jurisdiction and manufacturer, install mesh enclosures (also referred to as mesh guards) to protect the underside of the panel systems. These are typically intended to keep birds and rodents away from the panel systems, however, can also help to prevent debris accumulation, when regularly maintained.
• Improper design, installation or components can cause hot spots and/or electrical failures that can lead to ignition of the system and adjacent materials during high load. Self-installed systems can significantly increase the risk of fire. PV system installation must be appropriately designed and installed using classified and listed products. Compliant PV systems have a very low incident rate of ignition.
• Roof attachments and methods must be compatible with the roof system and use appropriate precautions. Incorrect attachment methods can compromise fire performance, waterproofing ability, and in extreme cases, structural performance.

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• There is limited information available on how solar panels behave in a wildfire event, as this is dependent on the module, mounting hardware and roof as a system. Actual performance of a rack-mounted PV system exposed to fire or flame is strongly dependent on the mounting geometry of the PV array and properties of the components that make up the specific PV module type [34].
• Fire classification requirements were updated in 2014 (UL 1703) and later updated for international standard consistency (UL 61730) with substantial focus on fire performance considerations. Since PV systems continue to be an innovative field, technology and requirements will continue to evolve.
• Battery and inverter equipment locations do not typically consider exterior exposure risks and may be located on the building exterior.

• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
• Fire Safety Journal
  • “Experimental Study of Flame Spread Underneath PV Panels” - https://doi.org/10.1016/j.firesaf.2020.103027
• Solar ABCs / UL
  • Fire Classification Rating Testing of Stand-Off Mounted Photovoltaic Modules and Systems - http://www.solarabcs.org/about/publications/reports/flammability-testing/pdfs/SolarABCs-36-2013-1.pdf
  • Flammability Testing of Standard Roofing Projects - http://www.solarabcs.org/about/publications/reports/flammability-testing/pdfs/Flammability_Interimreport.pdf
• National Fire Protection Association (NFPA)
  • Development of Fire Mitigation Solutions for PV Systems Installed on Building Roofs Phase 1 - https://www.nfpa.org/News-and-Research/Data-research-and-tools/Electrical/Development-of-Fire-Mitigations-Solutions-for-PV-Systems-Installed-on-Building-Roofs-Phase-1
  • Property Insurance Research Group Forum on PV Panel Fire Risk - https://www.nfpa.org/News-and-Research/Data-research-and-tools/Proceedings/Property-Insurance-Research-Group-Forum-on-PV-Panel-Fire-Risk
  • Photovoltaic and Energy Storage Systems Online Training Series - https://www.nfpa.org/News-and-Research/Resources/Emergency-Responders/High-risk-hazards/Photovoltaics-Systems

In general, joints create gaps in the continuity of a fire rated or fire resistive roof assembly, presenting a potential avenue for embers, hot gases, or flame to breach the exterior roof envelope. Joints can also create places for the accumulation of combustible debris that can be easily ignited by embers, hot gases, or direct flaming, or where embers collect and create a concentrated source of heat. Both scenarios can potentially lead to ignition of the roof underlayment or other combustible interstitial spaces at the joints. Overtime, the size and/or condition of joints may also change from expansion, contraction, and general wear-and-tear due to moisture, freeze-thaw cycles, temperature gradients and other weathering. This can further create potential pathways for ignition, potentially short-circuiting the fire resistance provided by a Class A roof assembly [15]. Unfortunately, there is currently no wildfire-specific fire test for roof joint protection systems or products. Note: One practical challenge with roof joints is that they may not be visible (e.g., between panel joints on the roof deck) or easily accessible, therefore making it difficult to verify if appropriate joint protection is provided.

• Joint: An opening in or interface between adjacent assemblies or building components that is created to accommodate building construction tolerances or movements due to thermal, seismic, wind, or any other loadings [35].

• Fire-Resistant Joint System: An assemblage of specific materials or products that are designed and tested in accordance with a standard fire test to resist, for a prescribed period of time, the passage of fire through joints made in or between fire-resistance rated assemblies [35]. (Note: There are currently no fire-resistant joint system tests for wildfire exposures.)

• Roof Ridge: The roof ridge, or ridge of a roof is the horizontal line running the length of the roof where the two roof planes meet. This intersection creates the highest point on a roof, sometimes referred to as the peak [36].

• Roof Valley: A roof valley is formed where two roof slopes or planes meet. A valley occurs where two roof planes intersect. Valleys are places where leaves and needles often accumulate and where embers can land [12].

• Flashing: A thin metal that is installed at joints to protect against intrusion of unwanted elements such as water and embers.

• Expansion Joint: A physical discontinuity that spans the entire breadth of an element in a building, creating two separate sections of the element instead of one bigger one. They are designed and configured to allow the different building sections to move independently of each other, so the structures don't become overstressed and crack or break under various loads (e.g., thermal expansion/contraction, moisture-related dimensional change, seismic movement) [37].

• Through Penetration: A breach in both sides of a roof, floor, floor-ceiling, or wall assembly to accommodate an item passing through the breaches (Definition adapted from 2022 CBC) [14].

Currently, there is no fire test standard for joint systems that exist throughout the exterior envelope of a building to evaluate fire performance to ember intrusion, direct flame impingement, or thermal transmission of heat from wildfires. Fire rated joints are necessary to maintain a roof system's fire rating, integrity, and continuity to wildfire exposure. While a variety of fire tests exist for joints for interior building fire exposures (e.g., ASTM E1966 or UL 2079), none are explicitly designed for exterior fire exposures such as wildfires in combination with weathering. A range of joint systems (e.g., static joints, movement joints, roof expansion joints) and building component interfaces (e.g., chimney-to-roof, vent-to-roof, skylight-to-roof, roof panel-to-roof panel, edge-of-roof joint, roof-to-wall) for exterior wildfire exposures are still needed.

Currently, there is no fire test standard for joint systems (roof joints or otherwise) to evaluate fire performance to ember intrusion, direct flame impingement or thermal transmission of heat from wildfires.

• 2024 International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC): No explicit requirements
• 2022 NFPA 1140 Standard for Wildland Fire Protection: No explicit requirements

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Debris should be removed from around all joints created at the roof (e.g., expansion joints, vents/chimney-to-roof joints).
• Noncombustible materials (e.g., compressed mineral wool) in lieu of combustible materials should be provided to fill expansion joints.
• Fire-resistant sealants should be provided in lieu of non-fire rated caulking.
• Metal flashing should be installed at vent-, chimney-, and skylight-roof joints to limit ember penetration or spot fires from ignited roof debris from penetrating into the roof substrate. Where the roof underlayment is combustible, refer to appropriate protection measures in the roof construction/covering section for detailing.
• For new construction, limit the number of joints and elevation changes in the roof design [38].
• Where apparent, seal small gaps between the roof and any roof penetrations with appropriate joining strips (silicone recommended). Do not use polymer joining strips unless fire rated [15].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Currently, there is no fire test standard for joint systems (roof joints or otherwise) to evaluate fire performance to ember intrusion, direct flame impingement, or thermal transmission of heat from wildfires.
• It is unclear how susceptible various roof-joints are to wildfire exposures.

• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Roof - https://ucanr.edu/sites/fire/Prepare/Building/Roof/
• Federal Emergency Management Agency (FEMA)
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf
  • Wildfire Resilient Detailing, Joint Systems, and Interfaces of Residential Building Components - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-detailing-joints.pdf
• General Roof Expansion Joint References
  • National Research Council (NRC) - Built-up Roof joints - https://nrc-publications.canada.ca/eng/view/ft/?id=ccde0331-086c-41a9-8fff-7b82e29f8144
  • Brick Industry Association - Brick Join - https://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/18a-accommodating-expansion-of-brickwork.pdf
  • Copper Development Association - Roof-to-Wall - https://www.copper.org/applications/architecture/arch_dhb/arch-details/building_expansion/roof_edges.html
  • AISC - Basic construction details (Non-Fire) - https://www.aisc.org/globalassets/modern-steel/archives/2005/04/2005v04_expansion_joints.pdf

The roof edge is a portion of a structure that is highly vulnerable to ignition due to (1) proximity to gutter systems and associated vegetative debris, (2) openings or breaches in the continuity of roof construction along the edges, and (3) proximity to trees, plants, and other man-made fuels surrounding the structure (e.g., wood piles, tool, or storage shed). Most gutter systems are located at the roof edge. As described in the gutter section, these building elements can collect vegetative debris, when not protected with a gutter guard or cleared out regularly. In the event of a wildfire, this vegetative debris will be a receptive fuel bed for embers, creating a localized fire hazard near the roof edge. In addition, roof edges are also typically sources of breaches in the continuity of roof assemblies, as roof edges may not be fully encapsulated. That is, the roof edge can have gaps between the roof covering and underlayment, which create a source of weakness for embers and flames (from ember ignited vegetative debris) to enter the combustible substructure of the roof. Roof edges can also be exposed to direct flame impingement and high temperatures where surrounding vegetation and other man-made fuels come into close proximity or directly touch the roof edge.

• Metal Drip Edge: Metal flashing installed at the edge of the roof designed to keep water or embers away from the fascia board and roof sheathing.

• Fascia or Gutter Boards: Vertical roof trim located along the perimeter of a building, usually below the roof level, to cover the rafter tails at the eaves and to seal off the top of the siding along the rake [36].

Currently, there are no fire rated assemblies for roof edge detailing. However, several strategies for mitigation exist (see Table 11).

Currently, there is no fire test standard for edge of roof detailing to evaluate fire performance to ember intrusion, direct flame impingement, or thermal transmission of heat from wildfires.

• 2024 International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC): 705A.2 Roofing
• 2022 NFPA 1140 Standard for Wildland Fire Protection: 25.3.7 Roof Design and Materials

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Install a metal drip edge or flashing at the roof edge to minimize ember entry to the roof underlayment via materials burning in a rain gutter or wind-blown embers impinging on the area at the edge of the roof [12].
• Replace any damaged, broken, or missing pieces or sections of roof at the roof edge.
• Remove litter and other vegetation debris at the roof edge and in gutters as needed.
• For profiled tile roofs, bird-stop or mortar open ends of tiles at the roof edges to reduce vulnerability to ember ignition.
• For tile roofs, install corrosion-resistant metal flashing under tiles at roof edge. A cap sheet should be installed under the metal flashing.
• For profiled tile, lead or flexible flashing can be installed (as recommended by the manufacturer) [6]. Where underlayment is combustible provide an additional fire-resistant layer (e.g., gypsum board, mineral fiber, glass fiber, or other approved materials) between the roof covering and underlayment.
• Replace roof coverings and underlayment at roof edge before significant deterioration with age and exposure to weathering.
• Trim back vegetation touching, overhanging, or in close proximity to the roof edge (i.e., within 10 feet vertically and horizontally).

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Currently, there is no fire test standard for edge of roof detailing to evaluate vulnerability to ember accumulation in the gaps at the roof edge (for open eave and soffitted eave construction) and ember intrusion (via gaps in soffitted eave construction), direct flame impingement, or thermal transmission of heat from wildfires or proximate landscaping. The roof edge includes roof covering, underlayment, sheathing, fascia, and gutter and how these systems interact.
• As there are no fire tests for roof edges, it is unclear how weathering of materials prior to fire exposure or the impact of general wildfire environmental conditions (e.g., high winds, flying debris, impact from objects) will impact performance over time. However, many of the vulnerabilities related to weathering of a roof edge can be identified during inspection, e.g. warped edge materials that would make the area vulnerable to embers or flame, rusted drip edge, etc.

• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Roof - https://ucanr.edu/sites/fire/Prepare/Building/Roof/
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones, Technical Fact Sheet No. 5 - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf
  • Wildfire Resilient Detailing, Joint Systems, and Interfaces of Residential Building Components - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-detailing-joints.pdf
• National Fire Protection Association (NFPA)
  • Firewise Fact Sheets, Roofing Materials - https://www.nfpa.org/-/media/Files/Firewise/Fact-sheets/FirewiseFactSheetsRoofingMaterials.ashx

Combustible debris such as leaves and pine needles can accumulate in gutters, especially from nearby or overhanging trees. Due to difficulty in accessing upper stories of a home, gutters two and three floors high are even more problematic since they will be difficult to access and clean out on a regular basis. If ignited, combustible debris in the gutter will expose the edge of roof construction, typically the fascia and or roof sheathing. Depending on the condition of the wood and presence (or absence) of metal flashing at the edge of the roof, debris in the gutter may make it easier for fire to enter the interstitial roof space and potentially into the attic [40]. In addition, the material of the gutter is also a concern. Many gutters are constructed of plastic. Plastic gutters are typically made from polyvinyl chloride (PVC), which can melt and fall to the ground when exposed to flames or elevated radiant heat. While PVC will self-extinguish once the debris around and in it burns out (the chlorine acts as a fire retardant), the fact that the gutter may contain burning debris as it collapses creates another mechanism for fire spread along the façade of the building or to combustible fuel beds below.

• Gutters: A shallow trough fixed beneath the edge of a roof to catch and direct rainwater.

• Fascia or gutter boards: Horizontal roof trim located along the perimeter of the roof of a building, usually below the roof level, to cover the rafter tails at the eaves and to seal off the top of the siding along the rake [41].

• Gutter guard: Gutter guard is a generic term used to describe anything that goes over gutters to limit the accumulation of vegetative debris (e.g., leaves, needles, twigs) in the gutter. There are a range of gutter guards including brush inserts, foam inserts, DIY screen, micro-mesh, hood, etc. Gutter guards can be combustible or noncombustible.

Currently, there are no fire-rated gutter assemblies.

Currently, there is no fire test standard to evaluate the performance of gutter assemblies (e.g., gutter, gutter covers/devices, attachment details) to ember exposure, direct flame impingement or thermal transmission of heat from wildfires.

• 2024 International Wildland-Urban Interface (IWUI) Code: Section 505.4 Gutters and Downspouts
• 2024 International Building Code: Section 1502.3 Gutters
• 2022 California Building Code (CBC):
  • Section 1502.4 Gutters
  • Section 705A.4 Roof Gutters
• 2022 NFPA 1140 Standard for Wildland Fire Protection: Section 25.3.2 Roof Design and Materials

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Clean out debris from gutters, regularly, especially during fire season.
• Install metal flashing at the roof edge to provide additional protection to the roof edge [40]. Refer to Section 1.1.6 Roof Edge.
• Install corrosion-resistant, noncombustible gutters such as galvanized steel, copper, or aluminum [7] to replace plastic gutters.
• Install noncombustible gutter guards or covers to minimize the amount debris that may enter.
• Inspect gutter guards regularly to assure that they have not become dislodged.
• Replace or protect combustible construction proximate to the gutters and roof edge detailing (i.e., fascia, underlayment, roof framing, and battens) [15]. See Section 1.1.6 Roof Edge for additional mitigations.
• Where feasible/permitted, provide scuppers or interior roof drains instead of rainwater gutters [11].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Observations in real fire incidents suggest that metal drip edges aid in limiting ignition of the structure at the roof edge in a wildfire, particularly when vegetative debris catches fire in the gutter. Further testing is still needed.
• There are no fire test standards to evaluate the performance of gutter assemblies (i.e., gutters, fascia, roof edge details, gutter covers, and attachment details) when exposed to wildfire conditions.
• Little to no fire testing has been conducted to obtain the rate of fire spread from the gutter to the structure.
• Little to no fire testing has been conducted to find if plastic or vinyl gutters will propagate from embers if there is no combustible debris in the gutter. (Note: IBHS and NIST research on vinyl fencing indicates that ignition is difficult) [2].

• National Fire Protection Association (NFPA)
  • Firewise Construction 2012 - https://static.colostate.edu/client-files/csfs/pdfs/firewise-construction2012.pdf
• Fire Safe Marin
  • Gutters - https://firesafemarin.org/harden-your-home/fire-resistant-gutters/
• Ready For Wildfire
  • Gutters - https://www.readyforwildfire.org/cf-action/home-hardening-gutter/
• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Gutters - https://ucanr.edu/sites/fire/Preparedness/Building/Gutters/
• Federal Emergency Management Agency (FEMA)
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf

Roof eaves and associated soffits comprise the overhanging part of the lower edge of the roof that extends beyond the exterior walls of a building. These combined building features provide shading, water protection, and architectural style, but are also an area of the building that is highly susceptible to ignition from heat buildup in the under-eave area and ember intrusion through vents during a wildfire. Below is a list of the major concerns for eaves in a wildfire:

• Windborne embers, convective heat, and radiant heat can be trapped under roof eaves and associated upper portion of exterior walls, creating localized severe fire conditions [6]. These aspects of fire exposure can be further exacerbated where buildings have wider overhangs or are located on sloping terrain [22].

• Depending on how the under-eave area is constructed (e.g., “soffitted”, “open-eave”) and of what materials (e.g., combustible or noncombustible), the impact of direct flame, hot gases, radiation, ember accumulation, as well as ember intrusion at vent openings, gaps, and other joints will vary.
  • Where roof eaves, overhangs, and soffits are of combustible materials (as is oftentimes the case with residential buildings), the likelihood of ignition is increased, particularly with an open eave design [42].
  • Open-eaves typically have exposed roof framing, as well as more gaps/joints as part of the construction, presenting more opportunities for ember accumulation or intrusion through vents and flame and hot gas accumulation.
  • Metal soffit panels conduct heat and can distort, allowing the passage of embers and hot gases. Untreated wood soffit panels can ignite, and vinyl panels can melt or deform and fall away [42].
  • Soffits will often have inlet vents as part of the attic ventilation system. Unscreened soffits vents can allow embers and hot gases to enter the attic, potentially leading to ignition of the combustible materials in the attic [6]. Refer to Section 1.2.2 Soffit or Under-Eave Vents for more details.

• Once an eave, overhang, or soffit has ignited, fire can readily spread laterally, providing greater potential for fire spread into the attic [6].

• Fires in these areas are also often difficult to identify and extinguish [15].

• Boxed-in eave: Design where roof eave soffit is boxed-in with a horizontal underside or sloping rafter tails. The underside of the rafter tails are finished with an exterior covering.

• Fascia or gutter boards: Horizontal roof trim located along the perimeter of a building, usually below the roof level, to cover the rafter tails at the eaves and to seal off the top of the siding along the rake [41].

• Open eave: Design where exposed roof rafters extend beyond the exterior wall, creating an unenclosed space on the underside of the roof deck. Blocking is used to fill the space between the top of the exterior wall and the roof sheathing [43].

• Soffit: Encloses the underside of roof overhangs.

Fire test standards that detail tests to evaluate resistance of fire penetration and direct flame impingement of eaves, overhangs, and other projections, as well as tests to evaluate ember/flame resistance of vents, exist and are listed below. Soffits may be included in assemblies that receive fire resistance ratings, but the soffit itself does not.

• ASTM E2957 Standard Test Method for Resistance to Wildfire Penetration of Eaves, Soffits, and Other Projections: https://www.astm.org/e2957-17.html
• SFM Standard 12-7A-3 Materials and Construction Methods for Exterior Wildfire Exposure: Horizontal Projection Underside: https://www.hcd.ca.gov/building-standards/state-housing-law/wildland-urban-interface/docs/2010-part-2-cbc-ch7a.pdf
• ASTM E2886 Standard Test Method for Evaluating the Ability of Exterior Vents to Resist the Entry of Embers and Direct Flame Impingement: https://www.astm.org/e2886_e2886m-20.html

• 2024 International Wildland-Urban Interface (IWUI) Code:
  • Sections 504.3, 505.3 Protection of Eaves
  • Sections 504.10.1, 505.10.1 Vent Locations
• 2024 International Building Code (IBC): Section 705: Exterior Walls
• 2022 California Building Code (CBC):
  • 707A.5 Open Roof Eaves
  • 707A.6 Enclosed Roof Eaves and Roof Eave Soffits
• 2022 NFPA 1140 Standard for Wildland Fire Protection: 25.3 Roof Design and Materials

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Enclose open overhangs with soffits that have a minimum one-hour fire-resistance rating, ignition-resistant material, or fire-retardant materials rated for exterior use to minimize the chance of embers and hot gases contacting the joists, rafters or trusses, or the underside of the roof decking [42].
• Where possible, replace open eaves with soffited eaves.
• Use flat, horizontal soffits instead of attaching the soffits to the sloped joists, which creates sloped soffits. A flat soffit reduces the potential for entrapment of embers and hot gases [6]. However, either flat or slopped soffits are better than open eaves.
• Evaluate the fire-resistance of existing soffits and replace soffits that are not fire-resistant according to the guidance provided in FEMA Technical Fact Sheet No.8 located within The Home Builder's Guide to Construction in Wildfire Zones [6].
• In very high Fire Severity Zones, install exterior 5/8” fire-resistant gypsum board between the existing and new soffit materials for enhanced fire resistance [6].
• For fascia materials, use noncombustible or fire-resistant materials (e.g., fire-retardant-treated lumber, fiber-cement board, etc.) [6].
• If the fascia is combustible, cover the fascia board with a noncombustible or fire-resistant material like fire-retardant-treated lumber, fiber-cement board, etc [6]. Note that unless steps are taken to minimize chances of fire reaching the under-eave area, heat trapping and ignition with lateral flame spread will happen, with noncombustible fascia or not.
• Fill joints and gaps with fire rated caulking and other appropriate firestopping materials.
• Do not store firewood, construction materials, or other combustible materials under any overhang.
• Regularly inspect and clear accumulated debris from eaves and overhangs. Identify and repair any vulnerable areas.
• Avoid planting combustible vegetation under eaves and overhangs. That is, create and maintain a near-home noncombustible zone. This should be maintained regardless of the combustibility of the soffit materials used. Refer to Zone 0 in Part II of this Handbook.

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Fire testing does not account for weathering of materials prior to fire exposure or the impact of general wildfire environmental conditions (e.g., high winds, flying debris, impact from objects).
• “Ignition-resistant” eaves and soffits that have been tested against criteria from SFM Standard 12-7A-3 may be difficult to verify in-field. While a database of listed products based on this standard is maintained by the California Office of the State Fire Marshal, training is required to be able to identify these products in-field.
• Incorrect language is often used when referencing fire-resistance of soffits. The soffit itself does not receive a rating. It must be part of an approved assembly. Note that building codes do allow for compliance via ignition-resistant or noncombustible materials. However, these would not be considered to have a rating.

• National Fire Protection Association (NFPA)
  • Wildfire Research Fact Sheet-Under Eave Construction - https://www.nfpa.org/-/media/Files/Firewise/Fact-sheets/FirewiseFactSheetsUnderEaves.ashx
  • Reducing Wildfire Risks in the Home Ignition Zone - https://www.nfpa.org/-/media/Files/Training/certification/CWMS/ReducingWildfireRisksHIZ.ashx
• Colorado State Forest Service
  • FireWise Construction Site Design and Building Materials 2012 - https://static.colostate.edu/client-files/csfs/pdfs/firewise-construction2012.pdf
• Insurance Institute for Business & Home Safety (IBHS)
  • Wildfire Home Assessment and Checklist - https://www.iafc.org/docs/default-source/pdf/wildfire-checklist_ibhse1e8b15c78366c709642ff00005f0421.pdf?sfvrsn=5bdedd0d_0
• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Eaves - https://ucanr.edu/sites/fire/Preparedness/Building/eaves/
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones, Technical Fact Sheets No. 8 and No. 6 - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf

Windborne embers, convective heat, and radiant heat can be trapped under overhangs, eaves, and soffits due to unique fire induced flows during wildfire incidents. Eaves, overhangs, and soffits typically have vents as part of the attic ventilation system. If soffit vents are unprotected, embers and hot gases can readily enter the attic or other parts of the structure leading to ignition of interior building contents. Oftentimes, fires that initiate via embers into attics or other concealed spaces can go undetected for long periods of time.

• Soffit Vent: A continuous or intermittent vent installed along a soffit as part of the attic ventilation system of a building [6].

• Eaves: Eaves are located at the down-slope edge of a sloped roof and serve as the transition between the roof and fascia/wall [6].

• Overhangs: Overhangs are extensions of the roof beyond the exterior wall (i.e., the joists, rafters, or trusses, and the decking they support cantilever past the wall) [6].

The ember and direct flame impingement resistance of under eave area vents are defined by ASTM E2886 Standard Test Method for Evaluating the Ability of Exterior Vents to Resist the Entry of Embers and Direct Flame Impingement. This test standard prescribes two individual methods to evaluate the ability of the vent to resist: (1) the entry of embers and (2) flame intrusion. Full-scale tests at IBHS demonstrated that ASTM E2886-compliant vents limit the entry of large embers, and that the embers collected behind these vents (e.g., on the attic side) were small and incapable of igniting combustibles [22]. Note: ASTM E2886 does not provide explicit quantitative acceptance criteria for ember intrusion or flame intrusion. However, ember intrusion is evaluated based on observation of occurrence of combustion of a cotton pad on the unexposed side of the vent given a 3-min exposure to tumbled Class C brands. Performance criteria for the 10-min flame intrusion test as well as integrity test are specified in ASTM E2912. Visual observations are made for the presence and duration of any flame penetration through the vent. Acceptance criteria are typically not provided in ASTM standards, including this one [16]. Acceptance criteria are specified in the California Building Code (CBC) Section 706A.2, and NFPA 1140 Section 25.3.3.

• ASTM E2886/E2886M-14 Standard Test Method for Evaluating the Ability of Exterior Vents to Resist the Entry of Embers and Direct Flame Impingement: https://www.astm.org/e2886_e2886m-20.html
• ASTM E2912 Standard Test Method for Fire Test of Non-Mechanical Fire Dampers Used in Vented Construction: https://www.astm.org/e2912-17.html

• 2024 International Wildland-Urban Interface (IWUI) Code: Section 504.10, 505.10 Vents
• 2022 California Building Code (CBC): 706A Vents
• 2022 NFPA 1140 Standard for Wildland Fire Protection:
  • Section 25.7.4 Exterior Openings
  • 25.3.3 for Vents

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Cover existing vents with wire mesh screen having openings with a maximum of 1/8”, preferably 1/16”. Research has shown that 1/8” mesh screening can still lead to embers with sufficient energy to ignite fine fuels in the attics.
• Install ember resistant vents manufactured with wire mesh screening with a maximum of 1/8”, preferably 1/16”. Research has shown that 1/8” mesh screening can still lead to embers with sufficient energy to ignite fine fuels in the attics.
• Common 1/4” screens are ineffective and should be replaced.
• Replace screens that have been painted over or detached from the substrate.
• Do not use fiberglass or plastic mesh because they can melt and/or burn.
• Use fire-rated caulking around penetrations to seal openings.
• Protect vents in eaves or cornices with baffles to block embers, backed by 1/16” wire mesh (mesh alone is not enough) [24].
• If possible, move soffit vents away from the exterior wall.

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Fire testing does not account for weathering of materials prior to fire exposure or the impact of general wildfire environmental conditions (e.g., high winds, flying debris, impact from objects).
• ASTM E2886 does not evaluate the ability of vents to completely exclude entry of flames or embers, nor does it test for transmission of smoke or hot gases. This may be considered reasonable considering the functional use of the vent. That said, current test standards are likely inadequate in how a vent should be evaluated to both satisfy ventilation requirements and limit negative effects of fire, smoke and embers from leading to structure ignition.
• ASTM E2886 nor the building code provides acceptable performance criteria for ember intrusion, flame, or smoke resistance for vent openings.
• In most instances, it is challenging to verify, in-the-field, if an off-ridge vent has been fire-tested. (Professional judgement and discussion with the homeowner are required.) Training may be required to be able to identify fire-tested foundation vents and under-eave vents.
• Air flow calculations may need to be reconsidered or redesigned where fire rated vents are installed in existing structures, to ensure code required airflow is satisfied.

• Insurance Institute for Business & Home Safety (IBHS)
  • Ember Testing - https://ibhs.org/wildfire/building-vulnerability-to-ember-exposure/
  • Ember Testing - https://ibhs.org/wp-content/uploads/wpmembers/files/Vulnerability-of-Vents-to-Wind-Blown-Embers_IBHS.pdf
  • Ember Testing - https://www.facebook.com/watch/?v=389602881106017
  • Preparedness - https://disastersafety.org/wp-content/uploads/2021/08/WFR-Home-Preparedness-Guide.pdf
• National Fire Protection Association (NFPA) Firewise
  • https://www.nfpa.org/-/media/Files/Firewise/Fact-sheets/FirewiseFactSheetsAtticsCrawlSpaces.ashx
  • https://disastersafety.org/wp-content/uploads/2021/08/WFR-Home-Preparedness-Guide.pdf
• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Eaves - https://ucanr.edu/sites/fire/Preparedness/Building/eaves/
  • Wildfire Preparedness, Prepare Your Home, Vents - https://ucanr.edu/sites/fire/Prepare/Building/Vents/
• Federal Emergency Management Agency (FEMA)
  • Home Builders Guide to Construction in Wildfire Zones - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf

In general, joints and other penetrations create gaps in the continuity of a fire rated or fire resistive roof or wall assembly, providing a potential avenue for embers, hot gases, or flame to breach the exterior envelope of a building. Due to unique fire induced flows at the underside of eaves that can lead to an accumulation of hot gas and embers, head-of-wall to roof joints are particularly vulnerable to ember intrusion and exposure to hot gases. Embers can oftentimes accumulate at head-of-wall to roof joints, creating a concentrated source of heat. For bottom-of-wall to roof joints that may occur in more complex roofs (i.e., high number of vertical-to-horizontal transitions), the concern with hot gases accumulating near the joint are reduced. However, bottom-of-wall to roof joints are more susceptible to direct flaming and ember accumulation from the ignition of debris that typically collected in these locations. In addition, head/bottom-of-wall-to-roof joints are also locations where there can be different fire classification/rating levels and construction materials (which can result in one system being compromised by the other). Lastly, there is currently no fire test for any types of roof joints (including head-of-wall or bottom-of-wall joints to roof) to wildfire exposure - embers, direct flaming, or hot gases. Unprotected joints can undermine fire-resistant or ignition-resistant wall assembly.

• Joint: The opening in or between adjacent assemblies that is created due to building tolerances or is designed to allow independent movement of the building in any plane caused by thermal, seismic, wind or any other loading [35].

• Fire-Resistant Joint System: An assemblage of specific materials or products that are designed, tested and fire-resistance rated in accordance with a standard fire test to resist for a prescribed period of time the passage of fire through joints made in or between fire-resistance rated assemblies [35]. (Note: There are currently no fire-resistant joint system tests for wildfire exposures.)

• Head-of-Wall: A head-of-wall joint is the linear gap between the top of a wall assembly and bottom of a floor or roof assembly [44].

• Bottom-of-Wall: A bottom-of-wall joint is the linear gap between the bottom of a wall assembly and top of a roof or floor assembly.

• Flashing: A thin piece of metal that is installed at joints to protect against intrusion of unwanted elements such as water, and to protect combustible surfaces from ignition by embers that accumulate at wall intersections.

Currently, there is no fire test standard to evaluate ember intrusion, ember accumulation, direct flaming impingement, or thermal transmission of heat via convection or radiation from wildfires for joint systems (head-of-wall or bottom-of-wall-to roof joint system). Fire rated joints are necessary to maintain a roof or wall system's fire rating, integrity, and/or continuity to wildfire exposure. While a variety of fire tests exist for joint systems in interior building fire exposures (e.g., ASTM E1966 or UL 2079), none are applicable to the fire conditions presented by wildfires. A range of joint systems (e.g., static joints, movement joints) and joint conditions (e.g., header or top-of-wall, footer, or bottom-of-wall details) for exterior wildfire exposures are still needed.

Currently, there is no fire test standard to evaluate ember intrusion, direct flame impingement, or thermal transmission of heat via convection or radiation from wildfires for joint systems.

• 2024 International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC): No explicit requirements
• NFPA 1140 Standard for Wildland Fire Protection: No explicit requirements

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Debris should be removed from around all joints created at the roof (e.g., expansion joints, vents/chimney-to-roof joints).
• Corrosion-resistant metal flashing should be installed at bottom-of-wall-to-roof joints to limit ember accumulation and ignition or direct flame infiltrating the exterior wall or under-eave area in the case of a dormer or split-level design. Where the roof or wall underlayment is combustible, refer to appropriate protection measures in the roof and wall construction/covering section for detailing. The metal flashing should be lapped above the roof covering material, extending vertically up along the exterior side of the wall siding before being “let in” behind the siding at the lap joint, with combustible siding kept 4-6” above the roof surface [38].
• Use noncombustible construction where possible, in both new construction and retrofits [38].
• Provide fire-rated caulking in any gaps at the joint between the wall and the top of roof.
• In new construction, limit the complexity of roof design [38].

• Currently, there are no fire testing standards to evaluate ember intrusion, direct flame impingement, or thermal transmission of heat via convection or radiation from wildfires for joint systems.
• It is unclear how susceptible various head/bottom-of-wall-to-roof joints are to wildfire exposures.

• University of California, Agriculture and Natural Resources (UCANR)
  • Home Survival in Wildfire-Prone Areas: Building Materials and Design Considerations - https://anrcatalog.ucanr.edu/pdf/8393.pdf
• Federal Emergency Management Agency (FEMA)
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf
  • Wildfire Resilient Detailing, Joint Systems, and Interfaces of Residential Building Components - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-detailing-joints.pdf

Exterior wall assemblies for most residential buildings (i.e., single-family homes, duplexes, and 1-3 story townhomes) are typically not required to have any fire-resistance rating, unless separation distances are 5' or less to the property line. In addition, the exterior walls are also likely to be constructed using a combination of combustible and noncombustible cladding, and structural and insulation materials. Even in areas with adopted wildfire building codes, exterior walls will most likely only have ignition-resistant cladding such as stucco, fiber cement siding, masonry tiles, and not be a fire-resistance rated wall assembly. As such, the risk of structure ignition resulting from wildfire exposures, neighboring structures, or other proximate fuels in the landscape, particularly in a wind-driven events, are increased.

The main concerns with exterior wall assemblies are: (1) the large surface area and proximate location to a variety of fire sources (i.e., wildlands, adjacent structures, other proximate man-made fuels, and ornamental vegetation) increasing exposure to severe fire conditions (radiation, directing flame, hot gases, and embers) and (2) if the cladding and overall wall assembly is of combustible materials, not fire rated, not well maintained (i.e., gaps and unprotected joints), or is proximate to hazards, plants, trees and dead/dying debris, then it is far more vulnerable to ignition from wildfire. Additional concerns are described below:

• Exterior walls often have combustible structural elements (e.g., wood studs) and various combustible sublayers such as plywood sheathing, house wrap and insulation. If the integrity and continuity of the exterior cladding system is not well-maintained, small openings or gaps in the siding and trim can develop over time. This can provide an accumulation point for embers and entry point for hot gases or flames, both of which could result in fire penetrating the outer membrane of the cladding system, leading to ignition of combustible interior materials. A fire in combustible interstitial spaces can go unnoticed for long periods, allowing the fire to grow to uncontrollable levels before being detected.

• Any opening in exterior surfaces provides an entry point for ember intrusion including pet doors, HVAC plumbing, unsealed spigots, mail slots.

• Combustible items attached to exterior cladding will impact the integrity of the cladding, including plastic conduit for utility access to the structure, ornamental fixtures such as decorative shutters made of plastic or wood, combustible fences, or trellis elements.

• Wood shake or shingle cladding, due to its nature and method of construction, introduces numerous edges where embers can collect, potentially leading to structure ignition. In addition, combustible wall siding can lead to rapid fire spread along the surface of the entire wall, potentially reaching other vulnerable components, including windows, vents and the under-eave area.

All these concerns present challenges to limiting structure-to-structure spread, particularly for high-density housing. Several academic studies support these known vulnerabilities [22]. One such study, by Maranghides and Johnsson, reported that flames jetting out of a window ignited a mock wall assembly from 6 feet away in 80 seconds, in a test performed with no wind [45].

• Exterior cladding: The construction material applied over others in the exterior wall assembly [46].

• Fire-resistance rating: The time a building element, component, or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both, as determined by standard fire tests.

• Exterior wall assemblies: A system of wall components, including wall covering materials, that provides protection of the building structural members and occupants, including framing and sheathing materials, and conditioned interior space, from the detrimental effects of the exterior environment [47].

The fire resistance of external wall assemblies to interior and exterior fire exposures is defined by ASTM E119 or UL 263. This standard test method is applicable to assemblies of masonry units and to composite assemblies (e.g., concrete, steel) of structural materials for buildings, including loadbearing and other walls and partitions, columns, girders, beams, slabs, and composite slab and beam assemblies for floors and roofs [48].

This test standard is one of the most widely adopted methods for comparing the performance of building construction materials, elements, and assemblies to a standard fire exposure. It is used to measure and describe the response of a material or assembly to heat under controlled conditions (exposure via gas burners and is largely radiative with convective component). The test method includes measurements of exposed and unexposed surface temperature, as well as the ability of an element or assembly to maintain structural stability, integrity, and insulation when exposed to a severe, standard fire exposure. The standard fire exposure simulates severe interior building fire conditions during flashover conditions. Depending on how the wall assembly performs against the performance criteria for stability, integrity, and insulation, the assembly can achieve anywhere from a 30-min to 4-hour fire resistance rating.

Note: The test standard, however, does not by itself incorporate all factors required for fire hazard or fire risk assessment of the materials or assemblies under actual fire conditions. This is due to limitations of the size of the specimens tested, size of the furnace, standard fire exposure, etc [48].

• ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials: https://www.astm.org/e0119-20.html
• SFM Standard 12-7A-5 Materials and Construction Methods for Exterior Wildfire Exposure: Ignition-Resistant Material
• UL 263 Fire Tests of Building Construction and Materials: https://global.ihs.com/doc_detail.cfm?document_name=UL%20263&item_s_key=00097028
• ASTM E2707 Standard Test Method for Determining Fire Penetration of Exterior Wall Assemblies Using a Direct Flame Impingement Exposure: https://up.codes/viewer/california/ibc-2018/chapter/new_7A/sfm-materials-and-construction-methods-for-exterior-wildfire-exposure#new_705A
• ASTM E84 Standard Test Methods for Surface Burning Characteristics of Building Materials
• UL 723 Test for Surface Burning Characteristics of Building Materials
• NFPA 268 Standard Test Method for Determining Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source
• NFPA 285 Standard Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components

• 2024 International Wildland-Urban Interface (IWUI) Code: Section 504.5, 505.5 Exterior Walls
• 2024 International Building Code (IBC):
  • Section 705 Exterior Walls
  • Section 1402 Performance Requirements
  • Section 1405 Combustible Materials on the Exterior Side of Exterior Walls
• 2022 California Building Code (CBC): Section 707A.3 Exterior Wall Coverings
• 2022 NFPA 1140 Standard for Wildland Fire Protection:
  • Section 25.6 Exterior Vertical Walls
  • Section 25.7 Exterior Openings

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

Note: While noncombustible or ignition-resistant exterior wall coverings may provide an initial barrier to flames, heat can still pass through the coverings and ignite other components of the exterior wall assembly. For the most effective protection, ensure that the exterior wall assembly has been tested against criteria from ASTM E119 or UL 263 for a fire-resistance rating.

Note: As wildfire codes do not require or provide guidance on when and where fire-resistance rated wall assemblies should be provided and to what hourly rating, local fire experts or AHJs should use progressional judgement on hourly rating suggestions given the severity of the anticipated wildfire or proximate structure fire exposure.

• Maintain an ember-resistance zone for at least 5 feet from all exterior walls of the structure. Remove combustibles fuel loads including wood mulch, propane tanks, trash containers, plastic storage bins, BBQs, vegetation of all kinds (if possible, otherwise remove all high fire hazard vegetation).
• Maintain landscaping and general housekeeping within the home ignition zone. Refer to defensible space requirements.
• Consider upgrading the exterior wall cladding to include a 5/8” Type X exterior rated gypsum board between the wall cladding and underlayment or upgrade to a 1-hour fire rated wall assembly, where the building or home is within 30' of the property line or adjacent structure.
• Consider using fiberglass batt insulation or mineral wool inside exterior wall cavities to reduce potential for ignition of combustible concealed spaces. Ensure gaps in exterior walls, particularly cladding/bottom-of-wall to foundation detail, is flashed/sealed with fire resistant caulk completely [64].
• Refer to Section 1.4 Sprinkler Systems for mitigation strategies related to potential exterior sprinkler system applications.
• Protect any point which may allow ember penetration to structure.
• Regularly inspect exterior siding for gaps and holes. Where gaps or holes are present, use fire resistant caulk to seal the opening.

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Current building codes do not require fire resistance ratings for exterior walls for single family residences, duplexes, or 1-3 story townhomes regardless of fire separation distances to adjacent properties or structures. While fire separation distances exist in building codes, they are primarily designed for structure-to-structure spread from adjacent properties, they do not explicitly apply to outbuildings on the same property. The underlying basis for the separation distances and ratings are likely valid but need to be specified/confirmed for residential buildings.
• While the standard ASTM E119 fire resistance test is based on interior building fires or structure-to-structure fires, it was not specifically designed to account for the unique aspects of wildfire fire exposures. That is, it does not capture the impact of embers or direct flame impingement. That said, interior building fire exposures are generally more severe to exterior fire exposures, and therefore would provide a reasonable proxy for anticipating a rated-wall assembly's performance in a wildfire.
• ASTM E119 fire testing does not account for weathering of materials prior to fire exposure. UL 263 has an accelerated weather exposure protocol prior to fire testing.
• In most instances, it's challenging to verify in-the-field if an exterior wall assemblies fire resistance rating of 1-hour, 2-hour, etc. (Professional judgement required.)

• Insurance Institute for Business & Home Safety (IBHS)
  • Preparedness - https://disastersafety.org/wp-content/uploads/2021/08/WFR-Home-Preparedness-Guide.pdf
• National Fire Protection Association (NFPA)
  • Roofing Materials - https://www.nfpa.org/-/media/Files/Firewise/Fact-sheets/FirewiseFactSheetsRoofingMaterials.ashx
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
• FM-Global
  • Property Loss Prevention Data Sheet 9-19 - https://www.fm.com/resources/fm-data-sheets

Like other exterior openings, doors can compromise a home's ability to survive a wildfire when precautions are not taken to prevent them from being an entry point for embers and/or flames. During a wildfire, a door can be compromised due to an extended radiant heat exposure from surrounding vegetation or due to flames when embers have ignited vegetative debris near the door [49]. Deteriorating weather stripping and glass panes are the most vulnerable parts of the door. If the weather stripping has deteriorated around the door causing a poor seal, embers and flames can penetrate around the door into the structure. If the glass in a door breaks during a wildfire, embers and flame can easily enter a structure [50]. Similarly, non-fire rated combustible doors and combustible door frames can ignite or fail, leading to ember intrusion and ultimately ignition of other material inside of the structure. Therefore, doors must be able to resist the following exposures:

• A radiant exposure severe enough to break the glass in a door or ignite the door or door frame. Burning vegetation in close proximity to a door could also ignite non-fire rated combustible doors and combustible door frames [50].

• A flame contact exposure that could result from embers igniting vegetation and/or exterior cladding that burns up to the door(s) [50].

See Section 1.3.4 Windows for additional guidance on glass panels in doors.

• Weather Strip: A strip of material to cover the joint of a door or window and the sill, casing, frame, or threshold to exclude rain, snow, and cold air [51].

• Sidelite: The side panels on either side of the door. Filled with glass or wood and usually provided on both sides of a primary door, though can exist solo. Sidelites can be provided in the same overall frame as the door or may be independently framed.

Fire ratings for doors or door assemblies is defined by a number of standards, as follows:

• NFPA 252 Standard Method of Fire Tests of Door Assemblies
• UL 10B Standard Test for Fire Tests of Door Assemblies
• UL 10C Standard for Positive Pressure Fire Tests of Door Assemblies
• ASTM E152 Standard Methods of Fire Tests of Door Assemblies

These test standards prescribe specific fire and hose stream test procedures for fire door assemblies for determining the degree of fire protection provided by such assemblies in retarding the spread of fire (flame, heat, and hot gases) through door openings in a fire resistive wall when exposed to a severe, standard fire exposure [52]. The standard fire exposure simulates severe interior building fire conditions during flashover conditions. It does not represent the wildfire exposures that may also include embers and direct flame impingement. Depending on how the door assembly performs against the performance criteria defined in the standards, the door can achieve anywhere from a 20-min, 1-hour, or up to 3-hours (typically) fire resistance rating.

• ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials: https://www.astm.org/e2886_e2886m-20.html
• ASTM E152 Standard Methods of Fire Tests of Door Assemblies.
• ASTM E2112 Standard Practice for Installation of Exterior Windows, Doors, Skylights: https://www.astm.org/e2112-19c.html
• UL 10B Standard Test for Fire Tests of Door Assemblies: https://standardscatalog.ul.com/ProductDetail.aspx?UniqueKey=29319
• UL 10C Standard for Positive Pressure Fire Tests of Door Assemblies: https://www.shopulstandards.com/ProductDetail.aspx?UniqueKey=31216
• NFPA 252 Standard Methods of Fire Tests of Door Assemblies: https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=252

• 2024 International Wildland-Urban Interface (IWUI) Code: Chapter 5, Sections 504.9, 505.9 Exterior Doors
• 2022 California Building Code (CBC): Section 708A Exterior Windows, Skylights, and Doors
• 2022 NFPA 1140 Standard for Wildland Fire Protection: 25.7 Exterior Openings

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Provide, where possible, ignition-resistant or noncombustible framing materials (e.g., metal or metal-clad wood).
• Replace old hollow core doors with solid core or steel doors.
• Consider using tempered glass for sliding glass doors or glass panel inserts, which is stronger than annealed glass and will provide additional protection during a wildfire [53].
• Fabricate covers (for example, 1/2” plywood covers), cut to size and marked so that it can easily be installed over a door prior to evacuation. Shutters or other roll-down devices could also be installed [53].
• During a wildfire event, make sure all doors remain closed to avoid ember intrusion into structures.
• Manage vegetation and other types of items that could catch fire in the areas nearest to doors. This includes maintaining the surrounding vegetation and using noncombustible mulch and ignition-resistant materials for yard and garden structures near doors [54].
• The recommended glazing products for homes in wildfire zones are tempered glass, fiberglass-reinforced translucent glazing, and insulated glazing units (IGUs). Glazing products that are not recommended are annealed glass, ceramic glass, and plastic glazing [6].
• Consider installing a self-closing, metal screen door (with openings 1/8” or less) to protect against embers [15]. Note that typical screen doors have 1/16” mesh. However, this should be verified if possible.
• Exposed components (i.e., fixtures) should be made of noncombustible materials [15].
• Provide self-closing doors where possible [15].
• Ensure that any openings within the plane of the door (i.e., windows, dog doors) do not contain gaps and, where possible, are made of noncombustible materials [38].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Currently, there is no fire test standard to evaluate ember intrusion, direct flame impingement, or thermal transmission of heat via convection or radiation from wildfires for doors.
• Some gels and foams marketed for structure protection during wildfires indicate they will also protect doors, but verification of these claims by an independent source is not currently available [53].
• Glass breaking and/or fall-out is still within the realm of active fire testing and research for all the ranges of glazing types with associated frame types (e.g., wood, vinyl, aluminum, vinyl- and aluminum-clad wood, and fiberglass).
• Most evidence regarding external doors is anecdotal. More research in this area is needed [22].

• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Window - https://ucanr.edu/sites/fire/Prepare/Building/Windows/
• Fire Safe Marin
  • Fire Resistant Windows - https://firesafemarin.org/harden-your-home/fire-resistant-windows/
• Insurance Institute for Business & Home Safety (IBHS)
  • Creating a Fire Adapted Home - http://www.projectwildfire.org/wp-content/uploads/2016/02/IBHS-Guide-to-Creating-Fire-Adapted-Home.pdf
• Fire Safe San Mateo County
  • Windows - https://firesafesanmateo.org/preparedness/home-hardening/windows
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones, Technical Fact Sheet No. 10 - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf

Garage doors present vulnerabilities to the structure. These doors are not typically sealed very well due to lack of heating or cooling in these spaces. Gaps around garage doors provide entry point for embers into the garage structure. Homeowners often have large amounts of storage and other types of combustible fuels in garages, which may present higher risks if embers enter the garage space. Garages are not typically finished out with drywall, so the open studs provide exposed combustible material that is vulnerable to ignition. Some garage doors are also provided with small windows. These windows are vulnerable to direct flame impingement. For more information, see Section 1.3.4 Windows.

• Weather Strip: A strip of material to cover the joint of a door or window and the sill, casing, frame, or threshold to exclude rain, snow, and cold air [51].

• Sectional Garage Doors: Sectional garage doors are made up of panel sections that are connected with hinges. As the door opens and closes, wheels at the edge of each panel roll inside a vertical track on each side of the door opening [55].

Residential roll up garage doors are not fire rated.

• ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials: https://www.astm.org/e0119-20.html

• 2024 International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC): Section 708A.4 Garage Door Perimeter Gap
• 2022 NFPA 1140 Standard for Wildland Fire Protection: No explicit requirements

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Install ignition-resistant or noncombustible framing materials (e.g., metal or metal-clad wood).
• Ensure any weather stripping is in good condition and provides a tight seal.
• Use tempered glass, where glass panels are provided within a garage door. Tempered glass is 3-4 times more resistant to heat compared to annealed glass.
• Manage vegetation and other types of items that could catch fire in the areas nearest to garage doors. This includes maintaining the surrounding vegetation and using noncombustible mulch and ignition-resistant materials for yard and garden structures near garages [54].
• For pedestrian access doors into garages, refer to Section 1.3.2 Doors.
• Relocate any combustible or hazardous materials within the garage away from garage door or other openings, or within a protective cabinet to limit ignition, in the event embers enter the garage space.
• Ensure storage of goods and other hazardous materials are properly maintained and in appropriate containers, and that general housekeeping is maintained.
• If the garage door is not metal, install metal flashing at the bottom of the garage door for the first 6 inches from the ground [45].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Field and/or lab research is limited on the performance of garage doors during wildfire events.
• Fire testing of sealants around garage doors for radiant heat, direct flame impingement, and/or ember exposure is currently unavailable.
• Methods for providing fire protection for concrete surface below the garage door where the concrete has settled.

• University of California, Agriculture and Natural Resources (UCANR)
  • Garages - https://ucanr.edu/sites/fire/Preparedness/Building/Garage/
• Fire Safe Marin
  • Chimneys, Garages, Driveways, & Address Numbers - https://firesafemarin.org/harden-your-home/chimneys-garages-driveways-address-number/
• Insurance Institute for Business & Home Safety (IBHS)
  • Creating a Fire Adapted Home - http://www.projectwildfire.org/wp-content/uploads/2016/02/IBHS-Guide-to-Creating-Fire-Adapted-Home.pdf
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones, Technical Fact Sheet No. 10 - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf

Windows can compromise a home's ability to survive a wildfire when precautions are not taken to prevent them from being an entry point for embers and/or flames. During a wildfire, a window can be compromised due to an extended radiant heat exposure from surrounding vegetation or to flames when embers have ignited vegetation near the window. The glass is the most vulnerable part of the window. If the glass in a window breaks during a wildfire, embers and flame can easily enter a structure. Similarly, combustible window frames can ignite or fail, leading to ember intrusion and ultimately ignition of other material inside of the structure. Therefore, windows must be able to resist the following exposures [53]:

• A radiant exposure severe enough to break the glass in a window or ignite the window frame or the exterior siding directly below it. Burning vegetation in close proximity to a window could also ignite combustible siding [53].

• A flame contact exposure could result from embers igniting vegetation and/or exterior cladding that burns up to the window(s) [53].

• Glass breakage occurs because of thermally induced strains caused by temperature differences between the shielded glass protected by the frame and the exposed glass away from the frame. This non-uniform heating causes the glass to expand at different rates [53]. The presence of a rigid frame also restrains the glass from expanding, leading to cracking of the glass. If the temperature differences are large enough, the cracks grow, potentially leading to failure of glass and fall out.

• Double (dual)-Pane Window: Window provided with two panes of glass to slow the heat transfer across the window. This also provides a security factor should one pane break during a fire event. Dual-pane windows initially became common in construction as a result of more restrictive energy codes as dual-pane windows are more energy efficient. An added benefit is that dual-pane windows are less vulnerable to breakage when exposed to heat.

Windows can comply with several different requirements to resist the effects of fire. Applicable options are as follows:

• Be constructed of multi-pane glazing with a tempered pane [31].
• Be constructed of glass block units [31].
• Have a fire-resistance rating of not less than 20 minutes when tested in accordance with NFPA 257.
• Have a fire-resistance rated glazing with performance tested in accordance with ASTM E119.

• ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials: https://www.astm.org/e0119-20.html
• ASTM E 2112 Standard Practice for Installation of Exterior Windows, Doors, Skylights: https://www.astm.org/e2112-19c.html
• UL 263 Fire Tests of Building Construction Materials: https://global.ihs.com/doc_detail.cfm?document_name=UL%20263&item_s_key=00097028
• NFPA 257 Standard on Fire Test for Window and Glass Block Assemblies: https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=257
• SFM Standard 12-7A-2 Exterior Windows

• 2021 International Wildland-Urban Interface Code (IWUIC): Sections 504.8, 505.8 Exterior Glazing
• 2022 California Building Code (CBC):
  • Chapter 24 Glass and Glazing
  • Section 708A Exterior Windows, Skylights, and Doors
• 2022 NFPA 1140 Standard for Wildland Fire Protection:: Section 25.7 Exterior Openings
• 2017 NFPA 257 Standard on Fire Test for Window and Glass Block Assemblies
• 2017 NFPA 252 Standard Method of Fire Tests of Door Assemblies
• 2019 NFPA 80 Standard for Fire Doors and Other Opening Protectives

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Install ignition-resistant or noncombustible framing materials (e.g., metal or metal-clad wood).
• Replace old single-pane windows with dual-pane windows.
• Close all windows during a wildfire or before evacuating.
• Consider using tempered glass, which is stronger than annealed glass and will provide additional protection during a wildfire [53].
• Consider using insect screens. Screens fabricated from corrosion-resistant, noncombustible materials are preferred. Plastic clad fiberglass screens will fail as a result of a flame contact exposure.
• Fabricate covers (for example, 1/2” plywood covers), cut to size and marked so that it can easily be installed over a window prior to evacuation. Shutters or other roll-down devices could also be installed [53].
• Install noncombustible window screens of at least 1/16”.
• Manage vegetation and other types of items that could catch fire in the areas nearest to windows. This includes maintaining the surrounding vegetation and using noncombustible mulch and ignition-resistant materials for yard and garden structures near windows [32].
• Exterior shutters can provide protection in a wildfire. Solid metal shutters are recommended over wooden or plastic shutters. A wood covering (e.g., plywood) will protect the window from embers and radiant heat until the covering fails. If the building is located in a windborne debris region within a hurricane-prone region, the shutter should meet the windborne debris criteria in ASCE 7-05. Note that temporary shutters are only effective if the homeowner has sufficient time to put the shutters into place [6].
• The recommended glazing products for homes in wildfire zones are laminated glass, tempered glass, and insulated glazing units (IGUs). See Table 24 for more information. Glazing products that are not recommended are single pane annealed glass and plastic glazing [6].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Glass breaking and/or fall-out is still within the realm of active fire testing and research for all the ranges of glazing types with associated frame types (e.g., wood, vinyl, aluminum, vinyl- and aluminum-clad wood, and fiberglass).
• Theoretically it would be possible to polish the edges of the glass for windows, thereby minimizing the number of edge flaws present, making the glass less vulnerable to breakage. Whether this could be a long-term solution in terms of maintaining the polished edge during the processing in making the window has not been determined [50].

• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Preparedness, Prepare Your Home, Window - https://ucanr.edu/sites/fire/Prepare/Building/Windows/
• Fire Safe Marin
  • Fire Resistant Windows - https://firesafemarin.org/harden-your-home/fire-resistant-windows/
• Insurance Institute for Business & Home Safety (IBHS)
  • Creating a Fire Adapted Home - http://www.projectwildfire.org/wp-content/uploads/2016/02/IBHS-Guide-to-Creating-Fire-Adapted-Home.pdf
• Fire Safe San Mateo County
  • Windows - https://firesafesanmateo.org/preparedness/home-hardening/windows
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones, Technical Fact Sheet No. 10 - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf

In general, joints create gaps in the continuity of a fire rated or ignition-resistant wall assembly, presenting a potential pathway for hot gases, flames, or embers to penetrate the wall assembly and into the building interior or the outer membrane of the cladding system, leading to ignition of combustible interstitial spaces. A fire in combustible interstitial spaces can go unnoticed for long periods, allowing the fire to grow to uncontrollable levels before being detected. Joints can also create places for the accumulation of combustible debris that can be easily ignited by embers, hot gases, or direct flaming. Embers can accumulate at windowsills, door framing and at wall-to-wall intersections (such as an interior corner), creating a concentrated source of heat that may compromise the integrity of the wall, window, or door. In addition, there is currently no fire test for joints in wall assemblies to wildfire exposures - embers, direct flaming, or hot gases. This can create a short-circuit of a fire resistance rated (e.g., 1-hour, 2-hour), ignition-resistant, or fire resistive exterior wall.

• Joint: The opening in or between adjacent assemblies that is created due to building tolerances or is designed to allow independent movement of the building in any plane caused by thermal, seismic, wind or any other loading [9].

• Fire-Resistant Joint System: An assemblage of specific materials or products that are designed, tested and fire-resistance rated in accordance with a standard fire test to resist for a prescribed period of time the passage of fire through joints made in or between fire-resistance rated assemblies [9]. (Note: There are currently no fire-resistant joint system tests for wildfire exposures.)

• Flashing: A section of thin sheet metal that is installed at joints to protect against intrusion of unwanted elements such as water and embers. In the wildfire context, the flashing is primarily to protect an underlying combustible material. In the case of a drip edge, there would be a second function of minimizing ember accumulation or entry in gap between sheathing and fascia.

• Expansion Joint: A physical discontinuity that spans the entire breadth of an element in a building, creating two separate sections of the element instead of one bigger one. They are designed and configured to allow the different sections or elements to move independently of each other, so the elements don't become overstressed, crack or break [37] under various loads (e.g., thermal expansion/contraction, seismic movement).

Currently, there is no fire test standard to evaluate ember intrusion, direct flame impingement, or thermal transmission of heat via convection or radiation from wildfires for joints in wall assemblies. Fire rated joints are necessary to maintain a wall assembly's fire rating, integrity, and continuity to wildfire exposure. While a variety of fire tests exist for joints in interior building fire exposures (e.g., ASTM E1966 or UL 2079), none are explicitly designed for the fire conditions presented by wildfires. A range of joint systems (e.g., static joints, movement joints) and joint conditions (e.g., window-to-wall, door-to-wall, wall-to-wall, expansion joints) for exterior wildfire exposures are still needed.

Currently, there is no fire test standard to evaluate ember intrusion, direct flame impingement, or thermal transmission of heat via convection or radiation from wildfires for joint systems (wall joints or otherwise). Note: While there are no specific fire tests for exterior joints to wildfire exposure, many of the existing test methods (e.g., ASTM E119, ASTM E84) can be used to evaluate the impact of joints on performance.

• 2024 International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC): No explicit requirements
• 2022 NFPA 1140 Standard for Wildland Fire Protection: No explicit requirements

Additional local requirements, policies and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• IRC (if applicable - check for wildfire amendments).

• All combustible materials should be cleared away from doors both on the interior and exterior sides.
• Ensure there is no vegetation or other combustible materials within 5' of windows and glass doors.
• Clear debris from windowsills, wall-to-wall joints, and other surfaces where combustible debris collects near wall joints.
• Seal any gaps at wall joints with firestopping (i.e. mineral wool, fire caulking, and fire-rated sealants [38]) and through-penetration systems as needed to maintain the continuity of the exterior wall assembly.
• Repair damage to foundation wall and cladding to reduce the accumulation of embers and fire brands between damaged materials.
• Where possible, use or replace existing expansion joints with noncombustible materials [38].
• Install a minimum 6” noncombustible vertical separation where horizontal surfaces meet the wall [20].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Currently, there is no fire test standard to evaluate ember intrusion, direct flame impingement, or thermal transmission of heat via convection or radiation from wildfires for joint systems.
• No set of catalogs of “listed” fire resistive joint systems, products, and fire-rated assemblies at the national level exists for exterior building components and associated joints, detailing or interfaces exposed to wildfires in combination with weathering pre-tests. (California has state-approved WUI products, but there are limited joint and other interface detailing products specific to WUI [38].)
• It is unclear how susceptible various wall joints or functional gaps around doors are to wildfire exposures.

• Insurance Institute for Business & Home Safety (IBHS)
  • Preparedness - https://disastersafety.org/wp-content/uploads/2021/08/WFR-Home-Preparedness-Guide.pdf
• National Fire Protection Association (NFPA)
  • Roofing Materials - https://www.nfpa.org/-/media/Files/Firewise/Fact-sheets/FirewiseFactSheetsRoofingMaterials.ashx
• Federal Emergency Management Agency (FEMA)
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf
  • Wildfire Resilient Detailing, Joint Systems, and Interfaces of Residential Building Components - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-detailing-joints.pdf
  • Home Builder's Guide to Construction in Wildfire Zones - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf

Architectural embellishments are decorative in nature and not part of the engineered structure. In this sense these attachments do not add to the structure stability but can significantly compromise the structure by providing locations for ember accumulation or transfer of heat through connecting methods to the structure itself. In some cases, the architectural features can present a fuel load itself, if comprised of combustible, unprotected materials. Some balconies on buildings are solely architectural embellishments, where they are purely for aesthetics and not load-bearing. (Note: Refer to Section 1.3.7 Balconies, Decks, and Porches Construction & Surfaces for additional information where decorative balconies are provided.)

• Architectural Embellishment: A decorative detail or feature added to the exterior of the building to enhance the aesthetics.

• Ornament: An applied embellishment in various styles that is a distinguishing characteristic of buildings. Ornamentation often occurs on entablatures, columns, and the tops of buildings and around entryways and windows, especially in the form of moldings [60].

There are currently no fire classifications or ratings for architectural embellishments and ornaments.

Currently, there is no fire test standard to evaluate the performance of architectural embellishments during wildfires. There are also no fire tests to assess the contribution of these architectural features to the vulnerability of buildings in wildfire incidents (e.g., if they significantly contribute to building ignition, heat transfer to interior spaces, lead to ignition of exterior walls).

• 2024 International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC): Section 710A Accessory structures
• 2022 NFPA 1140 Standard for Wildland Fire Protection: Section 25.4 Overhanging Projections

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Remove combustibles (e.g., furniture, firewood, BBQs, mulch, vegetation, ornamental landscaping) from areas under decorative overhangs that could create a localized fire that ignites these decorative features.
• Seal any openings that may allow passage of embers or flame into a structure with firestopping and fire caulking.
• Upgrade attachment points of artwork and other decorative panels such that they fixed further away from the exterior wall where embers could collect.
• Consider replacing combustible architectural embellishments with noncombustible materials.

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• There is no fire test standard to evaluate the performance of architectural embellishments during wildfires.
• There are no fire tests to assess the contribution of these architectural features to the vulnerability of buildings in wildfire incidents (e.g., if they significantly contribute to building ignition, heat transfer to interior spaces, lead to ignition of exterior walls).
• There are limited codes and standards on the resiliency of these elements to wildfires.

• Federal Emergency Management Agency (FEMA)
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf

Balconies and decks can pose a significant hazard in the event of a wildfire. One of the main concerns associated with balconies and decks is the large surface area they present for collecting embers, leading to ignition of materials located on the balcony/deck or the balcony/deck itself. Similar to eave overhangs, unique fire induced flows can lead to the accumulation of embers and hot gases in the underside of balconies or elevated decks, potentially leading to ignition of the balcony/deck, particularly where the framing elements are exposed and of combustible construction. In a 2022 study, Hedayati et al. found that once combustible deck joists are ignited during a wildfire, the joists can burn for extended periods of time, exposing the bottom side of the deck boards to flames, ultimately leading to ignition of the entire deck [22]. In addition, most homeowners tend to store various types of combustible fuel loads below and on balconies/decks, such as combustible furniture, BBQs, wood piles etc. Balconies/decks can also introduce additional interfaces with the main structure, presenting numerous joints and potential gaps in the continuity of the exterior wall envelope, which may or may not be fire rated.

For combustible decks and other similar features (e.g., combustible stairs) that are at or near grade, these building components are also susceptible to direct flame impingement from surface fuels and other proximate vegetation. Many existing commercial or residential decks are constructed with less expensive combustible materials such as untreated wood, plastics, and wood-plastic composite products, which are vulnerable to ember and heat exposure in a wildfire event. Higher density deck boards (ipe-like hardwoods and plastic composites) are far less vulnerable to ember ignition than lower density decking (redwood and western red cedar). In addition, decks can oftentimes be built on a slope with hazardous vegetation below, where, if ignited, would result in increased exposure severity to the deck [6]. To limit storage of combustible goods, vegetative debris collection, and other fuel loads from accumulating below a combustible deck, a noncombustible enclosure or skirt around the underside of the deck should be provided. Note, the under-deck enclosure should also be designed to accommodate any flood mitigation measures particularly for decks on slopes greater than 10% (e.g., stop under-deck enclosure 6” from the ground) [25]. In addition, to vertical enclosure around the underside of deck structures, a fire-resistance rated horizontal surface may be needed, but only in the cases where combustible decks have solid walking surfaces. Material selection, orientation, design, storage, and landscaping practices around the deck are all critical to reducing the risk of ignition of the deck and the home.

• Balcony: A platform enclosed by a wall or balustrade on the outside of a building, with access from an upper-floor window or door [61].

• Deck: A flat surface capable of supporting weight, similar to a floor, but typically constructed outdoors, often elevated from the ground, and usually connected to a building [62].

• Flashing: A sheet of thin, impervious material used to prevent water penetration or seepage into a building and to direct the flow of moisture in walls [63].

Balconies, decks, and other similar projections of combustible construction are treated similar to floors in building codes and therefore are required to be fire-resistance rated, if the code requires floors in the building to achieve a fire resistance rating (e.g., per Table 601 of the International Building Code.) That said, building codes oftentimes allow exceptions for balconies and decks (e.g., balconies/decks in Types III, IV, and V construction are permitted to be of any material where sprinkler protection is extended to these areas). This means, balconies and decks in most residential homes are not required to be fire rated.

The IWUI Code provides a range of options for appendages and projections such as decks and balconies, including 1-hour fire resistance rating per ASTM E119.

The State of California has its own set of State Fire Marshal Standards (SFM) which also tests decking materials, and has been adapted into ASTM E2632 with some modification. Decking materials need to meet the performance requirements of these standards. Chapter 7A of the California Building Code provides a complete list of assembly options for the walking surface material of decks, porches, balconies, and stairs in relation to the fire test standards listed below.

• ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials: https://www.doi.org/10.1520/E0119-22
• ASTM D2898 Standard Practice for Accelerated Weathering of Fire-Retardant-Treated Wood for Fire Testing: https://www.astm.org/d2898-10r17.html
• ASTM D7032 Standard Specification for Establishing Performance Rating for Wood-Plastic Composite and Plastic Lumber Deck Boards, Stair Treads, Guards, and Handrails: https://www.astm.org/d7032-21.html
• ASTM D6662 Standard Specification for Polyolefin-Based Plastic Lumber Decking Boards: https://www.astm.org/d6662-17.html
• ASTM E84 Standard Test Method for Surface Burning Characteristics of Building Materials: https://www.astm.org/e0084-21a.html
• ASTM E2726 Standard Test Method for Evaluating the Fire Test Response of Deck Structures to Burning Brands
• ASTM E2632 Standard Test Method for Evaluating the Under-Deck Fire Test Response of Deck Materials
• ASTM E2768 Standard Test Method for Extended Duration Surface Burning Characteristics of Building Materials: https://www.astm.org/e2768-11r18.html
• UL 723 Standard for Test for Surface Burning Characteristics of Building Materials: https://standardscatalog.ul.com/ProductDetail.aspx?productId=UL723
• SFM Standard 12-7A-4, Decking: A two-part test consisting of a heat release rate (Part A) deck assembly combustion test with an under-deck exposure of 80 kW intensity direct flame for a 3-minute duration, and a (Part B) sustained deck assembly combustion test consisting of a deck upper surface burning ember exposure with a 12 mph wind for 40 minutes.
• SFM Standard 12-7A-4A Decking Alternate Method A: A heat release rate deck assembly combustion test with an under-deck exposure of 80 kW intensity direct flame for a 3-minute duration.
• SFM Standard 12-7A-5 Ignition-resistant Material: A generic building material surface burning flame spread test standard consisting of an extended 30-minute ASTM E84 or UL 723 test method as issued for fire-retardant-treated wood.

• 2024 International Wildland-Urban Interface (IWUI) Code:
  • 504.6, 505.6, 506.3 Underfloor Enclosure
  • 504.7 & 505.7 Appendages and Projections
• 2022 California Building Code (CBC):
  • Section 707A.7 Exterior Porch Ceilings
  • 707A.8 Floor Projections
  • 707A.9 Underfloor Protection
  • 707A.10 Underside of Appendages
  • 709A Decking
• 2022 NFPA 1140 Standard for Wildland Fire Protection:
  • Section 25.4 Overhanging Projections
  • A structural assessment rating form and guide included in Appendix A material associated with Chapter 24 provides an assessment of siding and deck building construction material.

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• For balconies and decks of combustible construction, consider providing the following:
  • Enclosing the underside of the balcony or deck with a noncombustible, vertical enclosure around the outer perimeter of the balcony/deck from the underside of the deck or balcony to grade.
    • If the deck or balcony is over a 10% slope or greater, the enclosure should stop within 6 inches above the ground surface to allow for drainage [64].
    • Where a solid, fire-resistant or ignition-resistant enclosure is provided, ensure appropriate venting is provided and appropriately protected to limit ember intrusion.
  • Replacing any combustible structural supports with noncombustible or ignition-resistant construction materials. Note: Heavy timber supporting elements do not need to be replaced or require protection [14].
  • Where the walking surface is solid, provide one layer of 5/8” Type X gypsum sheathing applied behind the exterior covering on the underside of the balcony or deck.
  • Where possible, access to the underside of the balcony and/or deck should be provided so that regular cleaning of debris can be undertaken prior to core fire season [7].
  • Create a noncombustible zone under the deck or balcony, including a 5' zone around the perimeter. Lay weed barrier and a top level of gravel under and around the deck to minimize the opportunity for vegetation to grow under or near the deck or balcony.

• Replace combustible furniture and cushions/coverings with noncombustible materials, where kept on or under balconies or decks.

• At the connection point of decks and balconies to the main structure, consider:
  • Install metal flashing on ledger boards without any gaps to limit embers and prevent water from accumulating and igniting the main structure or home.
  • Seal any gaps and joints with appropriate firestopping and fire caulking to prevent ember or flame intrusion [6]. The flashing should extend at least 18” (6” for retrofits) up the wall and be tucked in behind the lap joint [65].
  • Alternatively, if the exterior building siding is combustible, remove the bottom two to three courses of siding and replace them with noncombustible siding [65].

• Repair damage to deck or balcony walking surface.

• Keep the deck clear of debris, vegetation, and combustible materials (e.g., seat cushions, straw mats, rugs, pine needles, firewood, etc.). Remove needles and leaf litter from deck board gaps and the deck-to-house connection where embers may easily accumulate.

• Retrofitting the deck is also an option:
  • If the existing deck frame is structurally sufficient, remove the existing deck boards and install new ignition-resistant decking such as those comprised of aluminum, steel, autoclaved aerated concrete, noncombustible tile, or fire-retardant treated wood.
  • Do not use plastic composite deck boards unless the manufacturer has provided documentation that they are noncombustible. Plastic composite and non-FRT wood deck boards are combustible and should not be used.
  • For new construction, apply foil-faced self-adhering bitumen along the length and tops of the joists supporting the deck, and position the tape on each side of the joist near the top where the deck boards are attached [65].
  • If fully replacing a combustible deck surface is not feasible, ensure that under-deck exposure hazards have been addressed (remove combustibles under the deck), and replace the boards closest that are parallel and within one foot of the adjacent exterior wall of the house with a noncombustible material of the same thickness as the rest of the deck [65].
  • Replace dimensional timber railings with railings constructed of fire-resistant materials such as metal, tempered glass, cables, or 4-inch nominal thickness fire-retardant-treated wood [6].
  • When the deck, balcony, stairs, or ramp can accommodate or be reinforced to accommodate additional load, install brick or concrete pavers and a suitable drainage mat over the existing decking [6].

• Install metal flashing on ledger boards that are attached without gaps (Figure 1.65) [38].

• Where possible, replace any stairs and associated handrails that are connected to decks with noncombustible materials. Where this is not achievable, the following actions are recommended [66]:
  • Where stairs are 4 feet or less in width and open underneath, replace the first 6 vertical inches of the bottom of the stairs with noncombustible material. Stair treads should be replaced with noncombustible, solid material.
  • Where stairs are over 4 feet in width and open underneath, clear the underneath of the stair and enclose with solid fire-resistant materials or 1/16” non-corrosive metal screening. Replace the first 6 vertical inches of the bottom of the stairs with noncombustible material. Stair treads should be replaced with noncombustible, solid material. Where the bottom of the stair is enclosed, ensure that it is properly ventilated and provide appropriate vent protection for embers.

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Wildfire building codes and standards do not provide a clear definition or distinction for balconies and decks. It is unclear which provisions are applicable.
• There is no prioritized list of retrofit ideas which include the most effective methods to improve the fire resistance of existing decking.

• Insurance Institute for Business & Home Safety (IBHS)
  • Preparedness - https://disastersafety.org/wp-content/uploads/2021/08/WFR-Home-Preparedness-Guide.pdf
  • Wildfire Retrofit Guide - https://disastersafety.org/wp-content/uploads/2019/03/Wildfire-Retrofit-Guide-California_IBHS.pdf
• National Fire Protection Association (NFPA)
  • Firewise Toolkit - https://www.nfpa.org/-/media/Files/Firewise/Toolkit/FirewiseToolkit.ashx?la=en
• National Fire Protection Association (NFPA) Firewise
  • Safer from the Start - https://www.nfpa.org/-/media/Files/Training/certification/CWMS/SaferFromtheStart.ashx
• University of California, Agriculture and Natural Resources (UCANR)
  • Wildfire Home Retrofit Guide - http://www.readyforwildfire.org/wp-content/uploads/Wildfire_Home_Retrfit_Guide-1.26.21.pdf
  • Deck - https://ucanr.edu/sites/fire/Prepare/Building/Deck/
• Fine Home Building - https://www.finehomebuilding.com/membership/pdf/9390/021s41055.pdf
• Federal Emergency Management Agency (FEMA)
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf
  • Home Builder's Guide to Construction in Wildfire Zones - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf

The intrusion of embers through crawl space or basement vents is a vulnerability that can lead to structure ignition during wildfires. The main concern with crawl space/basement vents is that they can provide several openings where windborne embers, convective heat, and flames from wildfires (particularly surface fuels) can enter the structure and potentially cause ignition of interior building contents and other building components. Both vent inlets and outlets are sources of vulnerability. Debris can also accumulate at crawl space/basement vent openings, providing a source of combustible fuels for ignition.

• Crawl Space: An unoccupied, unfinished, narrow space within a building, between the ground and the first (or ground) floor. The area is called a crawl space because there is typically only enough room to crawl rather than stand (about 3' to 5') [67].

• Crawl Space Vents: Active or passive openings or vents through foundation walls or exterior walls providing aeration of the under-floor space between the bottom of the floor joists and the earth under a building (except space occupied by a basement) [68].

• Ember: Small burning or glowing pieces of vegetation or other cellulosic-based material.

• Vent: A device or assembly placed in an exterior opening of a building that allows for aeration.

The ember and direct flame impingement resistance of vents mounted on vertical walls is defined by ASTM E2886 Standard Test Method for Evaluating the Ability of Exterior Vents to Resist the Entry of Embers and Direct Flame Impingement. This test standard prescribes two individual methods to evaluate the ability of the vent opening to resist embers and flame. The ability of such vents to completely exclude entry of flames or embers is not evaluated. Acceptance criteria are not provided in this standard [16]. However, performance criteria are specified in the California Building Code (CBC) Section 706A.2 and NFPA 1144 Section 5.3.3.

• ASTM E2886/E2886M-14 Standard Test Method for Evaluating the ability of Exterior Vents to Resist the Entry of Embers and Direct Flame Impingement: https://www.astm.org/e2886_e2886m-20.html
• ASTM E2912 Standard Test Method for Fire Test of Non-Mechanical Fire Dampers Used in Vented Construction: https://www.astm.org/e2912-17.html

• 2024 International Wildland-Urban Interface (IWUI) Code: 504.10, 505.10 Vents
• 2022 California Building Code (CBC): 706A Vents
• 2022 NFPA 1140 Standard for Wildland Fire Protection: 25.3.3 Vent Assemblies

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Common 1/4” screens are ineffective and should be replaced.
• Install vents that are listed to ASTM E2886 or those listed by the California Office of the State Fire Marshal's Building Materials Listing Program [70].
• Cover existing vents with wire mesh screen having openings with a maximum of 1/8”, preferably 1/16”. Research has shown that 1/8” mesh screening can still lead to embers with sufficient energy to ignite fine fuels in the attics.
• Replace screens that have painted over or detached from the substrate.
• Vent and covering materials used shall be noncombustible, and corrosion resistant. Do not use fiberglass or plastic mesh because they will melt when exposed to flames [24].
• Use fire-rated caulking around penetrations to seal openings.
• Inspect and maintain vegetation in the vicinity of crawl space vents [71]. Remove combustible fuel loads including vegetation within 0-5' of building perimeter [24], [49].
• Clean vents on a regular basis to minimize buildup of debris in the mesh [24].
• Consider making vent covers that can be installed prior to the approach of a wildfire (and removed after the wildfire has passed) [24].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Fire testing does not account for weathering of materials prior to fire exposure or the impact of general wildfire environmental conditions (e.g., high winds, flying debris, impact from objects).
• ASTM E2886 does not evaluate the ability of vents to completely exclude entry of flames or embers [16].
• In most instances, it's challenging to verify in-the-field if a vent has been fire-tested. (Professional judgement and discussion with the homeowner are required.)
• Air flow calculations may need to be reconsidered or redesign where fire rated vents are installed in existing structures, to ensure sufficient airflow is still satisfied for non-fire purposes.

• National Fire Protection Association (NFPA)
  • Wildfire Research Fact Sheet - https://www.nfpa.org/-/media/Files/Firewise/Fact-sheets/FirewiseFactSheetsAtticsCrawlSpaces.ashx
  • Firewise How to Prepare Your Home for Wildfire - https://www.nfpa.org//-/media/Files/Firewise/Fact-sheets/FirewiseHowToPrepareYourHomeForWildfires.pdf
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf

Window/light wells, while serving several uses to the home, present multiple wildfire vulnerabilities. The design of the well creates deep corners along the exterior wall which encourages dry leaves, pine needles, and other combustible litter or debris to gather. Debris ignition can present a source of flame exposure to the structure, particularly at the window opening it surrounds. The configuration of these wells creates a hazardous condition where combustible materials that have collected in the light/window well over time will be directly adjacent to the window and frame, which already experience their own vulnerabilities.

• Window/lightwell: U-shaped, ribbed metal or plastic product designed to fit around basement windows, providing a space between the window and the surrounding earth to allow light into sub-grade structures. More notably, a window well can prevent water damage to a basement while also providing a route for an emergency escape and rescue opening with a finished sill height below the adjacent ground level during an emergency [68], [72].

• Window/lightwell covers: A physical barrier between the well and the ground elements to prevent debris build-up in the well. The covering can be constructed of mesh, plastic bubble covers, grill-type, etc. Covers are also provided to prevent injuries from falls and to discourage children and animals from entering the wells and becoming injured or trapped [72].

• Defensible space: The selection, location, grouping, and maintenance of vegetation on the property in such a manner that the opportunity for a fire to burn directly to a structure is minimized [73].

No standard or tested assemblies exist for lightwells installed in the WUI.

None identified at time of publication.

There are currently no requirements in adopted codes and standards that address window/lightwells.

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Replace combustible lightwells and associated combustible covers (e.g., polycarbonate plastic or fiber glass) with noncombustible materials or minimum 1/8” noncombustible, non-corrosive screening.
• Maintain areas in and around lightwells to be clear of debris and combustible materials.
• Do not store combustible items, such as firewood, in a lightwell.
• Provide a lightwell cover, constructed of noncombustible material to limit build-up of debris in the lightwell. This may not be advisable if the window well is provided for egress purposes.
• Where a mesh/screen cover is provided, clean vents on a regular basis to minimize buildup of debris in the mesh.
• Provide a minimum of 6” noncombustible vertical separation between the bottom of the lightwell and the siding/exterior wall.

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• No codes or standards related to the appropriate design, installation, and material selection of lightwells in the Wildland-Urban Interface.
• Wildfire home hardening guidance does not mention material selection or design of lightwells.
• Manufacturers do not have specific guidance for homeowners installing lightwells on their property in the Wildland-Urban Interface.
• No research has been conducted related to lightwell performance and impact in a wildfire.

• National Fire Protection Association (NFPA)
  • 1144 Standard for Reducing Structure Ignition Hazards from Wildland Fire: 5.6.4. Exterior vertical walls
• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf

The foundation of a building is often the first area to meet a spreading wildfire, as it the closest part of the structure to the ground. Debris can easily accumulate at the base of the foundation, which can be ignited by embers and surface fuels fires. These embers can ignite combustible foundation and siding, penetrate crawlspace vents, and breach basement windows [6]. Where the underside of the first floor is supported by pile or piers of combustible construction (i.e., timber), direct flaming impingement and/or embers could ignite the structure and lead to structural instability and damage.

• Basement Foundation: Full basement foundations cover the building's perimeter and are typically constructed of poured concreted walls and footing approximately 6-8' below ground level. Full basements can either be finished or unfinished. Finished basements are insulated and installed with drywall and flooring, providing living and storage space. Unfinished basements are usually not insulated, and their walls and floors are left bare [74].

• Crawl Space Foundation: Crawl space foundations are elevated several feet off footings, leaving a small, protected space (usually 3' or 4') between the ground and base of the building. The foundation walls are built partially underground and shorter than basement foundation walls [74]. They are shallower than full basements.

• Open Foundations (e.g., pier & pilings, post, caissons, or stilts foundation): A foundation that includes openings beneath the structure, such as an open crawl space or similar open areas below the ground floor construction. They typically stand several feet above the ground.

• Shallow Foundation: An enlarged base (in the plan area) for the support of the columns or walls of the superstructure in order to spread the stresses of the columns or walls onto a wider founding stratum without failure [75]. Shallow foundations can further be categorized as raft, mat, or slab-on-grade foundations and are useful in controlling differential settlement over low-bearing capacity soil.

• Wall Footing: A wall footing is a continuous strip of concrete that serves to spread the weight of a load-bearing wall across an area of soil [76].

The fire resistance rating of foundation structural elements is determined by the construction type of the building.

The fire resistance of structural elements and systems is defined by ASTM E119 or UL 263 Standard Test Methods for Fire Tests of Building Construction and Materials. This test standard is applicable to assemblies of masonry units and to composite assemblies of structural materials for buildings, including loadbearing walls and partitions, columns, girders, beams, slabs, and composite slab and beam assemblies for floors and roofs (inclusive of foundations) [48].

The standard is used to measure and describe the response of materials, products, or assemblies to heat and flame under controlled conditions, but does not by itself incorporate all factors required for fire hazard or fire risk assessment of the materials, products, or assemblies under actual fire conditions [48]. This is due to limitations of the size of the specimens tested, size of the furnace, standard fire exposure, etc. However, the test standard is one of the most widely adopted methods for comparing the performance of building construction materials, elements, and assemblies to a standard fire exposure.

The test method includes measurements of exposed and unexposed surface temperature, as well as the ability of an element or assembly to maintain structural stability, integrity, and insulation when exposed to a severe, standard fire exposure. The standard fire exposure simulates severe interior building fire conditions during flashover conditions. Depending on how the floor assembly performs against the performance criteria for stability, integrity, and insulation, the structural element can achieve anywhere from a 1-hour up to a 4-hour fire resistance rating.

• ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials: https://www.astm.org/e0119-20.html
• UL 263 Fire Tests of Building Construction and Materials: https://global.ihs.com/doc_detail.cfm?document_name=UL%20263&item_s_key=00097028

• 2024 International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC):
  • Section 707A.3.1 Extent of exterior wall covering shall extend from the top of the foundation to the roof
  • Section 602 Construction Classification
  • Section 703 Fire Resistance Ratings and Fire Tests
• 2022 NFPA 1140 Standard for Wildland Fire Protection: 25.6.4 Exterior vertical walls

• Where possible, provide at least 6” of vertical clearance of noncombustible materials along the exterior wall from the ground to the siding. Note that this minimum assumes a 5' ember resistant zone around the building.
• Maintain a 5' ember resistant zone around the building by clearing debris, dead vegetation, and any combustible items within this zone.
• Repair damage to foundation and fill in any gaps at joints with firestopping to minimize embers intrusion.
• Where an existing building has an open foundation:
  • Where possible, open foundations should be enclosed to remove the opportunity for debris, vegetation, and combustible items from accumulating under the building.
  • Remove any combustible items under the structure, and keep it clear of debris, vegetation, and storage.
  • Protect the underside of the floor structure and supporting structure with fire-rated, noncombustible, or fire-resistant materials.
  • Provide noncombustible skirting to help reduce the accumulation of debris under the building (1/16” wire mesh).

None identified at time of publication.

• Minimal guidance related to the design, material selection and maintenance of foundation walls in the Wildland-Urban Interface.
• Minimal guidance related to mitigation options for open foundation configurations in the Wildland-Urban Interface.

• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
    • Fact Sheet #7, Exterior Walls, for guidance on walls and wall coverings
    • Fact Sheet #8, Vents, for guidance on crawlspace vents
    • Fact Sheet #10, Windows and Skylights, for guidance on windows
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf
• UC Extension, Agriculture, Biotechnology & Natural Resources - http://www.readyforwildfire.org/wp-content/uploads/Wildfire_Home_Retrfit_Guide-1.26.21.pdf

Fences can become hazardous in the event of a wildfire, particularly if they connect directly to a structure. Typical wooden post-and-board fences can provide a “wick” leading directly to the structure. These fences also have ledges or spaces between components that can allow embers to collect [65]. The bottom of fences also collect debris that, when combined with combustible fencing, can become a fuel source to carry fire directly to the structure and ignite the building through radiant heat, convective heat, or direct flame contact [6]. This is further supported by a recent NIST study that found that when combustible objects burn in close proximity to fences, fire hazards are disproportionately higher [2]. There are also several case studies performed by NIST that have identified fences and mulch as common contributors to fire spread within communities [17], [81], [82]. Since fences are often just below the eaves of a house, there is the potential to carry the fire up to the eaves and thus to the roof. Additionally, fences can also create access problems for fire crews trying to enter a yard during an emergency.

• Non-combustible: In building construction material, noncombustible means one of the following:
  • Material of which no part will ignite and burn when subjected to fire. Any material passing ASTM E136 will be considered noncombustible [83].
  • Material having a structural base of noncombustible material as defined above, with a surfacing material not over 1/8” thick which has a flame-spread index of 50 or less [83].

None identified at time of publication.

There are no test standards for fencing assemblies.

• 2024 International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC): No explicit requirements
• 2022 NFPA 1140 Standard for Wildland Fire Protection: Section 25.6.3 Appendages and Projections

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• If practical, replace combustible fences using noncombustible or ignition-resistant materials (e.g., fire retardant treated lumber for exterior exposure). Stone, decorative block, brick, precast concrete, and steel are all noncombustible materials that can be used to construct visually pleasing fences [65].
• If existing wood fences cannot be fully replaced, replace the portion of the fence within 5' from the building with noncombustible materials (e.g., a metal gate that is attached to the fence on one side and to the exterior siding on the other side). Fences parallel to the home should also be constructed of noncombustible materials if a single fence is within 10' of exterior walls [65]
• Remove combustible materials such as trash bins, firewood, mulch, or other combustible materials against the fence. Ensure that all combustible components are at least 5' from the building to prevent heat and flames from igniting the building [6].
• Remove combustible mulch near fences and replace with noncombustible mulch, gravel, or other similar material.
• Remove debris and dead vegetation at the bottom of fences.
• Remove plants where the fence is being used as a trellis as it creates and traps ignitable vegetative debris. Any grass along the fence line should be regularly trimmed.
• Ensure the fence or gate is not an access problem for fire crews.
• Maintain physical condition of fence and replace any damaged, deteriorated components.
• Back-to-back fencing along either side of a property line should not be used [65].

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Fire testing and standards do not exist for fencing installed in the Wildland-Urban Interface.
• Design and installation guidelines do not exist for fencing in the Wildland-Urban Interface.

• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones, Technical Fact Sheet No. 14 - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
  • Mitigation Assessment Team Report: Marshall Fire Building Performance, Observations, Recommendations, and Technical Guidance (FEMA P-2320) - https://www.fema.gov/sites/default/files/documents/fema_p2320-marshall-fire-mAT-report-without-appendices.pdf
  • Decreasing Risk of Structure-to-Structure Fire Spread in a Wildfire (Marshall Fire MAT) - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-decreasing-structure-fire-spread.pdf
  • Homeowner's Guide to Reducing Risk of Structure Ignition from Wildfire - https://www.fema.gov/sites/default/files/documents/fema_marshall-fire-mat-homeowners-guide-reducing-risk-structure-ignition.pdf
• National Institute of Standards and Technology (NIST)
  • Knocking Down Fences for Fire Research - https://www.nist.gov/blogs/taking-measure/knocking-down-fences-fire-research
  • Structure Vulnerability to Firebrands from Fences and Mulch - https://www.nist.gov/publications/structure-vulnerability-firebrands-fences-and-mulch
  • Effects of Wind Speed and Angle on Fire Spread along Privacy Fences - https://www.nist.gov/publications/effects-wind-speed-and-angle-fire-spread-along-privacy-fences

Attachments directly protruding from the façade of the building, such as window awnings, shades, patio covers, and canopies can pose a hazard in the event of a wildfire. These components are susceptible to both direct flame exposure and firebrand accumulation and, if combustible, can become a fuel source to carry fire directly to the structure. Awnings are often composed of fabric or other lightweight material that can be readily ignited, providing a direct flame impingement on the structure. Material selection, design, and debris clearance of these attachments are critical to mitigating the impact of wildfire.

• Awnings: A sheet of canvas or other material stretched on a frame and used to keep the sun or rain off a storefront, window, doorway, or deck [84].

• Canopy: A structure or architectural projection of rigid construction over which a covering is attached that provides weather protection, identity or decoration, and may be structurally independent or supported by attachment to a building on one end and by not less than one stanchion on the outer end [14].

• The International Building Code (IBC) provides several requirements for the fire-resistant design and construction of awnings and canopies in Section 3105.
• The frames supporting awnings can be rated to achieve a 1-hour fire resistance rating per ASTM E119.
• The materials of awnings and canopies can be classified based on their performance to NFPA 701, or their flame spread index per ASTM E84 or UL 723 or performance to NFPA 286.

Note: There is no wildfire specific fire classification or rating.

Currently, there are no wildfire specific fire test standards to assess the performance of awnings, covers, or shades to embers. The following fire test standards are based on standard interior building fire exposures.

• ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials: https://www.astm.org/e0119-20.html
• UL 263 Fire Tests of Building Construction and Materials: https://global.ihs.com/doc_detail.cfm?document_name=UL%20263&item_s_key=00097028
• ASTM E84 Standard Test Methods for Surface Burning Characteristics of Building Materials
• UL 723 Test for Surface Burning Characteristics of Building Materials
• NFPA 268 Standard Test Method for Determining Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source: https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=268
• NFPA 701 Standard Methods of Fire Tests for Flame Propagation of Textiles and Films: https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=701

• 2024 International Building Code (IBC): Section 3105 Awnings and Canopies
• 2024 International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC): Section 3105 Awnings and Canopies (not strictly for WUI)
• 2022 NFPA 1140 Standard for Wildland Fire Protection: Section 25.4 Overhanging Projections

• Attached canopies/awnings can either be attached to a building or can also be mounted on the ground by the support of posts. Retractable canopies are popular as a space-saving solution.
• Freestanding, portable, umbrella shades may also be used.
• Material selection: Awnings or canopies are typically constructed of fabric, wood, polycarbonate, or metal.
• Combustible materials: Fabrics, including canvas, vinyl, and acrylic are typically the cheaper option, with easier installation. In addition, wood or polycarbonate materials may be used. These materials are combustible and should be avoided in the WUI.
• Noncombustible or ignition-resistant materials: Metals including aluminum, steel, and copper provide a more durable option. Due to the weight of the components, it is typically more costly, and requires professional installation. Metal coverings are suggested in the WUI.

• Ensure awnings and canopy materials consist of Class A flame spread per ASTM E84 or satisfy other alternative specified in Section 3105 of the IBC.
• Keep all awnings and canopies clear of debris and vegetation. Remove needles and leaf litter accumulation on or around the covering or retractable mechanism.
• Do not place or store combustible materials under coverings [11].
• Repair damage to awnings and canopies to reduce the accumulation of embers and firebrands between damaged materials.
• Where any gaps or holes are presented at the attachment points to the structure, provide with appropriate firestopping and fire caulking.

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms

• Currently, there are no wildfire specific fire test standards to assess the performance of awnings, covers, or shades to embers.
• The contribution of awnings and canopies to the vulnerability of homes to wildfire threats is uncertain.
• Relative benefit of removing or retracting awnings and canopies during preparations for a wildfire is unknown.

None identified at time of publication.

Interior building fire sprinkler systems are not effective under significant exterior exposure and typically do not provide protection to exterior construction elements. Potential functions of exterior sprinkler systems that may be intended include the control of embers landing adjacent to the protected structure and/or reduction of radiant energy from adjacent wildland or building fire exposure. The latter function would require a higher level of water delivery than control of embers.

There is no widely accepted design standard for exterior sprinklers with respect to wildland fire exposure or guidance for extension of interior residential fire sprinkler systems to protect exterior portions of a structure. Available exterior exposure protection sprinkler system information and criteria is based on building-to-building exposures and is not relevant to residential wildfire exposure. Other main concerns with exterior sprinkler protection in wildland fire applications include:

• Lack of widely accepted fire test standards, design criteria, and performance specifications for the sprinkler system (e.g., design area, flow rates, duration), water supplies (e.g., robustness of water supply, duration, source), activation method (e.g., manual, detection device), etc., for the range of scenarios that may occur during a wildfire incident.

• Due to the lack of testing, the effectiveness of an exterior sprinkler system is uncertain for the range of potential exposure types (e.g., radiation, convection, hot gases, embers) from the wildfire or adjacent structures on fire with a range of exposure durations and extended intensities.

• A municipal water source may not provide sufficient water flow and pressure during a wildfire, particularly as first responders will likely be drawing from the same system. Water supplies dependent on pumps may also be rendered ineffective during wildfire incidents when power can typically be lost due to the wildfire incident. Additionally, extensive adoption of automatic exterior exposure sprinklers for residences could present a concern for overall water supply in affected areas for firefighting operations if widely adopted by homeowners.

• The most threatening wildfires occur during high-wind events. Exterior sprinkler systems in high-wind conditions may not be effective at protecting the desired asset due to the uncertain distribution/transport of water droplets as well as evaporative losses.

• Reliable system activation is also questionable in terms of the appropriate approach, technology, and associated needs for independent and reliable power supply.

• Exterior Sprinkler: A sprinkler, either deployable or fixed, on the structure that operates independent of human interaction to douse the structure, portions of the structure, and/or surrounding vegetation with water. They can be placed on top of the roof, in the under eave area, or on the property with spray towards the building.

• Non-Residential Fire Sprinkler System: An in-building sprinkler system that meets the requirements of NFPA 13.

• Residential Fire Sprinkler System: An in-home sprinkler system that meets the requirements of NFPA 13D or 13R.

• Sprinkler, Automatic: A water spray device that is designed to provide fire protection automatically, based on either heat-activated operation or separate detection, releasing, and/or control.

• Sprinkler, Manual: A water spray device that is intended to provide fire protection when manually deployed and supplied with water under pressure.

None identified at time of publication.

None that are specific to wildland fire applications. NFPA 13, 13D, 13R provide general automatic sprinkler design requirements.

• International Wildland-Urban Interface (IWUI) Code: No explicit requirements
• 2022 California Building Code (CBC): No explicit requirements
• NFPA 1144 Standard for Reducing Structure Ignition Hazards from Wildland Fire: No explicit requirements

Additional local requirements, policies, and programs will vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for additional wildfire codes and standards.
• Check local general plan, multi-hazard mitigation plan, zoning.
• International Residential Code (if applicable - check for wildfire amendments).

• Where an existing exposure sprinkler is provided, consult with a licensed fire protection professional or wildfire professional to assess the existing installation and provide recommendations.
• Where exposure sprinkler protection is considered, several factors must be addressed including system detection/activation methods, potential pumping systems for water pressure, potential water storage for reliability. Maximizing reliability could potentially involve providing on-site water supply/storage, pump equipment, and backup power supply for the on-site water supply equipment. A licensed fire protection professional should be involved with the design and installation of wildfire exposure sprinkler protection.
• Utilize sprinkler kits provided by agencies or use home sprinklers systems. This should NOT be considered the main line of defense, as exterior sprinklers systems have no standard fire test, design criteria, or performance specifications to have any certainty of its reliability and performance in a wildfire event.
• Given the potential issues regarding performance, it's recommended that sprinkler use be a supplement to, and not a replacement for, already proven mitigation strategies, such as the reduction of potential fuels throughout the home ignition zones, along with removal of roof and gutter debris, and use of noncombustible and fire/ember ignition-resistant building materials and installation design details [49]. Sprinkler protection of any type does not allow for reduction or relaxation of other recommendations.

None identified at time of publication.

• There is little information on how well these systems actually perform under wildfire exposure or what system features can improve their performance.
• There is no design standard or performance criteria.

• Federal Emergency Management Agency (FEMA)
  • Home Builder's Guide to Construction in Wildfire Zones, Technical Fact Sheet No. 15 - https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
• National Fire Protection Association (NFPA)
  • Firewise Fact Sheet - https://www.nfpa.org/-/media/Files/Firewise/Fact-sheets/FirewiseFactSheetsExteriorSprinklers.ashx
• University of Wollongong
  • Research Report - Sprinkler Systems for the Protection of Buildings from Wildfire - https://ro.uow.edu.au/theses1/617/

Plants and trees located in the wildlands, man-made landscaping, or other open spaces directly surrounding a home, building, or structure¹ are all potential ignition locations and fuel sources for wildland or wildland-urban interface fires. Once ignited, vegetative fuels can burn with great intensity over a range of burn times, producing radiative and convective heat, and embers that can potentially lead to home or structure ignition. Landscape vegetation can be as combustible as wildland vegetation, and can easily spread fire from wildland vegetation to a home or structure, both horizontally via surface fuels or vertically as ladder fuels, from grasses and shrubs to low branches of trees. Presence of vegetation and man-made fuels proximate to a structure can also reduce the available space for firefighters to safely conduct operations.

Understanding and identifying the potential fire hazards that proximate vegetation can impose on the fire safety of homes or structures depends on a variety of factors. Vegetation type (e.g., woodland, shrubland, herbaceous, hardwood, conifer, agriculture), biological classification, plant characteristics, plant arrangements, purpose or use of the vegetation, local climate and fire regime, and quality of ongoing maintenance are key factors that influence expected fire performance of plants and trees (i.e., ignitability, combustibility, duration of combustion, and ember production). Due to the range and complexity of these factors, identifying and selecting a universal list of “fire-resistant” plants and trees, or “hazardous” vegetation, is challenging, generally requires local knowledge, understanding, and expertise, and is generally not recommended. See further detailed discussion below.

Note: This section focuses on inherent characteristics of plants and trees that affect flammability, while the next section covers defensible space zoning, spatial layout, and landscaping design.

Below are some practical challenges with managing vegetation at the parcel-scale:

• Factors Affecting Fire Performance: Wildland and landscaped vegetation immediately around a home, structure, or building can consist of a wide range of typologies (e.g., trees, shrubs, grasses), biological classifications (e.g., genius, species, native vs. invasive, fire-adaptive), plant characteristics (e.g., height, growth type and extent, phenology, chemical volatility), spatial arrangements, purposes (e.g., food, shade, recreation), and quality of ongoing maintenance (hydration, dead material) - all of which impact flammability or combustibility. In addition, local weather, climatic conditions, and natural fire regime also play a key role in understanding potential performance of plants and trees to wildfires. Fire regime describes “the spatial, or place-related, relationship between plants and fire, the intensity and severity of a fire, and the temporal, or timing-related, relationships between vegetation and fire: what time of year, and how often, does fire naturally occur? [85]” Understanding the local fire regime provides insight into the seasonality, severity, and nature (e.g., wind-driven) of wildfire threat, which can be used to bolster home protection (e.g., irrigating landscaping plants during the fire season fire season).

• Native vs. Non-Native: The relationship between non-native species and fire is complex. Evidence suggests that in some regions, non-native species are more hazardous compared to native species, and that post-fire invasions by non-native species can displace native vegetation and greatly reduce the amount and quality of habitat for native wildlife. This can be critical, as non-native species may not be well adapted to the local biome potentially disturbing soils, natural processes and ecological health. That said, in other regions even native species can be highly hazardous for fire. Non-native species invasions can also impact the overall fire regime of the landscape. Some non-natives have been documented to create feedbacks that amplify local fire regimes, increasing frequency or severity. However, the effects of non-native species are dependent on the plant community and can vary with site and climatic factors. Site-specific knowledge is instrumental [85], [86].

• Fire-Adaptive vs. Fire-Resistant: The terms fire-adaptive and fire-resistant are often ill-defined and can lead to misunderstandings about the plants in question. “Fire-adaptive” plants are those that have adapted to survive and live in environments with fire. They are typically classified into five different categories based on their adaptations [87], [88]:
  • Resisters, i.e., minimally damaged or consumed during moderate to low-intensity fires.
  • Sprouters, i.e., are partially or wholly consumed by fire and regrow.
  • Seeders, i.e., shed lots of seeds that sprout after a fire.
  • Invaders, i.e., take over recently burned areas.
  • Avoiders, i.e., grow in areas where fire does not normally occur.
  
  

  Fire adaptations are not mutually exclusive and do not guarantee that the plant is fire resistant or fire hazardous. “Fire-resistant” plants are those that do not readily burn or ignite from flame or other ignition sources. Common characteristics of fire-resistant plants include [89]:

  • Low amounts of volatile sap or resin materials.
  • Low chemical volatility.
  • High moisture content.
  • Succulent leaves.
  • A tendency to not accumulate dead material.
  
  

  The terms “fire-adaptive” and “fire-resistant” are not interchangeable. Fire-adaptive is an ecological term while fire resistance refers to a plant's flammability directly. Possessing certain fire adaptations does not make a plant inherently more fire resistant than a plant with different fire adaptations. Fire resistance should be evaluated through scientific testing or firsthand observations of the plant's fire performance if test data is lacking.

• Fire-resistant (“approved”) and hazardous (“prohibited") plant lists: Many jurisdictions have compiled lists of both “fire resistant / approved / recommended” and “hazardous / prohibited” plants to guide homeowners, design professionals and others in landscaping design. There are fewer recommendations for fire-resistant plants because low plant flammability is difficult to confirm without standardized testing, and plant flammability can change dramatically for some species as the plant moves from hydrated, to drought stressed, to droughted.

  
  

  The ability or inability to resist ignition is based on the physical features of the plant. While these lists are beneficial to the general public, they can be incomplete or misleading. Plant and tree performance during a fire is highly dependent on a variety of local factors that may not be relevant to other locations or biomes. Numerous factors as mentioned earlier - e.g., plant species, genus, structure, hydration, placement, location, setting, chemical composition, surface mass (i.e., how much biomass a plant produces within 6' of ground level), branching patterns, surface to volume ratio, foliage size, density, litter production and retention, maintenance practices (i.e., irrigation and trimming), weather, and weather history, influence whether a plant or tree should be considered “hazardous” or “fire resistant.” These characteristics should be verified to confirm the hazard level of a plant or tree. Due to the large variation and detailed nuances of plant flammability, combustibility and burn intensity, evaluation of plant “safety” should be conducted by an expert from a holistic and scientific perspective [90].

  
  

  Even “approved” plants can burn. Plants/trees on hazardous or prohibited lists are often invasive, contain volatile oils or resins, have waxy leaves, and accumulate litter around the plant or tree. Fire-resistant or “approved” plants are often native species, low-flammability, maintain live/healthy structure under drought, slow growing, and wind resistant. If no local recommendations are available, or if uncertainties remain, it is recommended to refer to both local ecologists and fire departments. Local ecologists or botanic gardens can generally provide detailed information about the fire relevant traits of different plants, including their response to drought and seasonal weather and how much maintenance is required to keep the plant in a state that minimizes fire hazard. Fire department personnel can often provide valuable insight on what plants present high fire hazard from their observations of field plant combustion.

• Other fuels in the built environment: There is a wide range of other types of combustible fuels that landowners or homeowners may have stored near the primary structure. This can include wood piles, propane tanks for outdoor grills, outdoor furnishings, gasoline tanks for lawnmowers, the handles of many yard tools, trash bins, vehicles, and decorative landscaping (e.g., artificial grass). The type, quantity, and characteristics of these other fuel loads range dramatically, which presents challenges in understanding the additional fire hazard, burning characteristics, and other contributions they may have during a wildfire. Refer to Section 2.1.2 Zones, Spatial Layout, and Landscape Design for details.

---

1 The guidance in Parts I and II of this handbook primarily targets “homes” such as single-family homes, duplexes and townhomes. However, majority of the concepts and recommendations are relevant to other types of “buildings” such as multi-family apartment and condo buildings, commercial buildings, industrial buildings, and “structures” such as accessory structures (e.g., sheds, gazebos, ADUs) and infrastructure (e.g., communication tower, utility infrastructure, road infrastructure). The use of the various terms - “home”, “building” and “structure” - are used interchangeably, but the intention is that the concepts hereinafter are relevant to all home, building and structure typologies.

• Biome: A large community of vegetation and wildlife adapted to a specific climate [91].

• Embers (firebrands): Burning or smoldering particles of vegetation from tree branches, parts of shrubs or chaparral, or other combustible materials (e.g., building materials) that ignite and burn during a wildfire and are carried by winds in front of the wildfire at varying distances (e.g., 1/2 to 2 miles) [13]. This creates a wind-driven fire hazard that is unique to wildfire incidents.

• Fire Regime: The concept of fire regime is used to capture the expected patterns of wildfire for a given ecosystem during a given period. This can include fire frequency, intensity, seasonality, extent (final size) and other metrics, as well as observed feedbacks or dependencies between vegetation and fire [92].

• Fire-Resistant Plants: Fire-resistant plants are those that do not readily ignite from a flame or other ignition source or do not readily sustain combustion [89]. These plants can be damaged or killed by fire; however, their foliage and stems do not significantly contribute to the fuel load and, therefore, the fire's intensity. There are several other factors that influence the fire characteristics of plants, including plant moisture content, age, total volume, dead material, and chemical content.

• Hazardous Plants: Hazardous plants are generally based on characteristics that increase ignitability, burn with high intensity, and introduce fire hazards in the landscape [1].

• Native Species: A species that is a part of the balance of nature that has developed over hundreds or thousands of years in a particular region or ecosystem. The term “Native” should always be used with a geographic qualifier [93].

• Non-Native Species: Non-native species are those that do not occur naturally in an area and are introduced as the result of deliberate or accidental human activities [94].

• Phenology: The study of the timing and cyclical patterns of events in the natural world, particularly those related to the annual life cycles of plants, animals, and other living things. These events include the budding of leaves in spring, the arrival of migratory birds, the flowering of plants, and the onset of fruit ripening. Phenology is a vital field of ecological research that helps us understand how living organisms respond to environmental cues such as day length, temperature, and rainfall, and how climate change can impact these seasonal changes [95].

• Plant Flammability: A description of how a plant burns, including how easily it ignites, how intensely it burns, and how well it sustains combustion [96]. Plants with high flammability generally ignite easily, burn with high intensity and sustain flaming combustion; however, aspects of flammability are not necessarily related - plants that ignite easily (like grass) do not typically burn with high intensity, although some do. Flammability is dependent on several characteristics of the plant, including type of leaves, moisture content, etc.

None identified at time of publication.

Currently, there are no standardized methods for determining plant flammability, ignitability, and combustibility (i.e., heat release rate), or criteria for plant and tree selection. See Section 2.1.1 Other References for available information.

• 2024 International Wildland-Urban Interface (IWUI) Code: n/a
• 2022 California Building Code (CBC): Chapter 49
  • Section 4906 Hazardous Vegetation and Fuel Management
• NFPA 1140 Standard for Wildland Fire Protection: n/a

Regulations vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for any additional requirements.
• Check local general plan, multi-hazard mitigation plan, and zoning documents for any additional requirements.
• Consult the local or state fire agency, or a qualified fire management specialist about codes, requirements, and standards related to defensible space [6].
• International Residential Code (if applicable - check for wildfire amendments).

• Plant and Tree Selection
  • Use the right plants in the right places, keeping fire, climate, and irrigation needs in mind.
  • Create separated plant islands that have similar sun, nutrient, and water needs to limit fuels continuity and maximize plant health.
• Maintenance
  • Keep landscaping free of dry and dead wood, dry grasses and leaf litter, especially near any structures.
  • Prune plants to provide horizontal and vertical space throughout and to eliminate ladder fuel conditions. A grass fire can move up into shrubs and then into trees.
  • Hydrate plants with a water-wise irrigation system. All plants will burn if not well maintained or hydrated.
  • Refer to Part III for vegetation management practices for various critical infrastructure.

• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms
• Fire Adapted Communities Learning Network: https://fireadaptednetwork.org/resource/webinar-recording-learning-exchanges-trex/
• University of Idaho - Fire Ecology and Management
  • REM 144 - Wildland Fire Management
  • FOR 326 - Fire Ecology and Management
  • FOR 433 - Fire and Fuel Modelling
  • FOR 450 - Fire Behavior
  • REM 429 - Landscape Ecology
  • GEOG 313 - Global Climate Change

• Currently, there are no standardized methods for determining plant flammability, other plant fire behavior characteristics, or criteria for landscaping plant recommendations.
• Understanding of fire ecology, fire hazards, and risks of all vegetation types is still developing.
• Comprehensive lists of fire-resistant vegetation and hazardous plant lists do not currently exist for all biomes, regions, and weather conditions. Most information is developed at the local level and can be anecdotal and possibly misleading.
• Best management practices, even for the same species of plant, can vary depending on the topography and local weather/climate conditions. Strategies used by residents and landscapers to alter influences on flammability (e.g., pruning and plant establishment methods), impacts to plant vigor versus flammability, and other landscaping objectives still need development and industry standardization [97].
• Widely used terms such as “low flammability vegetation,” “irrigated vegetation,” and others used in existing literature and guidance have no consistent definition [22].

• University of California, Agriculture and Natural Resources
  • Preparing Home Landscaping: https://ucanr.edu/sites/fire/Prepare/Landscaping/
  • Invasive Plants and Wildfires: https://anrcatalog.ucanr.edu/pdf/8397.pdf
  • Vegetation and Landscaping: https://anrcatalog.ucanr.edu/pdf/8695.pdf
  • Home Landscaping for Fire: https://anrcatalog.ucanr.edu/pdf/8695.pdf
• UCCE
  • Research Literature Review of Plant Flammability Testing, Fire-Resistant Plant Lists and Relevance of a Plant Flammability Key for Ornamental Landscape Plants in the Western States: https://ucanr.edu/sites/SaratogaHort/files/235710.pdf
• NFPA: https://www.nfpa.org/Public-Education/Fire-causes-and-risks/Wildfire/Preparing-homes-for-wildfire
• FEMA Fact Sheets: https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
• IBHS: https://disastersafety.org/wp-content/uploads/2021/08/Fire-Resistant-Landscaping-for-Your-Home.pdf
• CALFIRE, Prepare for Wildfire: https://www.readyforwildfire.org/prepare-for-wildfire/get-ready/defensible-space/
• DisasterSafety.org: https://disastersafety.org/wildfire/d-space/
• Sample Fire Resistance Plant List, CA: http://firesafesdcounty.org/wp-content/uploads/2017/05/Comprehensive-Fire-Resistant-Plant-List.pdf
• Be Ember Prepared (Video): https://www.youtube.com/watch?v=gAuhNDb963Y
• Drill, Sabrina L., Stephen L. Quarles, Valerie T. Borel, Drew Ready, Jason Casanova, John Todd, and Bill Nash. S.A.F.E Landscapes Southern California Guidebook: Sustainable and Fire-Safe Landscapes in the Wildland Urban Interface. UC Cooperative Extension, 2009. https://ucanr.edu/sites/safelandscapes/files/93415.pdf
• Etlinger, Matthew G. and Frank C. Beall . “Development of a Laboratory Protocol for Fire Performance of Landscape Plants,” International Journal of Wildland Fire 13, no. 4 (2004): 479-488. https://doi.org/10.1071/wf04039
• SelectTree: A Tree Selection Guide. https://selectree.calpoly.edu/
• Tree Care Information from International Society of Arboriculture. https://www.treesaregood.org/
• California Invasive Plant Council Landscaping Guidelines. https://www.cal-ipc.org/solutions/prevention/landscaping/dpp/
• Zouhar, K. Smith, J.K., Sutherland, S. “Chapter 2: Effects of Fire of Nonnative Invasive Plants and Invasibility of Wildland Ecosystems.” USDA Forest Service Gen. Tech. Rep. RMRS-GTR-42-vol. 6. https://www.fs.usda.gov/rm/pubs/rmrs_gtr042_6/rmrs_gtr042_6_007_032.pdf

Arguably more important than the type(s) of plants and trees is the spatial arrangement (e.g., proximity of vegetative and non-vegetative fuels to buildings, other fuels, and hazardous topographies; density and continuity of fuels), design, and maintenance of the vegetative fuels and other combustible man-made fuels immediately surrounding a home, building, or structure.² These aspects of the landscaping and use of the spaces immediately around a home or structure significantly contribute to the potential ignition of a structure whether by providing potential pathways for fire to travel directly to the home or provide receptive fuel beds for spot fires and additional sources of embers. While radiation and direct flaming from fire are important heat transfer mechanisms that can spread fire to the built environment, windborne embers are estimated to be responsible for more than 2/3 of home ignitions in the wildland-urban interface (WUI) [17]. Once burning, the structure, landscaping vegetation, or other combustible materials on the property act as both sources of heat and embers that can ignite nearby property and structures. Additionally, the presence of vegetation and man-made fuels proximate to a building can also reduce the available space for firefighters to safely conduct operations.

Understanding and identifying the potential hazards that spatial arrangement, design and maintenance of proximate vegetation and man-made fuels can impose on the fire safety of homes or structures, depends on a variety of factors. Some of the key concerns immediately surrounding a structure (0-100') include:

• Wildland vegetation (e.g., grass, brush, timber): These fuels can burn with great intensity over a range of burn times, producing radiative and convective heat, hot gases, and embers.

• Landscape/ornamental vegetation: Landscaping can consist of a wide range of managed vegetation typologies (e.g., trees, shrubs, grasses), plant characteristics (e.g., height, growth type, and extent), fire ecologies, native/non-native species, arrangements, practices, purposes (e.g., food, shade, recreation) and quality of ongoing maintenance. These plants can be as combustible as wildland vegetation and can easily spread fire from wildland vegetation to the structure, both horizontally via surface fuels and vertically, as ladder fuels from grasses and other surface fuels spread to low branches of trees.

• Fire-resistant and hazardous plant lists: See Section 2.1.1 Plant and Tree Types and Selection.

• Other fuels in the built environment: There is a wide range of other types of combustible fuel loads that landowners or homeowners may have stored near the primary structure. This can include wood piles, portable and stationary propane tanks, outdoor furnishings including cushions, lawnmowers and yard tools, trash bins, vehicles, and decorative landscaping (e.g., artificial grass and wood/bark mulch). The type, quantity, and characteristics of these other fuel loads range dramatically, which presents challenges in understanding the additional fire hazard, burning characteristics, and other contributions they may have during a wildfire.

• Outbuildings (e.g., sheds, gazebos, pergolas): Outbuildings are often composed of combustible materials, and once ignited, can contribute to structure-to-structure fire spread.

• Site Constraints (e.g., limited setbacks, less than 30' to nearby structures, less than 100' of defensible space): Most urban and suburban homes cannot achieve 100' of defensible space, let alone 30' to other structures on all yards without reaching their property line first. Current wildfire safety codes on defensible space do not provide guidance on how to achieve defensible space when various site constraints exist. These constraints can oftentimes introduce additional hazards (e.g., adjacent unmanaged vegetation, vacant lots, structure-to-structure fire spread) that are mostly outside of the control of the landowner. Some industry guidance does exist that recommends adopting “communal defensible space” concepts, enhancing defensible space requirements and/or structural hardening measures on the aspects of the buildings with limited setbacks [1]. However, this guidance is limited and does not necessarily address all forms of site constraints, construction typologies, vegetation conditions, and other practical limitations. Alternative methods, such as communal defensible space with neighbors and other structural hardening measures, are needed to address these increased risks.

---

2 The guidance in Parts I and II of this handbook primarily targets “homes” such as single-family homes, duplexes and townhomes. However, majority of the concepts and recommendations are relevant to other types of “buildings” such as multi-family apartment and condo buildings, commercial buildings, industrial buildings, and “structures” such as accessory structures (e.g., sheds, gazebos, ADUs) and infrastructure (e.g., communication tower, utility infrastructure, road infrastructure). The use of the various terms - “home”, “building” and “structure” - are used interchangeably, but the intention is that the concepts hereinafter are relevant to all home, building and structure typologies.

• Defensible Space: Defensible space is the area or space around homes and buildings where vegetation and other factors are managed for a specific distance to keep fire at a distance where it is less likely to ignite the structure. This managed area or space literally provides a “defense” against the fire to reduce the structure's exposure to flame radiation (heat), flame impingement, and ignition from firebrands (burning embers), which are considered the three principal factors in igniting a fire [99].

• Embers (Firebrands): Burning or smoldering particles of vegetation from tree branches, parts of shrubs or chaparral, or other combustible materials (e.g., building materials) that ignite and burn during a wildfire and are carried by high winds in front of the wildfire at varying distances (e.g., 1/2 to 2 miles) [13]. This creates a wind-driven fire hazard that is unique to wildfire incidents.

• Ember-Resistant Zone: The ember-resistant zone, as defined by the state of CA, is the space from 0 to 5' around the base of the structure and any decking where limited combustible fuels are permitted. In practical terms, this means to use primarily hardscaping; remove dead plant material (including on roofs, in gutters, and underneath structures); limit or relocate combustible furniture or other items; replace combustible fences, gates and other combustible non-structural attachments with non-combustible materials; relocate garbage containers, boats, RVs, and other vehicles.

• Fire-Resistant Plants: Fire-resistant plants are those that do not readily ignite from a flame or other ignition source. These plants can be damaged or killed by fire; however, their foliage and stems do not significantly contribute to the fuel load and, therefore, the fire's intensity. There are several other significant factors that influence the fire characteristics of plants, including plant moisture content, age, total volume, dead material, and chemical content. See also Section 2.1.1 Plant and Tree Types and Selection.

• Hardscape: Any non-living structures (such as fountains, benches, or gazebos) that are incorporated into a landscape [100]. For the purposes of this handbook this term also includes hard paths, paving, driveways, retaining walls, stairs, and any other landscape elements constructed of sturdy materials such as stone and concrete.

• Home Ignition Zone (HIZ): The concept of the home ignition zone was developed by retired USDA Forest Service fire scientist Jack Cohen in the late 1990s, following breakthrough experimental research into how homes ignite via radiant heat. The original definition of the HIZ included no zone divisions. California defensible space regulations, beginning in the 1960's, further developed the concept of the HIZ to include first, one (0-30'), then two (0-30' and 30-100') zones. An additional zone, the noncombustible zone (0-5'), first grew out of meetings in the early 1990's that were organized by University of Nevada CE Specialist Ed Smith and included Tahoe Basin fire officials. Living with Fire publications officially termed the zone the “noncombustible” zone. In the 2000's, the UC Cooperative Extension started advocating for use of the zone. IBHS also began advocating for the zone in the early 2010's. NFPA Firewise renamed zones when they adopted the concept in the mid 2010's [101]. CAL FIRE began to consider the convention around the year 2020. Presently, the HIZ is divided into three zones described as: the immediate zone (0-5'), intermediate zone (5-30'), and extended zone (30-100') [102]. Although variations on this concept may also be found, the HIZ generally accounts for the 0 - 100' space around a structure.

• Ladder Fuels: Surface vegetation or other fuels that allow fire to climb up from the landscape or forest floor to the tree canopy above. Common ladder fuels include tall grasses, shrubs, and tree branches, both living and dead. Non-vegetative ladder fuels include woodpiles, fenceposts, etc. The removal of ladder fuels is part of defensible space 'fire scaping' practices [103].

• Noncombustible Zone: A noncombustible zone is the space immediately around and under a structure (typically 0 - 5'), where no form of fuel load or combustible material is located. The intent is to keep fire and embers from igniting all combustible materials, including any form of vegetation, that can spread to the structure and cause ignition.

None identified at time of publication.

Currently, there are no standardized methods for determining plant flammability, other plant fire behavior characteristics, or criteria for landscaping plant recommendations. See Section 2.1.2 Other References for available information.

• International Wildland-Urban Interface (IWUI) Code: Section 603, A105.4.1 (woodpiles)
• California Building Code (CBC): Chapter 49
  • Section 4906 Hazardous Vegetation and Fuel Management
  • Section 4907 Defensible Space
• California Code of Regulations (CCR): Title 14, Section 1299
• California Assembly Bill (AB) 3074: Fire prevention: wildfire risk: defensible space: ember-resistant zones. https://leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=201920200AB3074
• California, Public Resources Code, 4291: Defensible space requirements
• NFPA 1140 Standard for Wildland Fire Protection: Sections:
  • A.25.9 (outbuildings)
  • 25.12.5 (woodpiles)
  • 25.11 (vehicle parking areas)
  • Chapter 26 (fuel modification area)

Codes and standards vary depending on location and adoption in individual jurisdictions.

• Check local, county, and state amendments for any additional requirements.
• Check local general plan, multi-hazard mitigation plan, and zoning documents for any additional requirements.
• Consult the local or state fire agency or a qualified fire management specialist about codes, requirements, and standards related to defensible space [16].
• International Residential Code (if applicable - check for wildfire amendments).

Defensible space is designed to provide a buffer between the building and the wildland, or other fuels, that surround it. It protects a structure from direct flame impingement, reduces exposure to radiant heat and ember cast, and is essential for structure survivability during wildfires. Defensible space also allows room for firefighting operations. Defensible space requirements and recommendations are typically subdivided into three zones, whereby the highest priority mitigations and most restrictive measures occur in the area closest to the structure or home [98]. The most common zones are as follows:

• Zone 0 (0 - 5') = “Ember-resistant zone” or “Immediate Zone”^*
• Zone 1 (5 - 30') = “Intermediate Zone” or “Lean, Clean, and Green Zone”
• Zone 2 (30 - 100') = “Extended Zone” or “Reduced Fuel Zone”

^*Note: California is currently in the process of developing and adopting local regulations to implement an “ember-resistant” zone within 5' of a structure or occupied dwelling located in high fire prone areas (i.e., as defined by CAL FIRE and local jurisdictions) adjoining a mountainous area, forest-covered land, brush-covered land, grass-covered land, or land that is covered with flammable materials [104].

• Design and implement defensible space.
  • Create fuel breaks surrounding the house and within the HIZ.
  • Create space vertically and horizontally via plant placement and pruning.
  • Use noncombustible mulch near the house.
  • Use hardscape and noncombustible materials around structures and to separate individual plants and groups of plants.
  • Use the right plants in the right places, keeping fire, climate, and irrigation needs in mind.
  • Create plant islands that have similar sun, nutrient, and water needs.

• Maintain landscaping.
  • Keep landscaping free of dry and dead wood, dry grasses, and leaf litter, especially near any structures.
  • Prune plants to provide horizontal and vertical space throughout and to eliminate ladder fuel conditions. A grass fire can move up into shrubs and then into trees.
  • Hydrate plants with a water-wise irrigation system. All plants will burn if not well maintained or hydrated.
  • Refer to Part III for vegetation management practices for various critical infrastructure.

• Fire Safety Research Institute (FSRI) - Structure Triage Considerations for Wildland Urban Interface Firefighting: https://training.fsri.org/course/169/structure-triage-considerations-for-wildland-urban-interface-firefighting
• NFPA - Certified Wildfire Mitigation Specialist (CWMS): https://www.nfpa.org/for-professionals/certification/cwms
• Fire Adapted Communities Learning Network: https://fireadaptednetwork.org/resource/webinar-recording-learning-exchanges-trex/
• National Wildfire Coordinating Group
  • S-190 - Introduction to Wildland Fire Behavior
  • S-290 - Intermediate Wildland Fire Behavior
  • S-390 - Introduction to Wildland Fire Behavior Calculations
  • S-490 - Advanced Fire Behavior Calculations
• University of Idaho - Fire Ecology and Management
  • REM 144 - Wildland Fire Management
  • FOR 326 - Fire Ecology and Management
  • FOR 433 - Fire and Fuel Modelling
  • FOR 450 - Fire Behavior
  • REM 429 - Landscape Ecology
  • GEOG 313 - Global Climate Change

• Currently, there are no standardized methods for determining plant flammability, or criteria for landscaping plant recommendations.
• Fire-resistant plant lists broadly lack scientific backing and are frequently based on anecdotal reports. When they do include scientific information, it is often a narrow representation of the plants' flammability. Caution should be used with existing plant lists because they are generally published and distributed without verification by local officials [108].
• Defensible space requirements and guidance are based primarily on studies of structure survivability in standardized conditions, and not necessarily across the full range of vegetative fuel types, topologies, and weather conditions. Additional separations and distance are likely needed where there will be severe weather conditions (e.g., high winds) and fire behavior (e.g., steep slopes, structure density, other urban fuels).
• Communal defensible space requirements do not currently exist and are often difficult to enforce if property owners do not have agreements or other easements that compel them to perform vegetation management/fuel treatments on adjacent properties that are within the 100' home ignition zone.
• Understanding of fire ecology, fire hazards, and risks of all vegetation types is still developing.
• Comprehensive lists of fire-resistant vegetation and hazardous plant lists do not currently exist for all biomes, regions, and weather conditions. Most information is developed at the local level and can be anecdotal and possibly misleading.
• Best management practices, even for the same species of plant, can vary depending on the topography and local weather/climate conditions. Strategies used by residents and landscapers to alter influences on flammability (e.g., pruning and plant establishment methods), impacts to plant vigor versus flammability and other landscaping objectives still need development and industry standardization [97].
• More detailed guidance and alternatives are needed to allow for variations in topography, siting of structure(s), ornamental landscaping, and exemplar fire-adapted landscape appropriate for local conditions/context.
• Site specific defensible space requirements need to be developed at the local level to account for local topography, vegetative typology, local construction practices, local weather/climate conditions, local environmental sensitive habitat requirements, etc.
• Expanded options and guidance are not readily available for how building/homeowners can offset defensible space requirements due to site restrictions (e.g., small parcel sizes, limited setbacks), no control over vegetation management practices of neighboring properties within the defensible space zones, building/housing density, etc.
• Understanding structure-to-structure fire spread and influence of building density, neighborhood layout and configuration on wildfire vulnerability, and associated mitigation measures is a current topic of research.
• Verifying the utility of fuel separation distance requirements in current building codes for wildfire applications is still developing.
• Parcel level versus neighborhood levels of defensible space are areas of further research.
• Common space or shared open space defensible space requirements.
• There are limited codes, standards, and guidance on vehicles in the home ignition zone. There is overlap between guidance related to vehicles and other flammable items such as liquid propane tanks.
• Widely used terms such as “low flammability vegetation,” “irrigated vegetation,” and others used in existing literature and guidance have no consistent definition [22].

• University of California, Agriculture and Natural Resources
  • Preparing Home Landscaping: https://ucanr.edu/sites/fire/Prepare/Landscaping/
  • Invasive Plants and Wildfires: https://anrcatalog.ucanr.edu/pdf/8397.pdf
  • Vegetation and Landscaping: https://anrcatalog.ucanr.edu/pdf/8695.pdf
  • Defending Your Home in Wildfire: https://ucanr.edu/sites/postfire/files/255137.pdf; https://anrcatalog.ucanr.edu/pdf/8322.pdf
  • Home Landscaping for Fire: https://anrcatalog.ucanr.edu/pdf/8695.pdf
• UCCE
  • Research Literature Review of Plant Flammability Testing, Fire-Resistant Plant Lists and Relevance of a Plant Flammability Key for Ornamental Landscape Plants in the Western States: https://ucanr.edu/sites/SaratogaHort/files/235710.pdf
• NFPA: https://www.nfpa.org/Public-Education/Fire-causes-and-risks/Wildfire/Preparing-homes-for-wildfire
• FEMA Fact Sheets: https://www.govinfo.gov/content/pkg/GOVPUB-HS5-PURL-gpo60104/pdf/GOVPUB-HS5-PURL-gpo60104.pdf
• IBHS: https://disastersafety.org/wp-content/uploads/2021/08/Fire-Resistant-Landscaping-for-Your-Home.pdf
• CALFIRE, Prepare for Wildfire: https://www.readyforwildfire.org/prepare-for-wildfire/get-ready/defensible-space/
• DisasterSafety.org: https://disastersafety.org/wildfire/d-space/
• Sample Fire Resistance Plant List, CA: http://firesafesdcounty.org/wp-content/uploads/2017/05/Comprehensive-Fire-Resistant-Plant-List.pdf
• Be Ember Prepared (Video): https://www.youtube.com/watch?v=gAuhNDb963Y
• Maranghides, Alex, and William Mell. "A Case Study of a Community Affected by the Witch and Guejito Fires." NIST Technical Note, no. 1635 (2009). https://doi.org/10.6028/NIST.TN.1635
• Drill, Sabrina L., Stephen L. Quarles, Valerie T. Borel, Drew Ready, Jason Casanova, John Todd, and Bill Nash. S.A.F.E Landscapes Southern California Guidebook: Sustainable and Fire-Safe Landscapes in the Wildland Urban Interface. UC Cooperative Extension, 2009. https://ucanr.edu/sites/safelandscapes/files/93415.pdf
• Zipperer, Wayne, Alan Long, Brian Hinton, Alexander Maraghides, and William Mell. “Mulch Flammability,” Proceedings: Emerging Issues Along Urban-Rural Interfaces II: Linking Land-Use Science and Society, 192-195 (2007). https://www.fs.usda.gov/research/treesearch/31510
• Etlinger, Matthew G. and Frank C. Beall. “Development of a Laboratory Protocol for Fire Performance of Landscape Plants,” International Journal of Wildland Fire 13, no. 4 (2004): 479-488. https://doi.org/10.1071/wf04039
• Quarles, Stephen and Ed Smith. The Combustibility of Landscape Mulches. Reno: University of Nevada Cooperative Extension, 2011. http://firesafesdcounty.org/wp-content/uploads/2017/05/The-Combustibility-of-Landscape-Mulches.pdf
• Beyler, Craig, Josh Dinaburg, and Chris Mealy. “Development of Test Methods for Assessing the Fire Hazards of Landscaping Mulch,” Fire Technology 50, no. 1 (2014): 39-60. https://doi.org/10.1007/s10694-012-0264-y

Part III of the Handbook provides a general framework with guidance and strategies to help reduce and/or mitigate hazards that contribute to wildfire risk in the WUI at the neighborhood and community scales. Planning for wildfire at these scales is a critical priority due to ongoing increases in (1) the breadth, depth, and severity of wildfire impacts in the built and natural environments; (2) continued expansion of human development into high fire hazard areas; and (3) the effects of changing climate on environmental settings.

Wildfire hazard, risk, and mitigation concepts and strategies presented in this chapter are for new and existing communities and are based on a combination of published literature, research, model codes, best practices, case studies, and other data from hazard mitigation, wildfire, forestry, engineering, planning, and related professional fields of practice. The goal of these strategies is to limit the risks to life safety, property protection, environmental services, and other values and assets in the natural and built environments. As such, the information and guidance are interrelated with key concepts and provisions at the building and parcel-scales provided in Parts I and II.

Many topics discussed in this chapter are integrally connected to decisions that occur within the wider lens of community planning and land use regulations, which determine where and how land is planned, developed, regulated, protected, or conserved to achieve long-term desired outcomes. Engaging in a thoughtful community planning process yields a range of benefits, including creating a local vision for future growth, aligning services and public safety needs, and proactively avoiding the consequences of unmanaged growth. Taking a holistic approach that integrates WUI planning within a broader planning and regulatory framework can help maximize these benefits [109].

The American Planning Association's report “Planning the Wildland-Urban Interface” can help users learn more about the concepts of WUI planning and its relationship to community plans and regulations. This document highlights collaboration opportunities for local stakeholders and offers case studies from communities [109].

Successful development and implementation of WUI planning strategies at neighborhood and community scales also requires a multidisciplinary and collaborative approach. Many interests pertain to the WUI and, as a result, many stakeholders often wish to be engaged in WUI outcomes that may have an impact on their work or residential areas. Typical stakeholders include, but are not limited to, land use planners, fire and emergency responders, architecture, engineering and urban design professionals, hazard mitigation specialists, land and resource managers, infrastructure and utility companies, business and insurance services, non-profit organizations, neighborhood/community associations, and other federal, state, or local agencies. Although some stakeholders may not engage directly in mitigation or development activities, it's important to establish a process for how groups can provide input on strategies such as regulations, mitigation programs, plan development, and policy priorities that may impact them. Leveraging the collaborative process early will build relationships and trust to support long-term buy-in and implementation [110]. Additional resources for collaboration and community engagement are available from the Fire Adapted Communities Learning Network and the U.S. Fire Administration's Fire-Adapted Communities [111], [112].

Note: This handbook is not intended to act as a code or standard, but a guidance document and reference tool. Codes referenced herein are the most recent editions at the time of development. Refer to the relevant jurisdiction(s) for adopted codes, standards, and local ordinances for statutory requirements and planning policies.

• Neighborhood: For the purpose of this handbook, neighborhood is defined as a place with physical and geographic boundaries where people share social networks, space, and other defining features such as common building typologies, shared infrastructure (e.g., roads, utility services), demographics, environmental settings, etc. [113], [114].

• Community: A socially organized population living in a physically defined locality often characterized by (a) commonality of interests, attitudes, and values; (b) a general sense of belonging to a unified, socially integrated group; and (c) some system of communication, governance, education, and commerce [115]. For the purpose of this handbook, “community” is used to represent a range of scales such as multiple neighborhoods or subdivisions, one or more master planned communities, town, district, city, or other cohesive geographic area that is larger than a single neighborhood or subdivision.

• Critical facilities and infrastructure: Critical facilities and infrastructure are the structures, facilities, systems, and networks, whether physical or virtual, that are considered essential to maintaining the normalcy of daily life and overall functionality of a community or society. As such, they are essential for the efficient functioning, and delivery, of basic services provided in cities, towns, and rural areas. According to the United Nations Office for Disaster Risk Reduction (UNISDR), California Office of Emergency Services (CAL OES) and FEMA, destruction, disruptions, or interruptions in critical facilities and infrastructure, including health and education facilities, could lead to cascading effects across sectors and sometimes across borders [116], [117], [118].

Choosing the appropriate mitigation tool(s) will vary depending upon several key considerations, including the local planning framework and whether the mitigation applies to new or existing development.

Whereas wildfire mitigation science and post-fire analysis have focused heavily on building construction and design and/or landscaping at the parcel scale, additional variables and factors can make a prescriptive approach to wildfire mitigation at the neighborhood and community scales more challenging compared to parcel and building scales, including lack of uniform development patterns, a wider range of land uses and property types, additional environmental features, and varying approaches toward land management and regulations. The effect of changing climate is a key factor that should explicitly be evaluated as it can have significant near-term and long-term impacts on the wildfire risk landscape of new and existing sites, developments and communities, and their associated capacities for resiliency. Climate change should be included in evaluations of wildfire hazards, risks, and vulnerabilities at neighborhood and community scales to understand the specific local challenges and needs for mitigation and adaptation.

Due to the potential range of factors within a community, practitioners using this portion of the handbook should consult with any applicable federal, state, or local plans, codes, and ordinances (e.g., fire codes, building codes, WUI codes, subdivision regulations, zoning ordinances) that may dictate requirements for topics addressed in this chapter. In addition, practitioners should integrate local expertise and knowledge into their mitigation recommendations to ensure it aligns with site conditions and other considerations.

Further, some mitigation strategies may be more successful when implemented through voluntary approaches, such as community outreach and education events, retrofit programs, or neighborhood chipping days. For example, existing neighborhoods who have a coordination mechanism in place (e.g., participation in the Firewise USA® program or a local HOA mitigation program) can expedite the implementation of local activities for existing properties (See Section 3.7 Examples of Neighborhood- and Community-Scale Programs). Other mitigation strategies, such as establishment of multiple access routes and adequate water supply, will be most cost-effective when introduced for new development. Finally, there may be other policy priorities to consider, such as housing needs, environmental services, public health, and economic factors, that inform the development and implementation of mitigation strategies.

A range of wildfire hazard and risk assessments can exist at local, state, and national levels. These assessments and associated maps can provide notable differences in information, terminology, analysis methodologies, inputs, and other variations, depending on the intended purpose, audience, and scale of use for which they are developed. Hazard and risk assessments can be undertaken to inform a variety of needs such as land resource management, firefighting operations, building construction requirements, regional and community planning, education and outreach, etc. These intended uses can span a broad range of audiences including fire agencies, government organizations, fire safety design and planning professionals, private sector, general public and other interested parties. In addition, the scale of analysis and scale of application can also vary from national, regional, county, city, and site-specific scales. Depending on the intended use, audience, and scale of application, the resulting outputs from hazard and risk assessments can look very different. This can present challenges and concerns of misunderstanding and misuse. For example, a national-scale fire hazard map likely provides valuable high-level information for national level decision-making but may not be appropriate (and can sometimes be erroneous) for local planning needs or firefighting operations. Examples of different hazard and risk assessments include the West Wide Wildfire Risk Assessment programs, CALFIRE's Fire Hazard Severity Zone maps, Southern Group of State Foresters, etc.

Most available wildfire hazard and risk assessments/maps are not explicitly designed to inform land-use planning, zoning, building design codes and standards, or other wildfire resiliency construction practices at the local, neighborhood, or building scales. California is one location where state-wide hazard maps are integrated into building and fire code requirements (California Building Code, Chapter 7A), and therefore directly trigger wildfire-specific risk mitigation provisions for new construction. However, most states and local jurisdictions have limited or no available wildfire hazard maps to trigger planning and building safety provisions. This means that numerous buildings and new developments are potentially being planned, designed, and constructed in high fire prone areas without appropriate building fire safety provisions. Additionally, existing building stock and developments may currently be in high fire prone areas, or could be at risk in the future, due to ongoing changes in the wildfire risk landscape, climate change, and other factors. Understanding the current and future levels of risks is a major challenge that is not currently considered in land use planning (Figures 3.1 and 3.2).

• Coping Capacity: The ability of individuals, communities, organizations, and systems to manage adverse conditions, risk, or disasters using available skills and resources. The capacity to cope requires continuing awareness, resources, and good management, both in normal times as well as during disasters or adverse conditions. Coping capacities can be defined by a variety of social, technical, programmatic, economic, and other factors that contribute to the reduction of disaster risks [119].

• Disaster: A serious disruption of the functioning of a community or a society at any scale due to hazardous events interacting with conditions of exposure, vulnerability, and capacity, leading to one or more of the following: human, material, economic, and environmental losses and impacts [116], [120].

• Exposure: The situation of people, infrastructure, housing, production capacities and other tangible human assets located in hazard-prone areas. The term exposure, in a wildfire context, is often used to describe what a building, structure, or community will experience when threatened by a wildfire (i.e., embers, radiant heat, and flame contact) [109] (Figure 3.3).

• Hazard: A process, phenomenon, or human activity that may cause loss of life, injury or other health impacts, property damage, social and economic disruption, or environmental degradation. Hazards may be natural, anthropogenic, or socio-natural in origin. Each hazard is characterized by its location, intensity or magnitude, frequency, and probability[121], [122] (Figure 3.3).

• Natural Hazards: Hazards that are predominantly associated with natural processes and phenomena [121].

• Anthropogenic Hazards: Hazards that are induced entirely or predominantly by human activities and choices [121].

• Socio-natural Hazards: Hazards that are associated with a combination of natural and anthropogenic factors, including environmental degradation and climate change [121].

• Risk: The potential loss of life, injury, or destroyed or damaged assets which could occur to a system, society, or a community in a specific period of time, determined probabilistically as a function of hazard, exposure, and vulnerability [123] (Figure 3.3).

• Acceptable Risk: Also referred to as tolerable risk, is the extent to which risk is deemed acceptable or tolerable based on existing social, economic, political, cultural, technical, and environmental conditions. In engineering terms, acceptable risk is also used to assess and define the structural and non-structural measures that are needed in order to reduce possible harm to people, property, services, and systems to a chosen tolerated level, according to codes or “accepted practice”, which are based on known probabilities of hazards and other factors [122], [124].

• Wildfire Hazard Assessment: A qualitative or quantitative assessment that identifies wildfire prone areas based on natural factors such as fuel/vegetation, slope, and weather patterns that increase the likelihood of wildfire occurring [125].

• Wildfire Risk Assessment: Risk assessment identifies where wildfire is most likely to threaten something of community value, such as human life, property, natural/historic resources, or other resources of high value. Risk assessment can also include components of physical or social vulnerability such as pre-WUI code development, limited access/egress, high density housing, vulnerable populations, as well as aspects of coping capacities (e.g., fire department response time coverage, limited firefighting water supplies, limited emergency communications). As risk is the combination of hazard, exposure, and vulnerability, a high hazard location may not be high risk if there are no assets at risk. For example, a high hazard rating in an area with a low likelihood of consequences (e.g., a wildfire in an undeveloped area) could be considered low risk; whereas a medium hazard area with the potential for high consequences could be scored as high risk [125].

• Vulnerability: The conditions determined by physical, social, economic, and environmental factors or processes which increase the susceptibility of an individual, a community, assets, or systems to the impacts of hazards (Figure 3.3).

• Physical Fire Models: Solves the governing chemical and physical process associated with combustion and heat transfer. These are often developed for research purposes to better understand the fundamental phenomena. They include Computational Fluid Dynamics (CFD) models.

• Empirical Fire Models: Statistics-based models that do not capture physical processes.

• Semi-empirical Fire Models: Capture some physical aspects with simplifications.

None identified at time of publication.

Development, adoption, and enforcement of wildfire-specific building codes, fire codes and standards, as well as planning requirements will vary depending on the state and individual jurisdictions.

• Check local, county, and state regulations and amendments for any additional requirements.
• Check local general plan, local-hazard mitigation plan, community wildfire protection plan, multi-hazard mitigation plan, or zoning documents for any additional requirements.

Examples of building codes and standards:

• International Wildland-Urban Interface (IWUI) Code - Section 502.1 Fire Hazard Severity
• California Public Resources Code 4201-4204 - Fire Hazard Severity Zones
• ASTM E1355 - Standard Guide for Evaluating the Predictive Capability of Deterministic Fire Models