Fire-Resistive Construction, Part 1
By Ronald L. Geren, RA, CSI, CCS, CCCA

Editor’s Note: This is the first of a three-part series.

I once read an article by a plans examiner who wrote about a telephone conversation between a fellow examiner and a contractor. The contractor told the examiner "You know, I don't think I can get that wall built in an hour" Rather than falling to the ground in gut-wrenching laughter, the examiner calmly responded, "That's okay, go ahead and make it a two-hour wall."

The construction industry can have its funny moments at times, but the situation described above could easily have been the setup for a potential life safety problem in the future. It's obvious that the contractor didn't know the first thing about fire-resistive construction. I can use a lot of paper space writing about fire-resistive construction, but I'll focus on the basics so you'll have a better understanding of the need for fire-resistive construction.

Fire-resistive construction is that construction designed to prevent or slow the spread of fire using materials and assemblies tested for their fire-resistive properties. The 2003 International Building Code (IBC) defines fire resistance as "That property of materials or their assemblies that prevents or retards the passage of excessive heat, hot gases or flames under conditions of use."

The fire-resistance property of a material or assembly is based on time, usually in either minutes or hours. The most common method for testing materials and assemblies to determine their endurance is ASTM E 119 Standard Test Methods for Fire Tests of Building Constructio n and Materials. Similar test methods are available from the National Fire Protection Association (NFPA 251 Standard Methods of Tests of Fire Endurance of Building Construction and Materials) and Underwriters Laboratories (UL 263 Standard for Fire Tests of Building Construction and Materials). The ASTM method takes a test specimen (100 SF for walls and partitions) that is representative of the construction expected to be built in the field, and places it in a furnace. The furnace is then heated following a strict time-temperature curve that takes the heat from 0 deg F to 2,300 deg F over an 8-hour period, if required. In the case of walls and partitions, the assembly will pass if the following conditions are met within the period of time the assembly is being tested (2 hours for a 2-hour-rated wall, for example):

" Sustain applied load (for load bearing assemblies).
" Prevent the temperature on the unexposed side from reaching more than 250 deg F above initial temperature, or more than 325 deg F at any point.
" Allow no passage of flame or gases hot enough to ignite cotton waste.
Assemblies rated 1-hour and longer, must also pass the hose stream test of ASTM E 119. This test has created some obvious confusion, in that people tend to relate the test to fire fighting operations. Actually, the test is to simulate the ability of the wall to withstand the impact from falling debris. Obviously, a wall's ability to prevent or retard a fire would be severely limited if a falling object punched a hole through it.

Building codes apply minimum fire-resistance ratings to building elements based on the building's construction type. For example, the 2003 IBC requires no fire-resistance rating for any building element in Type VB construction, which is typically the standard wood frame structure. On the other end of the spectrum, Type IA noncombustible construction requires 3-hour structural frame and bearing walls, 2-hour floors, 1-1/2 hour (also called 90 minute) roofs, and no rating for nonbearing interior walls; exterior nonbearing walls are rated based on occupancy and distance from the property line. Construction types (which could be the topic of a completely separate article) are assigned based on one or more factors such as building area, building height, or occupancy groups. If you're not sure of a building's construction type, you can typically find it on the cover sheet of the drawings, or on a separate code sheet depending on the complexity of the building.

Ronald L. Geren, RA, CSI, CCS, CCCA is the specification writer and code reviewer for the Phoenix Office of Gould Evans He is a 1984 graduate of the University of Arizona, and has held various technical and managerial positions for military, state, and private agencies. To comment on this article, suggest other topics, or submit a question regarding codes, contact the author at ron.geren@gouldevans.com