Although IBC Section 1505 refers to testing of "roof assemblies and roof coverings," the testing is really only applicable to the roof covering. ASTM E108 and UL 790 are the two tests mentioned in the IBC. They are both nearly identical. The roofing membrane, shingles, shakes, tiles, panels, and coatings are tested over either a combustible (i.e., wood) substrate or a noncombustible (i.e., metal, gypsum, or concrete) substrate. Manufacturers would most likely test their roof coverings using a combustible substrate, which would allow many different types of installations. For example, if you plan on installing a TPO membrane over polyisocyanurate board insulation ("polyiso") on a metal deck, then it would be a combustible substrate since the polyiso is combustible.
A roof covering fails a test when any part of the combustible deck is exposed. Thus, if a TPO membrane over a wood deck is exposed during a test, it would be no different if the TPO membrane failed over a polyiso substrate.
Therefore, entire roof assemblies are not tested. Roofing components such as substrate boards, insulation, underlayments, and cover boards, are not included in the tests. If a membrane requires installation over a noncombustible substrate, then a cement or gypsum cover board will be required over the insulation.
Other components of the roof assembly must comply with other parts of the IBC, predominantly Section 1507. Foam insulation used in roofing must comply with IBC Section 2603.6, which points back to Sections 2603.2, 2603.3, and 2603.4. The problem here is that it states "provided that the assembly with the foam plastic insulation is a Class A, B, or C roofing assembly where tested in accordance with ASTM E108 or UL 790." The tests I have seen (and the test specimen requirements in the standards themselves) do not include foam insulation. The fact remains: if the roof covering is breached over a combustible deck, it fails the test.
