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Flash and Batt foam thickness

MMargulies| Posted inEnergy Efficiency and Durabilityon

I’m in NJ climate zone 5 and have a project with an installed falsh and batt with 1″ closed cell foam and Roxul batt in wood framing. I usually spec 2″+ but would like to avoid ripping everything apart and spraying more foam. Is there a chart/rule-of-thumb anywhere showing wtih of foam based on climate zone averages or any specific data to justify thickness besides doing a calc? This seems like a case where it would probably be ok but with a small chance for a big problem??

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Replies

  1. GBA Editor
    Martin Holladay||#1

    Michael,
    Relax -- your walls should be fine.

    The guidelines you are looking for can be found in either of these two articles:

    Calculating the Minimum Thickness of Rigid Foam Sheathing(Look for the paragraph with the headline, "What about flash-and-batt jobs?")

    Why Flash and Batt Makes Sense("According to building scientist Joseph Lstiburek, flash-and-batt installations require at least 1 inch of spray foam in climate zone 5, 1 1⁄2 inch in zone 6, and 2 inches in zone 7.")

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