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Tyvek window detail not air tight?

quantumgirl | Posted in General Questions on

I can’t wrap my head around the Tyvek window detail. I think it allows air to enter the building or maybe I’m just overthinking this.

Regular 2×4 stud wall with ply sheathing. Sheathing seams and window rough openings are taped. Next, Tyvek is installed according to their instructions: cut at windows and wrapped around the jambs, stapled to the inside of the jamb stud. Sill is flashed with Flex wrap. Then the nailing fin windows are installed and flashed.

Im using the Tyvek as my water barrier, not my air barrier (bottom is not taped). My air barrier is the taped sheathing along with spray foam insulation.
So since air can get behind the Tyvek, from there, wouldn’t it be able to move to the inside of the building as indicated on my sketch? Am I missing something? 
Should I have followed the alternate Tyvek installation method where windows are placed before the Tyvek?

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    quantumgirl,

    Yes you are right. The house-wrap is best terminated at or very close to the exterior of the window opening. One way of doing the is to install the windows before the Tyvek: https://www.youtube.com/watch?v=SqP4liutJFs

    1. quantumgirl | | #2

      Thanks Malcolm. That’s what I thought. Do you see any way of fixing this if I already have my windows and siding in place? I assume trying to get my interior drywall as air tight as possible with caulk and gaskets would be my best bet now?

      1. Expert Member
        Malcolm Taylor | | #3

        You should be able to cut back the house-wrap flush with the inside of the window frame, and can probably push it further back into the gap with a small flat-bar. As long as you can get 1/2" or so of framing exposed you can seal with foam or caulking.

        A small amount of air can also make its way in-between the sheathing and framing at the opening. You can reduce that by caulking on the other side of the studs surrounding the window, although I'm not sure it's worth bothering about.

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