Fire Safety in Timber Buildings: First European Guideline
By Birgit Östman
The first European design guide for fire safety in timber buildings has been developed that presents information for architects, engineers, educators, regulatory authorities and building industry professionals for the fire-safe use of timber structures and wood products in buildings. The guide, available in nine languages, aims to provide the highest scientific knowledge with regard to fire safety on the European level. The guide covers the use of design codes (such as Eurocode 5 Design of timber structures), European fire standards, practical guidance and examples for fire safe design and principles of performance-based fire design.
The design guide is focusing on structural fire protection by providing the latest detailed guidance on load-bearing and separating functions of timber structures under standard fire exposure. New modelling not yet included in Eurocode 5 is presented. The guide includes information on the reaction to fire performance of wood products according to the new European system. The importance of proper detailing in building design is stressed by practical solutions. Active measures of fire protection are presented as important means in fulfilling fire safety objectives.
Timber Construction
Timber has been a favoured construction material from the beginning of civilization because of its abundance, high stiffness and strength-to-weight ratios and relative simplicity with which it can be adapted to use. These days, timber products have experienced a renaissance as their environmental credentials and an industry striving for continuously lower energy and less pollution appeal to consumers in a variety of sectors, from furniture to construction. The highest forest management standards ensure the potential for a continuous, sustainable supply for the use of timber as a building material in the future. It is therefore not surprising that timber structures are becoming an important element in sustainable and economic development and thus have attracted worldwide attention in recent years.
New construction methods and design tools have made timber-framed houses an efficient construction method, offering good quality at affordable prices. Construction sites mainly utilising timber products are recognised for their quiet and dry conditions, and the completed buildings offer user-friendly, healthy and natural living environments.
Part of the Answer to the Climate Challenge
Globally, forests are an immense resource, accounting for about 30% of the Earth’s total land base. Europe has more than 1,000 million ha of forest spread over 44 countries, equivalent to 1.42 ha (more than two football pitches) per person. Recognizing the importance of wood as a naturally renewable building material is vital for meeting the challenges of climate change and ensuring a sustainable future.
Forests play a key role in mitigating climate change, as they absorb carbon dioxide from the atmosphere and store the carbon in trees and in the ground. Research shows that cultivating forests and utilising their resources benefits the environment.
Timber and Fire Safety
The combustibility of timber is a main reason that too many building regulations and standards strongly restrict the use of timber as a building material. Fire safety is an important contribution to feeling safe and an important criterion for the choice of materials for buildings. The main precondition for increased use of timber for buildings is adequate fire safety.
Worldwide, several research projects on the fire behaviour of timber structures have been conducted during the past few decades, aimed at providing basic data and information on the safe use of timber. Novel fire design concepts and models have been developed, based on extensive testing. The current improved knowledge in the area of fire design of timber structures, combined with technical measures, especially sprinkler systems and well-equipped fire services, allow safe use of timber in a wide field of applications. As a result, many countries have started to revise fire regulations to permit the greater use of timber.
Fire test and classification methods have recently been harmonised in Europe, but regulatory building requirements remain on national bases. The European standards exist on the technical level, but fire safety is governed by national legislation and is thus on the political level. National fire regulations will therefore remain, but the new European harmonisation of standards will hopefully speed up the reform of national regulations.
Major differences between European countries have been identified, both in terms of the number of storeys permitted in timber structures and of the types or amounts of visible wood surfaces in interior and exterior applications. Several countries have no specific regulations or do not limit the number of storeys in timber buildings. However, eight storeys are often used as a practical and economic limit for the use of timber structures. This limit may be higher for façades, linings and floorings, since these applications may also be used in, for example, concrete structures.
FireInTimber Project
The WoodWisdom-Net research project FireInTimber was conducted in close cooperation with 14 partners in nine European countries. The key objective was to provide new possibilities for wood products in construction through proper fire design. The use of wood products is to be supported by comprehensive and scientifically robust background data, which is presented in user-friendly and adapted tools for engineers and other stakeholders. The outcome is to facilitate simplified and quicker approval processes for wood products in buildings. This data will increase the general public’s confidence and positive perception of wood products.
The FireInTimber project has resulted in new knowledge, especially for modelling of the load-bearing capacity of new types of timber structures. The project’s results are presented in about 50 scientific papers, reports and presentations at scientific and technical conferences. The main result for a greater audience is the technical guideline Fire Safety in Timber Buildings [1]. It is the first Europe-wide guideline on the fire-safe use of wood in buildings.
Technical Guideline for Europe
The technical guideline comprises about 200 pages. Guideline summaries in nine languages are also available. The guideline chapters are summarised below.
- Chapter 1, “Timber Buildings,” introduces the established uses of timber buildings and the renaissance of timber structures in recent years as a result of the drive towards more-sustainable construction solutions.
- Chapter 2, “Fire Safety in Buildings,” discusses the basic concepts of fire safety in buildings such as fire behaviour, loads, scenarios and safety objectives. Means of fulfilling the fire safety objectives are described for use in all buildings and as a basis for the design.
- Chapter 3, “European Requirements,” presents an overview of the new European requirements for fire safety in buildings, based on the Construction Products Directive and Regulation (CPD and CPR) and their essential requirements. These requirements, which are mandatory for all European countries, include the classification systems for reaction to fire of building products, fire resistance of structural elements, external fire performance of roofs, fire protection ability of claddings and structural Eurocodes. Descriptions of how these requirements are applied to wood products and timber structures follow in later chapters.
- Chapter 4, “Wood Products as Linings, Floorings, Claddings and Façades,” presents the reaction-to-fire performance of wood products according to the new European classification system. A wide range of products is included: wood-based panels, structural timber, glued laminated timber (glulam), solid wood panelling and wood flooring. A new system for the durability of the reaction-to-fire performance of wood products is explained and put into context, as well as the recent K-class system for coverings with fire protection ability. In addition to reaction-to-fire performance, some countries have extra requirements for façade claddings, for which at present no European harmonised solution exists. Best practice and state-of the art information on fire scenarios for facades are presented.
- Chapter 5, “Separating Structures,” presents the basic requirements, calculation methods based on component additive design and the Eurocode 5 design method. It also presents an improved design method from recent research as potential input for the ongoing revision of Eurocode 5 and practical examples on how to use the method.
- Chapter 6, “Load-Bearing Timber Structures,” introduces the design methods for verification of the structural stability of timber structures in the event of fire, applying the classification for Criterion R for fire resistance (load-bearing function). Reference is made to Eurocode 5 with respect to charring and strength and stiffness parameters. Alternative design models are presented as well as new design methods for timber structures currently outside the scope of the present Eurocode 5.
- Chapter 7, “Timber Connections,” provides an overview of the basic requirements for timber connections. The calculation methods in Eurocode 5 are complemented with state-of-the art design methods, the result of recent research. Both timber-to-timber and steel-to-timber connections are included. The models are described and worked examples presented.
- Chapter 8, “Fire Stops, Service Installations and Detailing in Timber Structures,” deals with the need for adequate detailing in the building structure to prevent fire spread within the building elements to other parts of the building. Special attention is paid to basic principles, fire stops, element joints and building services installations. Several practical examples of detailing in timber structures are included.
- Chapter 9, “Novel Products and Their Implementation,” is aimed primarily at product developers. It describes guidelines for introducing novel structural materials and products. The basic performance requirements and potential solutions for insulating materials, encasing claddings and fire-retardant wood products are included. The innovation process from idea to approved product ready for the market is outlined.
- Chapter 10, “Active Fire Protection,” describes how such protection is used to achieve a more flexible fire safety design of buildings and an acceptable level of fire safety in large or complex buildings. The chapter introduces common active fire protection systems, such as fire suppression and smoke control systems. Sprinkler installation provides special benefits for increased use of wood in buildings, particularly where surfaces are to remain visible.
- Chapter 11, “Performance-Based Design,” describes the basic principles of performance-based design, requirements and verification. Fire risk assessment principles are described in terms of objectives, fire safety engineering design, design fires, calculation or simulation methods and statistics. A case study of a probabilistic approach is included.
- Chapter 12, “Quality of Construction Workmanship and Inspection,” describes the need for execution and control of workmanship to ensure that the planned fire safety precautions are built in. It also emphasizes the need for fire safety at building sites, when not all fire safety measures are yet in place.
Acknowledgement
The design guide has been developed in the European research project FireInTimber (Fire Resistance of Innovative Timber structures). Leading experts and researchers from nine European countries have been participating and guarantee its quality and relevance. Research partners are SP Trätek (now SP Wood Building Technology) Sweden (coordinator); VTT Finland; Munich Technical University and DGfH Germany; Blaise Pascal University and CSTB France; Wood Centre Norway; Building Research Establishment UK; Holzforschung Austria; Innsbruck University and Vienna Technical University Austria; ETH Switzerland and Resand Estonia.
The supporting public funding organisation is the WoodWisdom-Net Research Programme jointly funded by national funding organizations in the participating countries. The main supporting industry partner is the European wood industry represented by Building With Wood within CEI Bois.
Birgit Östman is with SP Wood Building Technology, Stockholm, Sweden
Reference
- Science Technical Research Institute of Sweden, “Fire Safety in Timber Buildings – Technical Guideline for Europe” SP Report 19 (2010). www.sp.se/FSITB