DIY Home Improvement Forum banner

Questions about adding eps on top of xps?

600 Views 4 Replies 4 Participants Last post by  carpdad
I want to add more insulation to the stud bays in the unfinished area of my basement after learning that xps eventually looses half of its r value. They sell 3/4 inch eps already sized close to my needs. The rim joist and above ground stud bays have 2 inch xps. The builder left fiber glass and vapor barrier exposed but I suspected it was getting moldy so I replaced with xps and added dehumidifier.

My question is there any issue layering eps with xps? Should the eps go flat against the existing foam or would it be beneficial to leave a air gap? I locked the other sheets in with spray foam and that could easily provide some spacing. Seems it would be a good idea to drywall it as well.

The finished area only has the thin xps against the foundation walls and 2 inch on above ground bays. I didn't realize how beneficial it would have been to have 2 inch xps against the foundation as well. I'm in northern IL.

I can at least improve the unfinished area. I might eventually frame walls against the rest of the foundation but it would only be for insulating properties. I now know that saves a lot on heating costs but does it affect cooling in the summer?

1 - 2 of 5 Posts
thanks for the replies.

After more research and reading some articles on green building advisor their term of cut and cobble to fill stud bays with foam is not a good practice although its a good option for the rim joist area. My current plan is to switch out the foam for rock wool and cover with something like membrain and drywall. I've read its good to caulk all around where the studs meet the sheathing.

What I'm uncertain about is how critical it would be to seal and over lap the membrain? If I understand correctly sealing the membrain perfectly doesnt matter so much if you caulk the stud sheathing joints and make that air right.

I would like to insulate the rest of my foundation walls but dont want it finished. I might consider doing something like dow thermax glued on. I don't think this stuff has to be covered?
See less See more
1 - 2 of 5 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.