Do I Need More Attic Insulation?
LESLIE: Bud in Illinois, you’ve got The Money Pit. How can we help you today?
BUD: I’ve got – this house is built probably in ’38 – something like that – and it has a floored attic but with blown-in insulation. I think they’re about 2x6s or 2x8s. But the problem is I’d like to know if I need more insulation up there. And I have one window – a regular-size window – in the gable end.
BUD: And over the last 48 years, I have closed that thing up entirely in the winter and then put a screen over it, because of an exhaust fan.
TOM: And your winter just wouldn’t be right if you didn’t close up that vent, Bud.
BUD: Well, it gets kind of cold, yeah. Well, what I had was a builder told me to put a louvered window in there, so that the fan can take care of the heat.
TOM: OK. Because of the ventilation issue. Right.
BUD: And to leave it open.
BUD: So I’m just wondering what I should – should I go ahead and close it up completely in the winter?
TOM: Alright. So the attic is an unfinished attic. You use it for storage, correct?
BUD: Right, right.
TOM: You have – you think you might have 2×8 ceiling joists and they’re insulated but the flooring is above that, correct?
TOM: So, you do not have enough insulation based on current standards. Current standards would be 19 to 22 inches. Are there spaces in that attic floor that you’re not using for storage?
BUD: No, no.
BUD: It’s a little Cape Cod house; it’s got a small attic.
TOM: Alright. Well, then, you’re pretty much going to be giving up the opportunity to put additional insulation in there, because you’re using every square inch for storage. I was going to tell you, if you didn’t have storage all over the place, you could lay unfaced fiberglass batts on top of the floor and have them do the job.
BUD: Oh, OK.
TOM: But if you have that kind of a storage that sort …
BUD: Well, maybe I could move everything to one end.
TOM: Yeah, well that’s what – generally, what we do recommend is that you carve out a space for storage.
LESLIE: Like one, specific storage area.
TOM: Right. And the rest of it, you can lay fiberglass batts on top of the flooring and see if you can …
BUD: OK. And what thickness on that?
TOM: Well, 19 to 22 inches total. So if you’ve got 8 now, I would try to use at least 10 or 12-inch-thick batts and lay them right down, end to end, right on top of the existing floor.
BUD: Just lay them down?
TOM: Lay them down.
Now, in terms of your friend/builder advice, the guy is actually correct, because attics are supposed to be ambient temperature; they’re supposed to be the same temperature as the outside. We don’t insulate them; we try to let a lot of fresh air blow through them. And in doing so, they cart away moisture in the wintertime, which can affect the insulation. Because if your insulation just gets slightly damp, it becomes very ineffective. In fact, if you add 2 percent moisture to insulation, it reduces its effectiveness by about a third.
BUD: So what am I going to do, though, if it blows in rain and that sort of thing on top of the insulation?
TOM: Well, if your vent is designed as such where if you don’t cover it, it’s going to get wet, then that’s a problem; then you do need to cover it. But you just need to make sure you have enough ventilation.
BUD: I do have roof vents.
TOM: OK. And do you have any evidence of condensation on the underside of the roof sheathing? Do you ever see rusty nail tips or anything like that?
BUD: None. No.
TOM: Well, if you’re not getting any condensation, then you might just have enough ventilation with the way it’s configured right now. But the guy is technically correct, because you don’t want to close-in vents.
BUD: Well, we’ll go from there.
TOM: Alright. Good luck with that project. Bud, thanks so much for calling us at 888-MONEY-PIT.