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

Poly on the warm side of drywall

cabinflyer | Posted in Energy Efficiency and Durability on

OK team….

I need a question answered, kind of ASAP!

I just acquired a single story 1200 sq ft rental. It has roof trusses, and below the trusses is a drywall ceiling. Below the drywall is a suspended ceiling. As part of an energy upgrade, I am installing 2′ of loose fill cellulose in the attic (ceiling).

We discovered that there was no vapor barrier (poly) above the drywall. No problem EXCEPT the drywall was never taped…or anything! ( I guess hence the false ceiling). No problem except my drywall guy says it will be VERY expensive and time consuming to try and do repairs the drywall. Drywall replacement is not really an option.

So…We came up with a plan to replace the old suspended ceiling with 2×3 nailers below the drywall and then nail some surplus T&G pine paneling to the nailers. I know…this alone does nothing to address the air movement/vapor issues.

My insulation guy thinks we would be ok to put 4-6mil poly between the untreated drywall and the nailers and do a good job of taping the poly to endure no leaks. Combined with the nailers keeping the poly secure, He feels if any moisture got behind the poly it would continue up thru the cracks in the old drywall to the cellulose and up to the cold roof.

Zone 7 7000 HDD.



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. lance_p | | #1

    Could you just tape the drywall seams, either with compound and tape or with some sort of air sealing tape?

    What about just finishing the drywall (instead of building another false ceiling)? If it's in bad shape what about putting up fresh drywall over it and finishing that?

  2. Expert Member
    Michael Maines | | #2

    Steve, if the attic is properly vented, that is a reasonably safe place to put poly sheeting, as long as you're not in a location that needs air conditioning for long stretches. (Only 7000 HDD days in zone 7 makes me think you might be in central Colorado?)

    If the drywall is painted, as Lance suggests you could just tape the seams (3M 8067 would be a good choice).

    If you want better vapor control, you could use a variable permeance membrane. The most affordable (and flimsiest) is Certainteed Membrain. Pro Clima Intello and Siga Majrex are much tougher, but might be overkill for your situation.

  3. cabinflyer | | #3

    Yes the attic is now properly vented. After watching a video from the CCHRS we put up 6mil poly and caulked AND taped all the seams. We then put up 2x3 nailers below the poly. The drywall basically will now act as a brace to hold back the 24" of loose fill cellulose. It all looks pretty good

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |