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Can I use spray foam on a ceiling that also serves as the roof under a deck?

TDHunt | Posted in General Questions on

I am replacing an exterior deck over a sunroom.due to leaks in some old EPDM material under a deck.

The sunroom ceiling joists support the flat roof above it, and the deck is suspended above the flat, EPDM covered roof. Can I spray the sunroom ceiling jousts with foam before installing the sunroom headboard ceiling? Would this produce condensation into the sunroom ceiling? The deck above is outside and exposed to summer heat and winter snow.


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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Can I use spray foam on a ceiling that also serves as the roof under a deck?"

    A. Yes. All of the usual rules for spray foam jobs apply, of course: the roof decking must be sound and dry, and the spray foam layer must provide the minimum R-value required by your local building code. (In the U.S., this ranges from R-30 in Florida to R-49 in the northern half of the country.) Once the spray foam has cured, it needs to be protected on the interior with a layer of 1/2-inch drywall.

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