How thick should EPS foam insulation on basement walls be?

Derrick R
Updated: March 22, 2021

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"?

Responses (3)

Derrick R 3 years ago

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!

Emmanuel B. Cosgrove 3 years ago

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.