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

How much air space to roof deck with only R10 above the top plate?

mikeolder | Posted in General Questions on

The ends of my 2×2 trusses are 3″ tall, so I have that small space to work with.  

How much of a air gap should I leave between the foam and the roof decking?   Any suggestions on how to cut the foam to that shape would be appreciated as well. 

Thanks!

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. Expert Member
    Michael Maines | | #1

    The IRC specifies a minimum 1" vent space; though famously based on flimsy evidence, it seems to work and it's the least I would do. If possible, I would add insulation on the interior by furring down the ceiling at the eaves.

    1. mikeolder | | #2

      But that last 1" would be another R6 and I wonder with only a 3" space if utilizing the air space for insulation is a better approach because R14 wont stop melting or ice damns anyway. What insulation board would you recommend given the small space that opens up to 14"? Polyiso?

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |