GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

EPS Type 2 Perm Rating

grantharvey | Posted in General Questions on

Posted this under a “musings” post, but it was an old one and thought I might get more traction here.

For basement walls; how thick is thick enough for EPS to act as a vapor barrier? I’m in the process of insulating my poured foundation walls. I had immediate access to some free left over materials, and have already tackled a few wall sections as follows;

2.5″ + 1.5″ of EPS Type 2
2″ + 2″ of XPS
2″XPS + 1.5″ EPS Type 2

These sheets are all lapped, and I ran the first layer horizontal and second layer vertical. I’m less concerned with these installed configurations but I’m against a budget and for the rest of the walls, I had hoped to just use two layers of 1.5″ EPS Type 2. Assuming a perm rating of 2.8/inch, are my calculations correct that 3″ would have a perm rating of 0.9333?  Should I just spring for a full 4″ EPS or 2″XPS+1.5″ EPS?

Overall, the plan is to install a service wall in front of the foam with R12 batts, then OSB to cover. Am I going down the right path? Atlantic Canada (US Zone 6?), ~noted as 4,200 heating degree days, but that seems to be trending lower past decade.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |