GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X 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

Rigid Foam on Attic Floor?

brrowle | Posted in General Questions on

Hi there,

I’ve been reading a lot about upgrading the attic insulation in my single floor zone 5 home.  My first stop has been air sealing my attic, which has so far proved to be fairly miserable work with the number of penetrations we have.

As I’ve been up there working, I’ve wondered to myself: is there any reason I can’t lay a level of polyiso foam across the joists on the attic floor, close off this toping at the top plate of the exterior wall, and then put unfaced batts across this topping for additional insulation?

Am I missing something or would this be a reasonable way to air seal and insulate all in one?  Sorry if this has been written about, but I haven’t seen anything on this specific topic!

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.


  1. Expert Member
    BILL WICHERS | | #1

    Sure, you could do that, but it's a lot more of that miserable attic work you're trying to avoid. If you've already done your air sealing work, just blown in a layer of loose fill cellulose and call it done. Loose fill insulation is much better than batts, it's cheaper, and it installs a whole lot more easily too. You have to air seal either way, so it's best to just air seal the "regular" way, sealing benetrations and gaps in the attic floor, then cover everything with loose fill "blown" insulation for the "insulation" part.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |