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Air Sealing Before (and After) Hanging Drywall

Sealing big and little holes in walls, floors, and ceilings with caulks, sealants, and spray foams
January 15, 2024
Read time: 3 mins

This is a new house that I'm going to be drywalling soon. I'm just going to do a walk-through here and point out what I'm going to be air sealing.

Seal behind the electrical boxes and holes for wires

See this electrical box and the outside of this wall? We're going to be putting foam behind that to make a good air seal. This house is 2x4 construction because it has a bunch of foam on the outside, so that's why there's just a small gap behind here. Fiberglass insulation won't do anything tucked in behind it, so, we're putting foam behind the electrical box.

See this hole going through this wall right here? That's going to be air-sealed with foam. I usually air seal any hole that goes down in the basement, like this wire that goes down in the basement, and then it goes up here and then eventually up into the attic. That's all going to be foamed.

I usually foam the bottom of this plate right along the bottom edge here and then along the top here, too, just to seal that in. You know, gaps like where this header goes out, that's what I will be air sealing. 

Air seal the ceiling from the attic after hanging drywall

Once the drywall is hung, we go up into the attic, and we spray foam around every one of these light boxes along the ceiling. So, there's going to be quite a bit of work up in the attic after it's drywalled because they're blowing in cellulose here. So, the first thing that's going to happen is the ceilings are going to be hung, then we go up and air-seal all that with foam, then the cellulose will be blown in.

There are a lot of windows in this house. All these gaps have to be air-sealed with low-expanding foam. A couple of exterior doors also need that, so we definitely have to use a variety of foam products.

See this area up here, where we've got the prop-a-vents? How he's got it blocked off with a form along the back, and then he's got the prop-a-vent going up. See that gap where you can see daylight coming in? That has to be sealed with a spray foam so that the cellulose doesn't go down in that area.

Basement air sealing opportunities

I'm going to go down to the basement and see about the rim joists. I don't think they've done anything with them. Yep, nothing's been done. You can see it's just plain wood right now. So, all that is going to have to be sealed in really well. I usually spray foam these cavities with 2-inchs of closed-cell foam froth packs.

We also look for anything in the ceiling in this basement, like, a lot of times I look for the shower, which I don't know where it is in here, but a lot of times there's a big hole going right up into the shower. I don't think the plumbing is done yet, so here's a hole for the toilet, and I know where the shower is. So a lot of these areas in the basement get foamed, and they should all be foamed with a fire-resistant foam.

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