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

How do I attach 6″ of rigid foam insulation to a roof deck?

gchamplin | Posted in Green Building Techniques on

July 2011 Fine Homebuilding’s article about roof venting included a method for insulating cathedral ceilinged roofs with 6″ of rigid foam topped with plywood sheathing and conventional shingles. I have a roof deck of 2×6 T&G on a post and beam constructed roof. If I want to use three 2″ sheets of XPS covered with plywood, how do I attach the foam/plywood sandwich to the roof deck? Code requires a 6″ edge and 12″ field fastener pattern.

FHB example:

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. user-869687 | | #1


    Use long screws to attach the plywood. Here's a value priced screw that would work:

    Polyiso would be a better choice than XPS due to its higher R-value and much lower global warming potential.

  2. gchamplin | | #2

    Your link is for the #14 x 9" screw. I think an 8" would be the right length. What do you think of using a #12 screw. This is a low-pitched roof, (maybe 4/12) so there isn't a lot of shear force.
    Any tips on keeping the sandwich from slipping before it's screwed together. Maybe tack each layer in place with a few screws?

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |