Types of Insulation

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  • Transcript

    LESLIE: Well, if your winter heating bill is sending a chill down your spine, you are not alone. Millions of Americans are feeling the chill in their wallets and in their homes.

    TOM: Well, part of the cure is more insulation in your attic. But insulation comes in many different types, so how do you know what to use? Here to give us an overview of the options is This Old House general contractor Tom Silva.

    Welcome, Tommy.

    TOM SILVA: Well, thank you. It’s nice to be here.

    TOM: Every day we’re seeing more and more types of insulation hit the market. How do we compare insulation, in terms of performance, to really make the best decision for our homes?

    TOM SILVA: Well, you’re right. There are a lot more of insulations out there now than there ever were and it’s really the – you think of the insulation as the R-value or the thermal resistance to the heat flow that is either leaving your house or coming into your house.

    TOM: And that R-value is how it’s measured, right?

    TOM SILVA: Exactly. Per inch and it’s usually like an R-13, it would be, for a 2×4 wall; R-38 could be for an attic. And you want to make sure that you have the right value for the area of the country that you live in, because the codes require different grades of insulation or different R-values.

    TOM: So, if you’re in Minnesota, you’re going to have a lot more insulation in your attic, for example, than say if you’re in New Jersey where I am?

    TOM SILVA: Exactly. Well, for example, in New England, where we are, the building code says R-38. But as of this year, I think they’re going to change it to R-40. And the walls are R-20 or R-21. So, oh, the old R-13 in a 2×4 wall won’t pass building code.

    TOM: I think what surprises a lot of Americans is when they actually do look into what the recommended R-values are for their particular area – is they just don’t have enough.

    TOM SILVA: They don’t have enough. No, I think more houses don’t have enough insulation than do, that’s for sure.

    LESLIE: So, Tommy, with so many different kinds of insulations available – you’ve got spray foam insulation, you’ve got cellulose insulation, you’ve got fiberglass – to achieve R-value, is it the same across the board? Does that number sort of work out all the same, based on the type?

    TOM SILVA: Well, yeah, it does work out the same but for different types of insulation, it requires different amounts of insulation in that cavity.

    TOM: So some insulations have a higher R-value per inch than others?

    TOM SILVA: Exactly. Point in place, let’s say closed-cell foam as opposed to open-cell foam. Open cell foam is 3.6. Closed cell foam is 6.4.

    LESLIE: Per inch.

    TOM SILVA: Per inch, which makes a big difference.

    TOM: Now, also, what plays into this is the ability of the insulation to also seal out all those drafts that are getting in. I guess foam or dense pack might be a better candidate than, say, batt insulation.

    TOM SILVA: Right. It’s air sealing. And air sealing is basically where you feel a draft from cold air blowing through or the warm air getting out. It can cause problems. But air sealing is key.

    TOM: So important to consider both the R-value and the air-sealing capability of the product you’re choosing.

    TOM SILVA: Absolutely.

    TOM: Alright. Let’s talk about a couple of installation tricks to address some of the things that I commonly see wrong. Say we have fiberglass insulation in the attic right now. Perhaps it’s level with the floor joists, maybe you have 8 or 10 inches. You want to add a second layer. Faced or unfaced?

    TOM SILVA: Absolutely unfaced. The face on the insulation – the paper face, craft face, foil face – is basically a vapor retarder. And that vapor retarder will stop the air that’s swollen with moisture in it when it comes – it may want to go through the insulation but that retarder will block the moisture from getting into that insulation. Some may get in there. If you go over the insulation that you have with more paper face – you create a paper face between insulations …

    LESLIE: Now you’re trapping that moisture.

    TOM SILVA: Now, you’re going to trap it between the two and the bottom layer of insulation will get wet.

    LESLIE: Now, what if your base layer of insulation in your attic is all crushed and kind of, you know, worse for the wear? Better to just go over that or get rid of it and start over?

    TOM SILVA: I like to take it out. Some people don’t want to deal with it. You can go over it but again, you want to go over it with unfaced insulation – fiberglass, mineral wool – or you can blow in cellulose or blow in fiberglass. More is better. If you have the room, you don’t use the attic for anything, just pack it right up there.

    TOM: And of course, the one additional point that so many people forget is that when you add extra insulation, you also need to have adequate ventilation for that to work right.

    TOM SILVA: Yeah, you want to make sure that you have a negative pressure to be able to pull the air out up high. But you also are going to make sure that you have to have a positive pressure so that the negative pressure can work. So it’s like a bottle that has a hole in the – you try to suck on that bottle, you can’t unless you put a hole in the bottom of it.

    TOM: So the practical way to accomplish that might be with soffit vents that let the air in and then ridge vents at the peak to let the air out.

    TOM SILVA: Exactly. Yep. Ridge vents or gable vents or even a mushroom vent. Anything up high, because that’s where the heat rises, and it’ll pull out.

    TOM: Tom Silva, the general contractor from TV’s This Old House, thank you so much for warming us up with great insulation advice.

    TOM SILVA: Always my pleasure.

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