Modern construction codes owe much of their heritage to the shared experience gained over the past century. The major growth and development within the construction industry and the changes in construction technology all have formed the basis for expectations regarding building safety. Designers, developers, owners, and the public have used that knowledge base to foster the development and adoption of modern building codes that establish an acceptable baseline used to measure the standard for safety in buildings.
Over the last 15 years, several new building codes have emerged. The process of developing these codes offered a unique opportunity to reexamine each and every provision in each and every code, using the combined experience from the entire construction industry. Their collective experience and perspective formed the basis for the resulting tools that have been joined together and are now the minimum requirement in the codes.
Balance, and Height and Area Tables
Balance between passive and active fire protection systems and the impact on building height and area has been the focus of code changes at ICC and Technical Committee work at NFPA for the past five years. Recognition of a balance in building height and area is not a new issue. It was a question that was being answered as part of even earlier modern codes.
The 1927 edition of the Uniform Building Code (UBC) and the 1934 edition of Building Code Recommended by The National Board of Fire Underwriters both included allowances for increases in building areas when the building was protected by a sprinkler system.
This allowance for additional area facilitates the use of less-restrictive types of construction, thus establishing a balance between the increased use of an active fire sprinkler safety system against a passive fire resistance rating. Such "trade-offs" for sprinklers began the process of integrating more and more active fire protection in structures and providing allowances for less fire resistance. Continuous evolution of the codes developed more explicit criteria for various materials and systems that are designed specifically to address identifiable problems and issues within these buildings. Active fire protection systems were originally designed to assist firefighters to extinguish a fire.
The emphasis of the early National Building Code was on the Fire-Resistive Type A and Type B building construction. A typical unprotected steel frame office building would have been limited to 18,000 sf. (1,700 m2) in area and 35 ft (11 m) in height. To be considered a Fire-Resistive Type A or Type B building, the columns would be required to have 4- or 3-hr. fire resistance, floors would have to have 3 or 2 hrs., and bearing walls would be required to have 4 or 3 hrs., respectively.
Between the early 1950s and today, changes in the codes have been rapid with significant reliance on the use of active fire protection systems and much less reliance on the passive systems. Under the current ICC, an office building of Type IIB unprotected steel frame would be limited to 4 stories in height and 23,000 sf. (2,100 m2) in area, although an overall height of any building over 55 ft (17 m) above the level of fire department vehicle access would require the installation of a sprinkler system under the current code.
The record of fire incidents and the deaths in fires have played a significant role in that change. NFPA's records on fire loss in buildings helped to support this. The National Fire Protection Association1 notes that the new number of incidents where fire suppression failed to operate is about 7 percent.
More recently, it has become popular to take fire protection systems that are designed to provide protection to life and use them for property and content protection. This approach can clearly be seen in the extremely low threshold for installation of sprinklers in elementary and secondary schools. Schools designed to meet modern codes were considered relatively safe and, except for arson, free from most fire incidents, and thus did not require the installation of sprinklers. An argument was raised that such facilities have gained a higher level of importance within communities as they no longer were simply a school, but housed functions that were important far beyond a school building, which raised the value to the community it could not afford to replace. Thus, today there is a 20,000 sf. (1,900 m2) threshold for sprinklers in buildings that have a good record of life safety.
Much of the fury that surrounds the question of balance is generated by the heights and areas tables. Proposals have been forwarded to reduce the allowable areas to those in the old Uniform Building Code (UBC). Significant focus has been placed on the results of the ICC process without fully examining the way Table 503 in the International Building Code (IBC) was created.
Risk is one of the terms that are constantly thrown around as the reason for examination of how technologies of building are applied to a particular occupancy. However, it is challenging to define the term and measure its value. SFPE's draft Engineering Guide to Application of Risk Assessment in Fire Protection Design, defines "risk" as "the potential for realization of unwanted adverse consequences, considering appropriate scenarios and their associated frequencies and consequences."
NFPA 5000
Most recently, NFPA developed a second model building code (NFPA 5000) that was designed to compete with the ICC International Building Code. During the development of that code, when the question of building height and area was first breached, this author proposed that there be no limit on building height or area. The rationale was that the current standards for life safety found in NFPA 101,2 such as the travel distance, stairway enclosure, sprinkler and standpipe thresholds, finish controls, etc., along with the intrinsic structural limits on building materials, were adequate to control their use in an appropriate manner.
A special task group was set up to examine this and other height and area proposals. When NFPA 50003 was finished, the first edition contained only the traditional height and area criteria, mirroring the requirements in the International Building Code. However, for the 2006 edition of NFPA 5000,4 in addition to the traditional height and area limits, Chapter 7 will reference an appendix containing an alternate method for control of building heights and areas using traditional height limits for standard construction materials, but proposing that the area of buildings be not limited except for some of the most hazardous assembly and care occupancies. It contains two thresholds for the maximum compartment for an occupancy, based on whether the building is sprinklered or not. A typical sprinklered building can have a compartment of 60,000 sf. (5,600 m 2), and an unsprinklered building is limited to a compartment of 12,000 sf. (1,100 m2).
ICC Height and Area Development
The traditional heights and areas as now found in the IBC and NFPA 5000were derived by the work of an ICC committee of representatives from the three model codes assigned responsibility to develop such limits. Given the three divergent aproaches, not to mention the Board for Coordination of Model Codes (BCMC) approach,-the committee had to come to a single conclusion.
For example, the three model codes used the following formulas to determine the maximum allowable area per floor.
National Building Code (NBC)
Aa =(1+ Si +Fi -HR)
Standard Building Code (SBC)
Aa =TA(1+ Fi)
Uniform Building Code (UBC)
Aa =TA(Fi+ Si)
Where:
Aa is allowable area
TA is tabular area (area in the table)
Fi is the frontage increase factor
Si is the sprinkler increase factor
HR is the height reduction factor
Only the National Building Code (NBC) used a height reduction factor. The Standard Building Code (SBC) incorporated the actual area increase for sprinklered buildings directly into its tables as does NFPA 5000.
To assure that any building permitted in any of the three model codes was also permitted under the new code, ICC's committee decided to start with the largest possible building area that could be generated by each code for each occupancy and each type of construction. From this matrix, they chose to take the largest area and work backwards, removing the permitted increases to develop a tabular area. This approach required the committee to choose a single method for area increases. Rather than choosing one of the three current model codes, they chose to adopt the BCMC method. This required only an adjustment for frontage and sprinklers.
As can be seen in Table 1, for an apartment that is constructed of fire-rated wood frame construction (VA under IBC or V 111 in NFPA 5000), there were some anomalies created. The values in the tables were smoothed to provide some relative balance among the various cells. Similarly, some changes came late in the original code development process when a factor of 3 was set as an upper limit for the building area, which was not a part of the committee work.
It is almost impossible to find rational statistics that show how the model codes perform in one region of the country or another. Part of the reason is that there is no reporting of the age of a building involved in any particular incident, and whether a building was built under one of the model codes is impossible to determine. However, it is interesting to look at the statistical performance of each state and the various factors that may be involved in the fire loss history. In the latest data reported by NFPA on fire loss,5 states are ranked by average loss of life for the period of 1977 to 2001, by percentage of persons that received a 12th grade education, the percentage that smoke, and the percentage below poverty levels.
Michigan and Indiana, which both had the Uniform Building Code (UBC) for at least part of their code enforcement, are ranked 16th and 17th, and Virginia, Illinois, and Ohio, using the NBC or no model code, were ranked 19th, 21st, and 23rd overall. Each of these states had a very high percentage of smokers and a relatively high percentage of those below the poverty level. California, another state that used the UBC, has a high percentage below the poverty level, but was ranked 47th of all states in fire deaths.
The trend is for reduced fire loss across the board. The same NFPA report notes:
The most populous states, whose death tolls are large enough to permit statistically meaningful comparisons between 5-year averages, all show dramatic improvements:
- California, down 32%.
- Texas, down 33%.
- New York, down 40%.
- Florida, down 31%.
- Pennsylvania, down 30%.
- Illinois, down 39%.
- Ohio, down 39%.
- Michigan, down 30%.
Balance
NFPA was unable to offer statistical data to show any correlation between the size of a building or the type of construction and the loss of life in buildings when it developed the research background for the task group studying height and areas for NFPA 5000.
Risk and determining the means by which it is measured it are not found in the formula for determining the height and area of a building. The fundamental information available from NFPA data shows no correlation between the use of any one of the older codes. No correlation can be found between loss of life in various building types. Education, poverty, or other social factors are universally ignored by codes, even though they are recognized as playing a part in such loss.
The height and area provisions have economic as well as safety implications for a community. In addition to the costs for bricks and mortar, or in this case, the fire resistance rating of steel and concrete, costs are also found in the use of the environment and resources. Smaller allowed building areas means that more is spent to consume more land because more buildings-must be built to accommodate the same program area, and more energy is consumed to build more complicated buildings, which in turn require more energy to manage and maintain.
David S. Collins is with the Preview Group
References
- Rohr, K., and Hall, J., "U.S. Experience with Sprinklers and Other Fire Extinguishing Equipment," National Fire Protection Association, Quincy, MA, 2005.
- NFPA 101, Life Safety Code , National Fire Protection Association, Quincy, MA, 2003.
- NFPA 5000, Building Construction and Safety Code, National Fire Protection Association, Quincy, MA, 2003.
- NFPA 5000, Building Construction and Safety Code, National Fire Protection Association, Quincy, MA, 2006.
- Hall, J., "U.S. Fire Death Rates by State," National Fire Protection Association, Quincy, MA, 2004.