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How to Air-Seal Soffits and Chases in an Attic

Thermal Bypass Checklist package (50+ details).


We’re up in an attic; downstairs, there’s a kitchen with a soffit above all of the upper cabinets. When we came up here, we were on the lookout for one of the biggest holes you find in an attic, which is the area above the soffit. Drywall usually doesn’t get applied to the ceiling before the soffits are framed in, and it ends up being a big leaky hole. This one was easy to find because I could already see the insulation drooping between the ceiling joists. When I pull the insulation out, I uncover the cavity of the soffit below. In the cavity there is a recess light can (which isn’t air sealed), a ceiling or junction box, and there’s also a gap around the bottom of this plumbing pipe. In the back there are holes that are going down and into the wall cavity between the studs and the adjacent wall. There are a lot of places where air is leaking up into the soffit. That is certainly evident by the insulation. If you look closely at the insulation, you can see a lot of fine dust that has collected along the sides as the air has leaked through over time. This is one of the biggest air leaks, therefore it’s one we want to ignore. The easiest way to deal with this is to use some sort of rigid panel. There are a couple of choices. One would be a piece of rigid insulation, which is what I prefer because it gives you insulation value as well as it’s lightweight and easy to handle. Another alternative is scrap drywall, or even scrap plywood or OSB. Fit whatever rigid panel you choose into the cavity, caulk around the perimeter, and you’re done.…


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