Insulation Installed Incorrectly May Cause Moisture Problems

LESLIE: Paul in Indiana needs some help with insulation. What can we do for you?

PAUL: Oh, I’ve got an older, ranch-style house and it had no insulation in the walls, so I needed to put siding on. I ripped the old siding off and the black Celotex and put insulation in and then put the OSB back on it and my siding. I’m about half done but where I put the insulation in, I turned it on backwards.

TOM: (overlapping voices) OK. Oh, so you have the vapor barrier on the outside of the house.

PAUL: Yes.

TOM: (chuckling) Ruh-roh.

PAUL: Not much I can do about it now but I thought about it and I know what that’s for and all that but I thought it’d be better that way than no insulation.

TOM: And I bet you did a really good job attaching that vapor barrier; you made it nice and smooth and tight so that there were no gaps or cracks, right?

PAUL: Yeah, I did. (Tom laughs)

TOM: Hey, if you’re going to go – if you’re going to do it, you might as well do it right, even if it’s wrong.

PAUL: Yeah. That’s what I thought, maybe.

TOM: Well, did you put anything else over it? Did you put any – did you put Tyvek or anything of that nature?

PAUL: Oh, yeah. I put house wrap on top of the OSB.

TOM: (overlapping voices) House wrap on it? Hmm. Well, you know, it may not be terrible. What’s going to happen here is your insulation is going to be damper than it should be, which means it’s not going to insulate as well as it could. But if you have a relatively dry house, then I don’t think it’s going to cause any type of long-term problem; it’s just going to basically result in inefficiency of the insulation.

Because what happens is, insulation is measured in r-factor – r-value. And when you add two percent moisture to insulation, the r-value goes down by a third. So, for example, if you add six inches of insulation, which is r-19, you add some moisture to it, it’s kind of down to r-12 really quick. So the insulation will probably be not as effective had it been – that it would have been if you had done it correct from the get-go. But I don’t think that it’s going to be so bad that you’re going to have moisture buildup inside the walls and rot and that sort of thing.