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Closed-cell vs. open-cell spray foam and exterior rigid foam on the roof

mcaudill | Posted in Energy Efficiency and Durability on

In climate zone 5 if you use a roof wrap, rigid insulation and a vented area under a metal roof on top of the roof sheathing, then is open cell foam better for the underside of the sheathing since it would allow the roof sheathing to dry out – OR – would a closed cell foam or other vapor barrier still be needed? Thanks.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Michael,
    If you plan to install rigid foam above your roof sheathing, then open-cell spray foam is a better choice than closed-cell spray foam on the underside of your roof sheathing. If your roof sheathing ever gets wet, the open-cell spray foam will allow the damp sheathing to dry to the interior.

    For more information, see How to Install Rigid Foam On Top of Roof Sheathing.

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