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Old 04-19-2014, 05:08 PM   #1
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Should polyiso be taped?


A number of homes up here are retrofitted with rigid polyiso, and the local box store told me that there is concern that these panels were taped at the seams when they shouldnt of been. He said that the foil on the panels when taped acts as a second vapour barrier, trapping in moisture. Makes sense. Im sure you would lose some r value by not taping, curious if you would have higher r value with untaped polyiso, or taped XPS, of the same thickness?
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Old 04-20-2014, 11:08 AM   #2
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What do they think the foil barrier is? How thick of insulation are we talking in this retrofit? If the seams aren't sealed, you can get air leakage. If it's being installed on a house, the walls should have been checked for a vapour barrier. That said, you're in northern Ontario, vapour barrier is usually always installed inside. Should it be installed if you add a lot of insulation to the outside? IMHO, no, but depending on your AHJ, they may or may not understand why. In my area, it's easier to put up the barrier for inspection, then rip it down when its passed than to explain why you don't need it. In this case, I think the box store employee is partially right but not taping the seams isn't going to help the drying potential, if there is a problem
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Old 04-22-2014, 09:56 PM   #3
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Risky to use foil-faced and poly... the FB needs to be thick enough for local temps per location to prevent cavity condensation of any moisture from interior/exterior, as said; http://www.buildingscience.com/docum...nsulation/view

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