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New Construction un-vented roof

TheSkycrane | Posted in Energy Efficiency and Durability on

Hello! I have researched the website over the past few months and I have some design questions that haven’t been answered or at least not what I have seen. I am building a home, roof is galvalume metal unvented on a purlin system. Synthetic underlayment under that and 1/2 osb is my roof decking. I see mixed information on closed cell vs open cell. I am thinking it’s going to be closed cell, does it need a vapor barrier then? I m in central Florida zone 2. Also do I condition the space or not?

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  1. nlrlayton | | #1

    I have the exact situation and would like to hear advice. Thank you

  2. Expert Member


    You may find this article useful:

    My takeaway from discussions here on GBA is that if you can keep the humidity in the attic very low, open cell foam may work. Closed cell foam doesn't have that caveat on its use. In either case conditioning the attic is a must.

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