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Condensation above ceiling when you live in the attic?

Yonah | Posted in General Questions on

I moved into a New York City two floor house. The “third” floor is really a conditioned, finished attic, which is now a master bedroom. The walls and ceiling in the attic are covered in painted sheetrock. I suspect that there is insulation behind all of the sheetrock, because in the slanted side rooms of the attic (where there is no sheetrock), which are like crawlspace storage rooms, I do see insulation with foil backing. So, hopefully the same exists above the ceiling sheetrock too.

Do I have to be concerned about the warm room air in the winter causing condensation as it hits the wood holding up the roof? (Obviously that is very much hidden from view.)
In the worst case scenario that there is no insulation, would the painted sheetrock ceiling act as a vapor barrier?

I appreciate any advice I can get.

Thank you.


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  1. Expert Member
    Dana Dorsett | | #1

    Foil facers are vapor barriers, but if there is air leakage convecting humid conditioned space air to the cold roof deck it'll move orders of magnitude more moisture up there than mere vapor diffusion through painted wallboard. If there is a ventilation space between the insulation and the roof deck that has openings to the great outdoors the moisture will head outdoors, even with minor to moderate air leakage. (Though with moderate to high air leakage you can end up with wet insulation along the exfiltration path.)

    If there is no insulation the roof deck will be warm enough to avoid absorbing much moisture, and would dry quickly in the spring, but it's a heluva heat loss.

    Hopefully there is a vented roof deck, ESPECIALLY if they used foil faced batts everywhere. Without the venting the foil facer & roofing material are a moisture trap, with a fairly high risk of developing mold & rot problems. In one of the mini-attic crawlspaces peel one of the batts back a bit, and see if there is at least an inch of space between the insulation in the roof deck. If yes, put it back, taking care to seal it. (You may have to tape it with housewrap tape or a high quality aluminum tape for a long term air seal.) Report back what you find.

    If there is no insulation the ceiling would be quite warm, even hot to the touch in summer when the sun is hitting the roof. With even R13 in there it won't feel hot, but it'll be warm when sun-drenched.

  2. GBA Editor
    Martin Holladay | | #2

    You can always drill some holes in your drywall ceiling and investigate with a coat hanger wire and a flashlight. (Be careful to avoid any electrical wiring.)

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