How many fasteners are needed to achieve FMRC I-60 or I-90 for 1/2″ or 5/8″ DensDeck when used as an underlayment directly over a steel deck?
To achieve an FM I-60 wind uplift resistance for 1/2″ and 5/8″ DensDeck when applied directly to a steel deck, use eight fasteners per 4′ x 8′ panel and 12 fasteners per 4′ x 8′ sheet for corner panels. To achieve FMRC Class I-90, eight fasteners for field panels and 12 fasteners for corner panels and all perimeter panels are needed. A Factory Mutual Research Corporation (FMRC) Class 1 rating means that the system qualifies for the lowest insurance rates by FM-affiliated insurance companies. Systems that don’t pass the Class 1 criteria are rated FM Class 2. Class 2 garners a higher insurance premium. FM uses a calorimeter test to classify systems as Class 1 or 2. (A calorie is a unit of heat energy.) In case of fire, 1/2″ and 5/8″ DensDeck applied directly to a steel deck will not let excessive heat escape to roof insulation and other components, which limits the damage. The numbers 60 and 90 are not wind velocities. They represent 60 and 90 pounds per square foot (psi) of negative for
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