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Community and Q&A

Spray Foam in Hot-Humid Climate

sdp07d | Posted in Energy Efficiency and Durability on

I am looking into installing spray foam in my roof deck in a hot and humid climate. I was planning on spray foaming the attic for both my house and the attached garage and shared wall within the attic.

Based on some recent reading, I am hesitant in using open cell due to humidity rising and sustaining the roof deck. I’ve read that air conditioning within the attic can reduce these problems

Will open cell foam inside an attic be ok over an unconditioned space such as the garage? Sounds that be loose fill or close celled foam?

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  1. sdp07d | | #1


  2. user-2310254 | | #2

    Here is my non-expert input. A flash and batt approach (close cell foam with air permeable insulation) is safer from a moisture-management standpoint. Installing all closed cell is similarly less risky (if not particularly green). But it is probably easier and cheaper to install open cell foam.

    With open cell, it is important to monitor conditions in the attic space. If moisture is consistently too high, you should take steps to manage this issue. Managing moisture may involve introducing conditioned air, additional air sealing, and mechanical dehumidification.

    1. JC72 | | #3

      ^^^ This in spades

    2. sdp07d | | #4

      Thank you. It sounds like I'd be better off with closed cell flash and batts over my garage and I might be able to get away with open cell over my living space.

      What are the risks of closed cell if a roof begins to leak or for termites, are they any different than open cell?

      1. Expert Member
        BILL WICHERS | | #5

        There isn't much difference in terms of risks to the structure from closed cell or open cell spray foam. Using all closed cell here is safest, but you could also use enough closed cell for vapor control and then finish off the rest with open cell to save a little money. Chances are there won't be a huge cost difference though, so I'd just go with closed cell here.


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