Find out whether air sealing or insulation delivers the better return on investment. Learn why you should first prioritize cutting down drafts, then focus on attic insulation before wall insulation.
LESLIE: Well, when it comes to making your home energy-efficient, there are certainly lots of choices and it helps to set some priorities so that you can pick a place to begin.
TOM: That’s right. And the two most common moves to make homes more efficient are to increase insulation and to decrease the amount of air that can leak in and out of a house. But even with those, which delivers the best return on investment? Well, let’s find out as we welcome This Old House  general contractor, Tom Silva .
TOM SILVA: Well, thank you. It’s nice to be here.
TOM: Now, you must be faced with questions like this every time you start to tear open one of those grand, old homes that you guys make over. Homeowners want to know how they’re going to get the best energy efficiency out of their renovation. Where do you begin on that air sealing versus insulation question?
TOM SILVA: Well, the air-sealing part comes in real early here, because there’s a new code out there that actually requires that I have an inspection – another form of inspection – for the inspector to come out and make sure that I do certain things.
TOM: OK. Oh, that’s interesting. So, when we think about the building inspector looking at the foundation and the framing and the mechanicals and making sure the roof’s there, now they’re really looking at this important energy question, as well.
TOM SILVA: That’s right. The energy is – is they have to come out before I insulate.
TOM SILVA: And they want to make sure that before the siding goes on that the windows are sealed up correctly on the outside.
TOM: So all those drafts are now covered by code-enforced inspections.
TOM SILVA: Absolutely. Any of the joints in the plywood.
LESLIE: Now, is this something that really only applies to a new construction or is this when you’re adding an addition or working on a major renovation? Do you have to sort of take this step with the res code, as well?
TOM SILVA: You have to take this step with the res code. It follows a little bit different when you’re doing a renovation and addition. The old part is more forgiving than the new part. So, if I’m doing an addition, for example, I have – that addition has to meet the res check but the alteration has to be insulated but it doesn’t have to be opened up to be insulated. So you can assume that it’s insulated and you can – any wall. If I just opened up one part of a wall, I’d have to insulate that section. I don’t have to do the whole wall.
TOM: So air sealing  really is a priority, then, over insulation today. Let’s say we get the air sealing correct and we’re doing everything we’re supposed to be doing. Now we want to look at the insulation. Is there a priority, in your mind, between, say, floor insulation, wall insulation and ceiling insulation, as to what the most important place of your house is to insulate?
TOM SILVA: Well, once you’ve cut down the drafts, now you have to think about heat. Heat rises. So, what do you want to do? You want to put the hat on the building; use the warmest hat to keep it warm. The next thing you’ve got to think about, the walls. You want to tighten those up.
I like to insulate levels. So if I live in a two-story building, I like to insulate the first floor and the second floor. I want the heat that’s in the first floor to stay in the first floor. I want the heat in the second floor to heat the second floor.
LESLIE: Now, if you’re insulating between the first and the second floor, because you’ve got two conditioned spaces, in essence, do you use unfaced batting or is it better to go with, you know, more of a foam type?
TOM SILVA: You don’t need a vapor barrier at all, in a space that’s heated above or below.
TOM SILVA: So, it’s unconditioned space needs a vapor barrier and you’ve got to think about what part of the country you live in and where do you want that vapor barrier. For example, if I live in Florida, I want the vapor barrier to be on the outside of the building. If I live in New England, I want the vapor barrier to be on the inside of the building, because I heat more than I cool.
So, condensation can form on that wall surface in New England, for example, and it’s going to get to the outside of the building, it’s going to collect on the back side of the sheathing, frost is going to build up inside that wall, it’s going to run down and my sills are going to rot, my paint’s going to peel.
TOM: And that’s really critical, because that condensation – I mean we think of insulation and we measure it by R-value but if you add 2-percent moisture to insulation, you reduce the R-value by up to a third. So it’s very, very important that you have insulation be as dry as it possibly can be.
TOM SILVA: Absolutely. The moisture is the enemy, whether it’s coming from the inside or the outside. And you want to keep that building tight; you want to make sure your vapor barriers are on correct. You want to make sure all of your electrical boxes are sealed up nice and tight. There’s all kinds of new things out there that you have to be careful of.
TOM: Well, there’s an awful lot of new tricks that the old contractors out there – you excluded, my friend – are learning about how to make homes more energy-efficient and I tell you, it’s really, really great for everybody. It’s saving money; it’s making those homes so much more comfortable, as well.
TOM SILVA: Absolutely.
TOM: Tom Silva from TV’s This Old House, thanks so much for stopping by The Money Pit.
TOM SILVA: As always, it’s my pleasure.
TOM: To learn more about air sealing and insulation, you can visit ThisOldHouse.com.
LESLIE: And make sure you watch Tommy and the entire This Old House team on This Old House and Ask This Old House, on your local PBS station.
TOM: And This Old House is brought to you by State Farm Insurance. Like a good neighbor, State Farm is there.