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I have a 2x4 framed garage with a previously insulated/vapor barriered ceiling. I added 2x2 framing to make 2x6 walls so I would have better insulation but have an issue connecting the wall vapor barrier to the ceiling. Since the ceiling joists run to the edge of 2x4 the new 2x2 framing does not have a matching top plate in the ceiling so there is not a consistent wood surface to attach and staple the wall/ ceiling vapor barrier together. Can I seal the vapor barrier to the existing ceiling vapor barrier with acoustical caulk and staple on the joists then drywall?

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That won't be a very reliable way of doing it, but you can. Acoustical caulk is used primary because it's gooey and soft, so it sticks well and doesn't create major humps in drywall. It sags over time, though, and may allow the two sheets to separate if they're not sandwiched between something rigid.

I suggest running sheet metal angle (like drywall corner bead without the bead) along the top of the new wall studs to create backing. Then seal the poly sheets together over the metal flange, and when you apply your wall sheathing it'll be pinched and secure.

Alternatively, such as if you're not installing wall sheathing, just get some good construction-grade tape to make the connection. Housewrap tape should do, I'd think.

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  • Thank you that’s a much better idea. In the end everything will get covered with drywall and all the seams tuck taped so that should hold. Originally I had originally tied in overtop the 2x2 framing in to the 2x4 vapor barrier from the ceiling but had moisture buildup in the winter in the gaps between the 2x2 top plate and the ceiling joists since it formed a gap. Hopefully this plus some foam insulation in the gaps will solve the problem so be I can move on to drywalling.
    – user153838
    Jul 8, 2022 at 1:12

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