Roofing Fasteners thru Rigid Insul

Guest User
Is there an industry rule of thumb for the maximum thickness of rigid insulation for fastening metal roofing systems thru the insulation to the roof decking? The roof section scenario is metal roof decking over wood structural framing, vapor retarder (as needed), EPS insulation (i.e. Dow Deckmate) over the decking, and the metal roofing over the insulation.
Todd Miller
Isaiah Industries, Inc.
Unfortunately I do not believe there is a standard on this and, also, I do not know of any companies that have done uplift testing with this scenario. That does not mean it isn't done .... just that it is not supported heavily. Nor am I aware of any building codes that support this application. I personally am not real fond of metal installations over foam. Even rigid foam can compress some when walked on and that can be a potential issue with a metal roof. We will see what others might add. I would suggest a layer of decking over the foam before the roof is installed.
Eric Novotny
An informed customer is the Best Customer!
Always a good idea to check with local code on what is acceptable and when in question, get it signed off on. What is the current construction (vaulted or vented attic), decking (sheeting or board), and what type of metal are you going back with?

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