How to Insulate Without Causing a Moisture Problem

Find out how to insulate your home’s walls without causing a moisture problem. Get tips on putting a layer of foam over plaster and learn why your priority, before you even worry about wall insulation, should be attic insulation.

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LESLIE: David in Pennsylvania, you’ve got The Money Pit. How can we help you today?

DAVID: I have a question pertaining to moisture getting trapped in between the walls when you’re remodeling. On the outside of the house, there’s a ½-inch foam and I was going to put foam right over top of lath plaster and then put drywall over top of that. And I was wondering, am I creating a problem with moisture in the wall?

TOM: So, did you say that you have foam on the outside of your house? You have a faux stucco made out of foam?

DAVID: Somewhat like that. It’s like a Filatex (ph) product.

TOM: Well, there’s a type of stucco called EIFS – Exterior Insulated Foam Siding – and this is a problem – this is a product that’s associated with a lot of moisture problems and rot underneath and mold and things like that. I’d hate to see – to think that you’re adding to that, David.

DAVID: Alright. This is – it’s not like that but it – I am concerned that when you put a 4×8 sheet of ¾-inch foam or ½-inch foam on the outside and then do the same on the inside to try to create a better insulated value, if you are …

TOM: Why do you want to put it on the inside? Why would you not just use standard, fiberglass insulation in between the batts – in between the bays – in the stud bays of the wall?

DAVID: Well, it’s a plank house and it’s got real fancy trim and you can’t really do that.

TOM: OK. So you’re just looking to get an additional layer? And you want to put this on the wood structure or you want to put this over the plaster?

DAVID: Either way.

TOM: OK.

DAVID: If I can get away with putting it on the plaster, that’s the way I’d go.

TOM: You probably can. I don’t think you’re going to cause any additional moisture. The thing is, you’re making your walls awfully thick and you’re going to have to deal with that with the windows and the doors, because now your window wells and your door wells and your electrical boxes and switches – it’s going to be awfully thick if you do that. So you understand what that’s going to do? That’s going to pull everything – make everything deep, because the wall will essentially be an inch or two thicker.

DAVID: Right. I’m pulling all the trim off except for the baseboard and I’m putting jamb extensions on that.

TOM: OK. OK.

DAVID: I understand that, even with the electrical.

TOM: Yeah. And I will caution you, though, that the best place to save energy is not the walls; it’s the ceiling space above. So make sure that in your area of the country you have something in the area of 18 to 22 inches of insulation. Because the wall insulation is going to be much – you’ll save energy but the big heat loss is what’s going up.

And so, put it in perspective. Make sure you’ve got plenty of attic insulation first and then whatever you do to the walls will help after that.

DAVID: Alright. Thank you.

TOM: You’re welcome, David. Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.