Adding a Vapor Barrier to Walls and Ceilings
LESLIE: Michael in Arkansas, you’ve got The Money Pit. What can we help you with today?
MICHAEL: Hi. I’m building an addition on my house and I was wondering about a vapor barrier between the sheet rock and the walls and the sheet rock and the ceiling.
MICHAEL: And I’ve had other people tell me, “You know, well, on the ceiling, it draws moisture and it’ll ruin your rock,” and other people tell me not and so I thought I’d just ask the experts.
TOM: OK. Well, the vapor barrier goes between the heated and the unheated space. So, in the case of the ceiling, it basically would go up against the rafters, before the drywall. And that’s why insulation – batt insulation – has a vapor-barrier face to it. And it has those nailing flanges so that, basically, it attaches to the ceiling joist and that, in fact, becomes the vapor barrier. Now, do …
MICHAEL: So I wouldn’t need one. I wouldn’t need a …
TOM: You would not need to use plastic, no.
MICHAEL: You wouldn’t need plastic up there?
TOM: The back of the vapor barrier is essentially attached to the insulation already.
MICHAEL: OK. So if it’s up – if I’m using blown insulation …
TOM: Well, if you’re using blown insulation, then you could use a vapor barrier.
TOM: I don’t see any reason not to.
MICHAEL: So then …
TOM: But again, it goes between heated and unheated. So, it would basically go right under the drywall.
MICHAEL: OK. So if I’m just using batts, though, I don’t have to – I don’t really need – it wouldn’t do any good.
TOM: Correct. No, no. And listen, it’s going to help a little bit but the key to keeping your insulation dry is to make sure you have the right amount of ventilation. So you need to have plenty of ventilation in the attic space. I personally like ridge vents and soffit vents, because they work together to flush air out of the attic 24/7. They’re even more effective than attic fans.
MICHAEL: OK. Alright. Well, thank you for your time.
TOM: You’re welcome. Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.