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

Flash and batt for attic floor

medrep366| Posted inEnergy Efficiency and Durabilityon

I live in zone 7, old construction. Currently the attic i floor is insulated with fiberglass batts, obviously creating lots of problems with heat loss and ice forming on the roof under certain conditions. The roof itself isn’t insulated, so it’s a ventilated attic.
I’ve been offered to replace the batts with 4″ of closed cell spray-polyurethane foam. I am considering an alternative with a 2″ layer of closed cell foam followed by 5″ of fiberglass batts. This would save some money for me, especially given that I already have the batts. My understanding is that since I live in the cold climate, water vapors would be moving from the house to the outside for most of the time, and the closed cell foam would prevent them from escaping. Therefore the dew point issue is not relevant.
Any comments/ideas from the pros?
Thank you.

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

    Oleg,
    The method you describe works well. Two inches of closed-cell spray foam does a good job of air sealing a ceiling.

    My only recommendation is that you scrimp, save, or borrow the money to add more insulation on top of the cured spray foam. If you could afford to install 12 to 16 inches of cellulose on top of the foam, you'd have a well insulated ceiling.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |