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Bringing ducting into the thermal envelope

Michael Cicero | Posted in General Questions on

I got a quote to spray foam under the roof sheathing to bring the ducting in an attic space into the thermal envelope.  He provided 2 quotes, one of open cell and one of closed.  I know the potential dangers with open cell and rotting the sheathing, but the cost is cheaper and they would insulate the rafters to help eliminate thermal bridging.  Is the thickness at 10 inches enough to provide a safety factor against possible sheathing rot or should I eat the cost and make sure I am safe?  I attached both proposals.  Thanks

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Replies

  1. Expert Member
    Akos | | #1

    Depends on the climate you are in:
    https://www.energyvanguard.com/blog/75042/Will-Open-Cell-Spray-Foam-Insulation-Really-Rot-Your-Roof

    The closed cell+batts is the safer approach.

    1. Michael Cicero | | #2

      I am in climate zone 6A.

      1. Alex P | | #3

        From the article
        "Don't use open-cell spray foam in cold climates (IECC climate zones 5 and higher) without a vapor retarder."

  2. GBA Editor
    Brian Pontolilo | | #4

    HI Michael.

    Good advice here from Akos and and Alex. You mat find the recommendations in this article helpful too: https://www.greenbuildingadvisor.com/article/open-cell-spray-foam-and-damp-roof-sheathing.

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