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How to Seal Air Leaks Above Wall Plates in Attics

This video is only available to GBA prime members

Conditioned air moving through light switches and other wall penetrations can find its way into the attic, too. Seal where the drywall meets the top plates to solve this problem.

Thermal Bypass Checklist package (50+ details).

Get your finger ready—and some caulk, spray foam, or acoustical sealant

Video Transcript:

Where the wall plates of interior partition walls come up to the bottom of the ceiling joist, we’ve got gaps between the drywall and the plates themselves, and those plates are going to run either perpendicular or parallel to the ceiling joists. Where we have it perpendicular, the wall plate you can see in the drywall. And over here, where we have it parallel, they put in 2×6 blocking that supports the ceiling drywall but sits on top of that top plate.

There are slightly different approaches to sealing both of those situations. Between the drywall and the top plate of the wall, we’ve got a few different choices of materials we can use to seal up. Probably the simplest and easiest is just a really good, high-quality caulking. You want something that’s elastomeric, which means that it’s stretchy after it seals up. I tend to go for something that’s a little less expensive but works just as well, which is an acoustical sealant. It usually comes in larger tubes, and you find it at commercial suppliers. The stuff is very sticky, and it doesn’t completely cure—and that’s important. It’ll skin over, but it’ll stay sticky, stay adhesive, and be able to move with the materials as moisture, temperature, and so on change the dynamics of the material.

Now, another choice would be a high-expansion or low-expansion spray foam. One of the challenges with this stuff is that it’s only good when…

One Comment

  1. mike keesee | | #1

    good stuff. We need more of
    good stuff. We need more of this. I've seen the problems associated w/ the spray foam in the field - I can show you pictures. Curious to know what expereience people have had w/ the owens corning energy complete system and the knauf eco seal system. What's really needed is something like the eco seal system but that's available as a sealant and not part of an insulation package.

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