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Polyethylene or peel-and-stick membrane?

haroto | Posted in Energy Efficiency and Durability on

I am working on a cathedral ceiling with exposed rafters. (Rafters, Tongue and groove, 5/8 plywood, 6″ of polyiso, 1/2 OSB, underlayment and metal roof).
I have available a 10 mil’ polyethylene roll that would cover the entire roof area in one piece. Is this an acceptable method for air sealing the system? I know this material doesn’t have the advantage of “self healing” around fasteners. Would that be a concern?
I am in Austin, Tx.

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  1. GBA Editor
    Martin Holladay | | #1

    Your roof assembly needs an air barrier. The air barrier can be the plywood sheathing (if it is properly taped), or a layer of peel-and-stick above the plywood, or the rigid foam layer (if the seams between the rigid foam are carefully taped, and if the rigid foam is installed in at least two layers, with staggered seams).

    Of all of these suggested air barriers, the peel-and-stick approach is best. I wouldn't use polyethylene if I were you -- because it isn't "self-healing," as you point out, and because it is slippery and dangerous for roofers installing the polyethylene.

    For more information on all of these issues, see How to Install Rigid Foam On Top of Roof Sheathing.

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