What is the difference between a FM Class 1 and FM Class A code approvals?
Polyiso insulation offers the most extensive range of code approvals for insulation use in roof systems. It remains the only foam plastic insulation product for direct application to steel deck to earn FM Approval for Class 1 Roof Systems. An often confusing issue is whether a “Class 1 roof” is the same as a “Class A roof”. The distinction between these types of roof classifications becomes even more critical when the roof system contains foam plastic insulation, such as polyiso, polystyrene or polyurethane. Note, all Class 1 roof assemblies are Class A roofs, but not all Class A roof systems meet Class 1. For example, while roof assemblies containing polystyrene insulation can meet Class A, there are no roof assemblies with direct-to-deck polystyrene insulation that qualify as a Class 1. The designation of “Class 1” can be granted only by FM and reflects the successful testing of the whole roof assembly using FM 4470. According to the scope of FM 4470, “because the fire performance of
