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plastic sheeting over closed cell foam Post New Topic | Post Reply
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hykerob
Posted: Aug 19, 2016 03:48 PM
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plastic sheeting over closed cell foam
I'm having closed cell foam insulation sprayed between the rafters of my vaulted ceiling in NH, 5.5" thick directly to the underside of the plywood sheathing. The rafters are 2x10", so there will be a few inches of space below the foam. Do I need to install poly sheeting before installing sheet rock? One builder tells me I need poly to prevent moisture from condensing on the bottom surface of the foam. The other tells me poly will just trap any moisture in the ceiling between the poly and the foam, since there is no air flow. who is correct and is poly necessary or dangerous?Also, are there any concerns with using traditional figerglass batts (and poly) in the walls, from the roof down, and is there any special transition necessary between the fiberglass in the walls and the foam in the ceiling? I only want to do this once. thanks, Rob. |
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TSW99
Posted: May 03, 2017 08:18 PM
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The first condensing surface in the roof assembly will be the interior side of the roof deck. Since CC will be applied to the roof deck, and CC is by nature low in PERMS moisture laden air will not reach the roof deck and will not condense. The interior surface of the spray foam should roughly be the temperature of the occupied space. CC is an air and vapor barrier by itself. Summary: no poly is needed. |
