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TOPIC: I Have An Existing Metal Roof and Have A Question

Roof insulation

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I have an a frame cabin with 2 inch tongue and groove decking with metal on top. There is no way to insulate the inside. I want to foam the outside. I can't get consistent answers on how to do it. I would like to remove the metal, put something over the wood, build a 2x4 frame, foam the cavity with closed cell foam, put osb decking on the frame work and put the metal back on. What kind of under lament should I use? Do I need any venting? I need some suggestions,
Guest User

3/23/2015
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It sounds like what you're building will not require venting. That said, venting and a thermal break in the system would only be helpful, not harmful. I would suggest a layer of quality synthetic underlayment, or whatever the roofing manufacturer requires. Todd Miller
Todd Miller
Isaiah Industries, Inc.

3/23/2015
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So if I remove the existing roof, put an under lament, shark skin or similar. Then build the frame work with 2x4, foam the cavity full (3 1/2) inches, with closed cell. Put osb decking felt paper or ?, then put the metal back. Would that work?
Guest User

3/23/2015
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The underlayment I was referring to would be on top of the decking, directly beneath the roofing. What you are referring to would be more of a vapor barrier. Installing a vapor barrier would not be a bad idea. I would probably do an impermeable vapor barrier for that rather than a roofing underlayment through. Todd Miller
Todd Miller
Isaiah Industries, Inc.

3/23/2015
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Why not just use rigid foam over the roof sheathing? This type of system is fine. You can air seal the T&G boards by just putting peal and stick membrane over it. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

3/23/2015
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