How To Install Fiberglass Insulation | This Old House

I'm going to take this first bat here and I'm going to go to this nice open bay right here and I make sure you start here at the top and then make sure the top is really pushed up nice and tight and even and when you're installing it when you're coming down don't push it in too much or you're going to compress the R value and we don't want to do that. You like it nice and fluffy. Yep and then you're going to bring it down here to the bottom plate here and we're going to cut it along the bottom plate right here just a little bit longer. than it needs to be so we get a nice good friction tight fit. So no tape measure, just cutting it in place? No, I'm cutting it all by eye and I'll move on to the next bay here. Alright, here's the second one. Thank you. Looks like you've got a system where you lay it out just in the right spot and move your way down. Now in this bay we've got our first obstruction. We've got ourselves an electrical box. Yeah. How are you going to handle that? Right here, you don't want to just cut the outlet out. You want to make sure you get against here and you pull the bat and split it. Make sure you tuck behind the outlet. And get in there nice and tight so we have no cold drafts coming in. Then you slice the bat above the electrical box here and then below here. Take this little piece here, curl it in nice and tight. So we've got a full width bay but we've got two air conditioning lines running right down the middle. How are you going to handle this? Well we used to take the insulation and just tuck it behind here. The whole bat. The whole bat. But we can't do that anymore because it compresses the R value and you won't get the proper effectiveness of it. So we take it and we split the bat here in the middle like this. And pull it down the entire length. Down the whole length, making sure you get it nice and even so you get both parts. Yep, two thinner bats. Yep, you take this piece here, pull the pipe out, tuck it behind here, pull it up nice and tight, making sure there's no voids or gaps, and tuck it the whole length of the bay all the way down to the bottom here. Pulling it nice and snug, make sure it's in there nice and good. Take the other piece here. I love it. Just lay it on top? Yep. All right, so we've got the same obstruction in this bay and then we can just work our way right around the room. It's real important that we insulate and air seal around all the windows with low expansion foam made for doors and windows. So you've got the professional's version here. You've got this fancy applicator tip. Or you can get a consumer version with the plastic applicator tip. But we want to make sure whatever one we get that it's low expansion foam because you've got a chance of bowing the windows. Some foam expands too much. Yes, and you don't want to bow the windows or you won't be able to open them correctly. But they will be sealed. Yes, they will. You want to start at the top and go slow. Work your way down and make sure you're filling the whole cavity with foam. Okay, we took care of the walls, we took care of the windows, now we need to take care of the area above the walls. Up here, they're called blockers. I've already cut some, pre-cut to fit between the joists. Just going to stick them up in here, tuck them up nice and tight, make sure there's no void. Alright, that is the last one. So Dave, let me ask you a question. Up top on these blockers, we are using fiberglass bats with a paper face and this is the vapor barrier, right? Yes it is, yep. And we like vapor barriers because, well, in this climate, in the winter, we've got warm, moist air and it's trying to get out of the house and we don't want it condensing on the fiberglass, making it wet, so the vapor barrier helps prevent that. Exactly. Why have you got a vapor barrier up there but no vapor barrier down here? Well, ideally I like to cover The whole wall with a continuous vapor barrier. Pull the poly tight all the way down to the bottom here. All right, let's staple the bottom here. All right, now Dave, what about our windows though? We've got them completely covered here. Yeah, we're gonna cover those. We're gonna leave this up until they're done doing the drywall. They'll protect the windows. Okay, looks pretty good, right? Yeah. And we got a little bit of everything, right? For insulation, we got fiberglass and foam. And for vapor barrier, we've got paper and three mil poly. And that's how you insulate a wall.