b'FIRE RATINGSFIRE-RESISTANCE RATING The listed assembly is usually manufac- Canada, even if the ASTM standard is Thefire-resistanceratingofaroofturer-specificsincedifferentmanufac- referenced in the project specification.assembly indicates its resistance to a fireturers materials will perform differently that originates from within the building.and may have different fire performanceROOF FIRE CLASSIFICATIONSuch a rating is provided to help preventcharacteristics. As mentioned previously,The roof fire classification is a qualitative a fire from spreading beyond the buildingthe two common test standards are theassessment of how well a roof surface of origin. ASTM and CAN/ULC standards. Theresists external fire exposure from a fire The fire-resistance rating of a listedCAN/ULC test results should be consid- that originated outside of the building. assemblyisdeterminedbyaratingered first due to these standards beingThisclassificationrelatestothetop agency(e.g.,UL),whotests,approvesmorerestrictiveandbeingreferencedlayers(typically theroofingmembrane andcataloguesthetestedassembly.by the national and provincial codes inandsometimestheprotectionboard) and is independent from the full roof assembly.Therooffireclassifications are determined from tests performed in accordancewiththeCAN/ULC-S107 standard, and roof surfaces are classified into the following categories:Class A: Can sustain severe fire exposure;Class B: Can sustain a moderatefire exposure; Class C: Can sustain minimal fireexposure; andUnclassified: Fails the test or hasnot been tested.This classification naturally raises the following questions: How are the fires classified? How does a severe fire differ from a moderate one? To understand the difference, it requires an understanding ofthetestingprocedure.Theroof fire classification is composed of four aspects that are evaluated. The aspects are as follows:Brand size;Exposure time; Wind simulation; and Flame spread allowed.It is not the intent for the scope of this article to go into detail about how thoseaspectsareclassified.However, it is important to note that the classi-ficationisexclusive,meaningthatif aroofassemblyisclassifiedasClass A,alltheaspectsmeettheClassA criterion of said aspect. If one of the aspects does not meet the classification, then the assembly will be classified as the next lowest class that is fully satis-fied. Meaning, if an assembly met three of the four criteria for Class A but the last criteria only met Class C, then the assembly would be classified as Class C. 20 lROOFINGBClSUMMER 2025'