Exterior wall assemblies must pass NFPA test

1 year, 1 month ago

Note: The sections of the International Building Code cited below are from the 2021 edition.

The International Building Code (IBC) classifies buildings into five basic types, depending on whether the exterior and interior structures are either combustible or non-combustible. Types I, II, III, and IV all include non-combustible exterior walls. Therefore, the code regulates components located in these walls that are typically combustible, such as weather barriers (section 1402.5), plastic foam insulation (section 2603.5.5), and combustible claddings such as high-pressure decorative exterior-grade compact laminates (section 1408.10.4) and metal composite materials (section 1406.10.3).

NFPA 285 is a fire test standard that is referenced in the two aforementioned sections of the IBC, and is used to measure the potential for an exterior wall assembly to spread fire on the exterior side of a building, both horizontally and vertically. This test, and its predecessors, have been around since the 1980s. For the test, the assembly undergoing the test is constructed as it would be in the field on one side of a two-story test structure. The tested assembly has a window on the first floor. During the test the wall is subjected to fire for thirty minutes. Successful completion of the test depends on the wall assembly’s ability to limit flame spread and temperatures.

NFPA 285 is an assembly test. Therefore, all the components of the exterior wall must be tested together and comply. Individual components that were part of an approved assembly cannot be marked as passing NFPA 285. Many manufacturers have procured testing on their products and have published assemblies that pass NFPA 285. If designers elect to use a wall assembly that hasn’t undergone testing and compliance with NFPA 285 is code required, then it would need to be tested, which would add cost to the project and lengthen the schedule.

It is important to be familiar with the code requirements because there are exceptions that alleviate a combustible exterior wall assembly from compliance with NFPA 285. For example, in construction types I, II, III, and IV, exterior wall assemblies that include metal composite materials are only required to comply with NFPA 285 if the exterior wall is forty feet above grade plane (section 1406.10). Similarly, exterior walls of the aforementioned construction type that contain a combustible weather barrier do not need to comply with NFPA 285 if they are less than forty feet above grade plane or if the water-resistant barrier is the only combustible component in the wall with a facade of brick, concrete, stone, terra cotta, stucco, or steel with a prescribed thickness.

If compliance with NFPA 285 is required for a project, it is important that the designers and contractors take that into consideration when proposing alternate products in the exterior wall. Substituting just one material may cause an exterior wall assembly to lose its NFPA 285 test compliance and require testing of the proposed assembly, causing schedule delays and requiring additional project funding.

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