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Open cell foam on top of drywall ceiling

AirstreamJake | Posted in General Questions on


I have been building my own home for 2 years, and am almost to the insulating stage.

I am considering the use of 1-2 inches of open-cell spray foam on top of my drywall ceiling in order to air seal the living space below.  I would then use blown-in insulation (fiberglass or cellulose) to bring the total R-value to 40-50, which should be more than sufficient in my far northeast Texas location.  I believe that I am in Climate Zone 3a. 

The attic itself is a non-conditioned attic, ventilated with soffit vents and a ridge vent. 

No ductwork will be located in the attic, but ducts will instead be located in a crawl space that will be semi-conditioned with a single register.  The crawl space is insulated and has a concrete floor.  

The house itself has an outer layer of HardiePanel, then Tyvek Drainwrap, 1″ of polyiso rigid foam, and 1/2″ of OSB sheathing.  Between the studs, I will insulate either with blown-in fiberglass or with open cell foam.

My questions:  Is it okay and advisable to use an inch or two of spray foam to air seal the ceiling?  Would you suggest open cell or closed cell for this purpose, and why?  Could foaming the ceiling potentially cause problems with the ceiling drywall?  

Thanks to all for your help.

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  1. Expert Member
    BILL WICHERS | | #1

    There are cheaper and greener ways to air seal your ceiling. You don’t need to cover everything, only a few key locations need to be air sealed — the drywall itself is the air barrier everywhere else. The key locations needing to be sealed are usually around top plates and at plumbing and electrical penetrations. Canned foam works well for penetrations. I like to use urethane caulk on top plates when putting up drywall to seal those areas.

    Look for articles about the “airtight drywall approach” for more info. Use that method and you’ll only need the blown insulation in the attic.


  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Stephan.

    I agree with Bill. These articles may be helpful:
    How to Insulate an Attic Floor
    Attic Insulation Upgrade
    Airtight Drywall

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