Foil Face Fiberglass: Do Not Install with Existing Insulation
LESLIE: Mike in Iowa is on the line with an insulation question. What can we do for you today?
MIKE: I’m looking to put some fiberglass insulation up in my attic. I have access to some 6-inch that’s faced on one side and it has foil on the other. Could I lay that down in my attic without having any problems?
TOM: You already have existing insulation there, right, Mike?
MIKE: Yeah, I’ve got 10 inches in my ceilings.
TOM: The answer is no and here’s why: the foil face is a vapor barrier and if you put a vapor barrier in there, you’re going to trap moisture. Now, a very common scenario is people put that up in the attic, they leave the vapor barrier facing up but that’s actually wrong. The only place a vapor barrier belongs is against the heated space, which would be under the 10 inches of insulation you already have there.
So, the foil face is not a good thing. Now, I will say that you – if you really want to be frugal about this, you could probably pull that foil off and lay the unfaced batt perpendicular to what you have right now. It’ll be a bit of a messy job because it sounds like it’s older insulation, so you’re going to have to protect yourself with dust masks and safety glasses, long sleeves and all of that.
MIKE: I don’t care to do that. But right now, in my attic, at one time I had a flat roof. And right now, I’ve got rolled tar – or not tar paper but rolled shingling up in my attic floor. That’s probably acting as a vapor barrier, I would guess, today.
TOM: It probably is, yeah. Because it would stop humidity from getting through it. The problem is that it traps it in the insulation and when it does that, the insulation doesn’t work well. Insulation that’s damp does not insulate, so that humidity is working against you.
MIKE: I have wood heat and it takes a lot of moisture out of the house. That’s probably in my favor, I would guess.
TOM: I would think so. Now, you want to preserve that wood floor? You want to use all of that wood floor space?
MIKE: I’d like to use as much as possible, yes.
TOM: Well, why don’t you do this? Kind of a way to kind of have your cake and eat it, too, is to carve out an area in the center of the attic that you reserve, basically, just for storage. And then you add unfaced fiberglass batts on top of the wood floor to the other areas. Yeah, it’s not perfect having that whatever floor covering you have in between but I still think it’s going to add some insulation to that space and help cut some of your energy bills. And unfaced fiberglass batts are not that expensive and pretty easy to handle.
TOM: Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.