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

Cathedral ceiling insulation

5grams | Posted in General Questions on

Good Afternoon,

I had posted a previous question regarding insulating a new construction vaulted ceiling (2×12 raftered) in Michigan (zone 5).  Exterior roof is standing seam metal roofing over osb covered with ice & water shield.  There is no exterior insulation, due to our poor planning.

From piecing together your and Dana’s previous recommendations we have decided to make this roof “hot” using 5.5″ closed cell foam sprayed directly to underside of osb sheathing.  We will fill the remaining ceiling cavity with  R-23 rockwool (5.5″) and covered with 1/2″ drywall.

I have deduced from reading many of your recommendations that we should NOT install a vapor barrier below the rockwool.  Is this correct?  Do we need any kind of vapor retarder, either a film or in the paint?  Do you see any problems with our plan?

Thank you for your help!

Katie G.

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

    Katie,
    Your plan will work. You don't need an interior vapor retarder or vapor barrier. However, you should strive to make your ceiling airtight.

    For more information, see "Flash-and-Batt Insulation."

  2. 5grams | | #2

    Thank you, Martin!

  3. Peter Yost | | #3

    Hi Katie -

    And try to keep your interior relative humidity as low as you can for your comfort and the buildings...in the winter (30% would be best but no higher than 40%).

    Peter

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |