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Metal roof without vapor barrier

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Kevin Bruce
4/5/2012
I built a 600 square foot cabin with a sloping 10/12 metal roof, installed on 1" X 8" purlins spaced 2-feet apart on the rafters. The metal is exposed on the inside since I did not use a vapor barrier underneath. Now I need to insulate (economically) from the inside and am confused what I should do. Closed cell foam spray seems to be a solution but is too expensive. How can I insulate from the inside with conventional bats or foam board without worrying about condensation? I have a closed ridge but did install gable vents on either end.
Todd Miller
Isaiah Industries, Inc.
4/6/2012
I would suggest the closed cell foam. Aside from that, if you can add ventilation between the insulation and the roof, that would be great. Probably above everything, though, if you can add a well sealed vapor barrier beneath the insulation (against the living space) that will be most helpful.
Eric Novotny
An informed customer is the Best Customer!
4/6/2012
You mention gable vents so I am assuming that the structure has and attic and it is vented. If that is the case, the air loss and vapor retarder needs to be on the floor of the attic, not the roof. Read up on air sealing and insulation and you need to seal up all the gaps and cracks of the attic floor, stop the air loss, and supply additional insulation. Once you do this, your condensation issue will be nil. Feel free to email or call me and I can walk you through the process. Eric

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