The Right Way to Put Up Insulation
LESLIE: Alex in D.C.’s up next with an insulation question. What can we do for you?
ALEX: Well, the previous owner put insulation in the attic and the crawl space under the house. But I’ve – I heard, during my home inspection, that he did it backwards. Basically, in the attic, the paper vapor barrier is up.
TOM: Oh, that’s bad.
ALEX: But also, the inspector said it looks like someone tried to make a minor repair. They cut a bunch of slits in the paper.
TOM: Actually, that’s the exact right thing to do, Alex.
TOM: Yeah, so that’s not a – that is a repair and that’s the perfect thing to do because that vents the insulation.
ALEX: The purpose, I guess, of the vapor barrier is to keep the moisture either out of the house or in the house; I’m not sure.
TOM: It’s supposed to keep the moisture on the conditioned sided of the house and not let the moisture wick up into the insulation. Because once it gets into the insulation, the insulation becomes ineffective. If you take insulation – say, six inches of fiberglass insulation has a value of r19 – and you add two percent moisture to that, it reduces its effectiveness by a third. So keeping insulation dry is important. If your vapor barrier’s backwards – and usually I hear about this in the crawl space when people are installing insulation and they use the paper lip; they like staple it to the underside of the beams …
ALEX: Yeah, they did that, too.
TOM: Yeah well, generally, there, I tell – I tell folks to take a utility knife and cut it about every six to 12 inches so that it’s thoroughly vented. In the attic, I am more concerned because there’s a lot of vapor pressure that pushes up there and even if you have that slit, there’s still a decent chance you’re going to get moisture in there. So, in areas where the insulation is easy to access, I might recommend taking that out and putting unfaced fiberglass insulation there in its place.
ALEX: Great. Well I appreciate your help.
TOM: You’re welcome, Alex. Thanks so much for calling us at 888-MONEY-PIT.