Foam Plastics

IBC Chapter 35, IBC 2603.4.1.5, 1508.1, and 1502.1 – 7/31/2008 

Can foam plastic insulation be used as one of the components within a roof assembly without the thermal barrier referenced in IBC section 2603.4.1.5 if the roof assembly has been tested and listed as FM Class 1, even if the testing was to FM 4470 instead of FM 4450?

Yes. The purpose of the thermal barrier is to prevent the foam plastic from becoming involved in the early stages of a fire within the building below. The Class 1 fire classification indicates that the assembly will not self-propagate if exposed to a localized fire exposure from the underside of the deck. That determination is based on Factory Mutual’s construction materials calorimeter test, the test that is included as a part of both FM 4450 and FM 4470. If the roof assembly fails that part of the test, the roof assembly cannot be fire classified as Class 1.