The technical service managers at the 1-800-NATIONAL® desk, the gypsum industry's leading source of technical information, field a variety of questions daily regarding fire resistance ratings.
Let's review some basics regarding fire-rated gypsum construction.
The term "fire-resistance" designates the ability of a laboratory-constructed assembly to contain a fire in a carefully controlled test setting for a specified period of time. Such an assembly might be a partition, a floor/ceiling, a roof/ceiling, or a protected beam or column. The degree that assemblies put together and tested under controlled laboratory conditions retard the spread of damaging heat is measured in intervals of time. For example, if a construction assembly in the laboratory adequately contains the heat for two hours and meets other requirements during the laboratory fire test, it is given a two-hour fire resistance rating.
Fire tests may be conducted at any of several recognized facilities. Partitions, floor/ceilings, roof/ceilings, beams and columns are tested in accordance with ASTM Standard E 119, Fire Tests of Building and Construction Materials. Fire-resistance ratings are based on full-scale tests under controlled conditions and are generally recognized by building code authorities and fire insurance rating bureaus.
Requirements for fire-resistance ratings are usually assigned by local building code officials based on the expected occupancy of the space. It is critical that you review plans in the bid stage to ensure that the details drawn match the referenced design numbers. If the detail drawn does not match the assembly design number as listed in the Gypsum Association Fire Resistance Design Manual, UL Fire Resistance Directory, or Factory Mutual Specification Tested Products Guide, contact the architect for a clarification.
Fire-resistant ratings represent the results of controlled laboratory tests on assemblies made of specific configuration. For that reason, National Gypsum Company cannot guarantee the performance of specific construction assemblies erected in the field. When selecting construction assemblies to meet certain fire-resistance requirements, caution must be used to insure that each component of the assembly is the one specified in the test.
Further, precaution should be taken that assembly procedure is in accordance with that of the tested assembly. Particular attention should be given to method of attachment, stud and fastener spacing, and proper staggering of joints as required in the design.
Construction of an assembly in strict accordance with the laboratory test allows you to meet the requirements of a local code authority or architect for a system having a certain fire rating. It does not guarantee that the assembly, when exposed to conditions specific to an actual fire, will perform in the same manner as in the laboratory-tested assembly.
Although fire-rated assemblies have been tested with the indicated stud depth, most code authorities will extend the fire rating to greater stud depths and heavier gages.
Building officials conduct plan review sessions with architects prior to beginning construction. After the official has approved a set of plans, he expects that the building will be constructed using the approved designs.
The approval of any given assembly is ultimately the decision of the local building code authority having jurisdiction. If you have concerns about the acceptability of any assembly, consult with your local code authority before beginning construction.
Check the FAQs page of our web site for a more complete explanation of how fire-resistance ratings work.