How to Install the Right Amount of Insulation

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    LESLIE: Well, no matter where you live, it’s hard to stay comfortable and keep your energy bills in check if you don’t have enough insulation in your attic. The truth is that most of us just don’t and adding more is almost always a cost-effective project.

    TOM: Yes. But as simple as it might seem to add insulation, it’s a project that many do-it-yourselfers just get wrong. With us to make sure that doesn’t happen to you is Kevin O’Connor, the host of TV’s This Old House.

    Welcome, Kevin.

    Tips for Installing InsulationKEVIN: Hi, guys.

    TOM: Now, insulation is one of those building components that’s always out of sight and out of mind. That is, of course, until you open your very first energy bill of the season. How much insulation do we need?

    KEVIN: Well, that’s a really good question and I think it is a great project for folks to do themselves but, as you say, they need to get it right. And how much you need is the first question. That depends on where you live.

    So in the warmer-weather states, you’re looking for something that’s like an R-38. And in the colder climates, that goes all the way up to an R-49. Now, these are metrics that come to us from ENERGY STAR. And that means – I mean think about this: R-38 to 49, that’s about 10 to 16 inches of fiberglass insulation batts.

    TOM: That’s a lot of insulation and I think most folks, just taking a look up in their attic, are just not going to see that.

    KEVIN: Well, they’re going to see that they might have insulation but the rule of thumb is, more insulation is generally better, so add it on.

    LESLIE: Now, Kevin, increasing the amount of insulation you have in the attic really is a very, very helpful project that you could have in your home. But is it a do-it-yourself project?

    KEVIN: Oh, it definitely is a do-it-yourself project, whether you’re increasing the amount of insulation or you’re just adding insulation for the first time. Imagine when you’re working up in the attic, if you don’t have anything in those bays between the ceiling joists, well, these batts are designed to lay right down into those bays, 16 inches on center. So you can fill in those bays and add insulation.

    If it’s already there, it’s a great idea to increase the amount of insulation. The only tip that I would say is that you want to lay the second layer of insulation perpendicular to the first and to those ceiling joists so that you cover up any of those gaps.

    LESLIE: And you want unfaced-batt insulation, correct?

    KEVIN: You do. Because that facing is actually a vapor retarder and you don’t want that in the wrong spot. So you want to make sure that you use unfaced insulation. Lay it across, cover up all those gaps and cracks and pile it up.

    TOM: Now, another thing to watch out for are the light fixtures, especially those high-hat sort of ceiling can lights that protrude up into the attic. If you don’t have the right kind and you cover them with insulation, it could cause an overheating situation.

    KEVIN: It can. And so there are basically two different kinds: those that are rated to be in contact with insulation and those that are not. You need to make sure that the cans or these recessed lights that you have up there are rated to be in contact. If you don’t know, err on the side of caution and don’t cover them up with insulation.

    TOM: Now, Kevin, besides putting a lot of insulation in an attic, we also have to have enough attic ventilation so we don’t make the attic either too hot or too moist in the wintertime or too hot in the summertime. So I think it’s important to be very cautious, despite the fact that you want a lot of insulation, to not block your ventilation, correct?

    KEVIN: Right. A lot of these attics are designed to be vented, as you say. And that means the air will come in through the soffit through a soffit vent, go up through the rafters and then out either a gable vent or a ridge vent. And if you block those, your roof’s not going to – your attic’s not going to perform like it should. So they have cardboard baffles that you can use and you actually put the baffles in there to make sure that the insulation doesn’t cut down on any of that venting.

    LESLIE: Mm-hmm. Now, what if you have any sort of open areas or cracks where you might get some air leakage between your living spaces and your attic? How should you fill the …?

    KEVIN: Well, you want to fill all of the cracks as much as possible. You can do it using caulk or you can actually use expanding-foam insulation. You’ve seen these cans at the home center; you can actually use those to fill in those gaps and cracks. Because it’s not just about the R-value but it’s also about the movement of air. So air sealing is a great way to go.

    TOM: So this could be the areas where pipes come through the walls or wires come through the walls. All those little holes add up.

    KEVIN: They sure do add up.

    TOM: Now, what about the difference between blown-in and batt insulation? It seems that blown-in insulation is great because it absolutely covers everything and you don’t have to worry about positioning it as much. But because it covers everything, you can’t get to anything once you’ve installed it.

    KEVIN: Yeah. Blown-in insulation is great, as you say, because it covers all those nooks and crannies. But imagine if you have to go back to that place to do some work: you either have to fix a light or you want to run some new wires. Well, it’s not easy just to peel out of the way like a fiberglass batt.

    So if you think you’re going to need access to that space, fiberglass batts may be the way to go. And in terms of storage, if you want to use that space for storage, well, maybe you carve out a little area for storage and don’t insulate it with the blown-in but blow in around that area.

    TOM: Good advice. Kevin O’ Connor, the host of TV’s This Old House, thanks so much for stopping by The Money Pit.

    KEVIN: Thank you for having me.

    LESLIE: Alright. You can catch the current season of This Old House and Ask This Old House on PBS. For local listings and some great articles on how you can improve the energy efficiency of your house and the insulation, as well, visit

    TOM: And This Old House and Ask This Old House are brought to you by The Home Depot. More saving, more doing.

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