New answers tagged vapor-barrier
You can install insulating foam panels directly to the existing roof membrane (decking). The panels are backed with OSB wood panels (the OSB would face out/up). So basically it would be roof decking, then foam insulation, than bonded OSB wood decking. Over it all you would place roofing felt and roofing material. Check out this short video.
Vapor barrier goes on the warm side of the insulation (averaged year round) If, on average, the garage is warmer than the house, vapor barrier goes on the garage side. If, on average, it's cooler, it goes on the house side. If you rarely close the windows, you probably don't need one at all. Penetrations should be sealed with something like acoustic ...
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