Should I Leave Space Between Thermal Barrier and Wall Insulation?
LESLIE: Rick in Pennsylvania, you’ve got The Money Pit. How can we help you today?
RICK: Well, yes, I have a question about a bedroom wall. I’ll tell you real quick what I have. It’s a cinder-block wall and on the outside of it is a stone facing. And then on the inside, they just had furring strips and then plaster. So, no insulation and very cold in the winter.
So what we’re doing – we’re tearing down the plaster. We’re going to frame it out. We’re going to put R-19 in there and they drywall it. But my question is – we were talking about putting a thermal barrier onto the block itself. And I guess I have a couple of questions or concerns: A) is it going to be worth it? Is it going to raise the R-value any? And B) there’s not really going to be an air cavity. It’s just going to be the thermal barrier on the wall and then the insulation is going to be touching that, so I’m kind of afraid it’s going to act more of a conductor.
TOM: Well, what you might want to think about using there is Tyvec.
RICK: Oh, on the inside.
TOM: Yeah, on the inside. It’s vapor-permeable, so I think it’ll allow everything to breathe but it’ll keep some separation between the block and the frame.
And by the way, you’d be wise to leave at least an inch there in between and not have it up against the block, because you really don’t want to have an organic material like wood – and certainly not drywall – that close to a very damp source, which would be the concrete block. Because concrete blocks are very hydroscopic. They suck up a lot of water and – especially in periods of bad weather. So you do want to have a bit of a space there. But I think that I would cover the block first with Tyvec, then I’d frame up against that.
Now, another option, to kind of kill two birds with one stone, is consider spray-foam insulation. If you did spray-foam insulation, you could frame the wall and then you could spray into the framing, right up against the block wall. And then it would be cut flush with the wall and you would put your drywall right on top of that.
Now, spray foam has the advantage of being able to not only insulate but seal and draft-proof at the same time. We recently added spray-foam insulation to our entire home. Now, we have an existing home, much like you. And of course, it makes it difficult to get into the walls. But what we did was we put it in the box beams, which were all the way around this sort of perimeter of the basement and crawlspace, and we added it to the attics. And just those areas – without even doing the walls, because we weren’t opening the walls at this time – made a huge difference in the energy efficiency of the house. So, I’m a big fan of Icynene – I-c-y-n-e-n-e – as a result of that experience.
RICK: OK. Yeah, I didn’t even think about anything like that. I have to check into that.
Do you know – well, I guess I have to let you head off the line or whatever – if there’s somebody around my area?
TOM: I’m sure that there will be. Icynene is a Canadian company but they have dealers all across the country.
RICK: Now, if I didn’t do that and I just put the frame – the stud – up to the block wall – you said to leave an inch. Like what would you recommend? How would you do that?
TOM: I would just simply frame the wall out away from the block.
TOM: And don’t attach the frame wall to the block wall. Because I’ll tell you, some of the worst cases of mold infestation we’ve seen is when you have wood framing attached to block walls and drywall which is, essentially, mold food.
In fact, one other thing you might want to consider is to not use drywall on that wall but use something called DensArmor, a fiberglass-faced drywall product. So without the paper face, you don’t have food to feed the mold. Make sense?
RICK: Alright. Well, thank you very much.