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

Exterior foam substitute above thermal envelope on attic wall

John Ranson | Posted in Green Building Techniques on

Hi,

I’m planning 4″ of exterior rigid foam on my walls with a cellulose insulated attic floor. My WRB is outside my rigid foam. Because design uses a monoslope roof, there’s a large portion of attic wall that’s above the thermal envelope of the house. In this area, are there any good assemblies that I can substitute for the rigid foam? My hope would be to reduce labor and use less foam.

–John

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.

Replies

  1. GBA Editor
    Martin Holladay | | #1

    John,
    The answer depends in part on your siding choice, and whether or not you intend to install vertical furring strips.

    If you are installing 1/2" plywood furring strips over your 4 inches of rigid foam, you could, in theory, install three layers of 2x4s as furring strips on your attic wall. That makes the furring strips co-planar.

    To me, this approach is costly, fussy, and not worth the trouble. I would just install 4 inches of rigid foam over everything. If you want to save money, buy recycled (reclaimed) rigid foam.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |