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air barrier needed behind T&G vaulted ceiling?

caseyspradlin | Posted in General Questions on

New Construction in central Alabama.

I have a living room with vaulted ceiling that has attic space between vaulted ceiling joists and roof rafters.  I also have a vaulted bedroom ceiling in which the vaulted ceiling joints are the roof rafters.

I am open cell foaming the roof and walls.  I had originally planned to just attach T&G pine directly to the ceiling joists in both locations.  But now I see that some are air sealing between ceiling joints and T&G.  

What is advantages of this?
What is cheapest way to do this?  Is Tyvek with tapes seams an option?

Thanks very much for the education.

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  1. Expert Member
    BILL WICHERS | | #1

    Assuming your spray foam is thick enough, and it probably is if you’re filling rafter cavities, the spray foam alone is an air barrier and should be sufficient. Open cell is typically overfilled and then trimmed flush with the edges of the framing, leaving no voids. If there is going to be a kid behind the T and G (such as would usually be the case with a closed cell spray foam installation), then you’d probably still want an air barrier.

    Drywall is typically used as an air barrier here. I’ve used 1/2” polyiso too. I suppose housewrap could be made to work too, but it’s much easier to damage and I’ve never used it for this application myself.


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