How thick should EPS foam insulation on basement walls be?
I'm researching about what type of rigid insulation to use when finishing my basement. I was on a website of an eps insulation manufacturer and under their technical/spec section for this particular rigid panel it says the vapour permeablility for 1" is 0.5 perms. would using 1" panel be sufficient instead of the recommended 2"?
EPS rigid foam insulation is made of tiny foam beads squished together, so there is a continuous path between the beads where moisture can move, but the rate moisture will permeate is reduced by increasing thickness.
I wouldn’t be in a position to speak to what performance statistics an individual manufacturer claims on their site, but the generally accepted permeability of foam is that at 2 inches it performs about like a Type II vapor barrier. Read more here about the characteristics and applications of different types of foam insulation, as they are all a bit different and not all great for the same purposes –
Choosing rigid foam insulation panels, which is best?
Do you have space limitations or budget limitations that is having you lean towards 1 inch? Since you will be going to the effort of adding rigid board insulation I would be doing more if you could. 2 or more inches would be better at preventing moisture movement, it will also save additional heat. Just food for thought since you’re going to the trouble anyway.
Thank you for your insight. Obviously I don't want to spend more money than necessary so if the 1 inch was sufficient that's what I would choose. But if minimum 2 inches is what's suggested then that's what I'll go with. Thanks again!
Happy to help Derrick. Worth considering is that if you are in a cold climate, then the added investment of going from 1 inch to 2 inches will pay for itself in a few years at most in heat savings, if not even in the first year. I'd do it anyway for the moisture though.