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Best air sealing and insulation for knee walls in tray ceiling


I have a single family home in climate zone 5B.The attic is ventilated. I had the attic air sealed and insulated to R50 with blown in cellulose 1 year ago. It looks like they neglected to do the knee walls properly on the great room which has a tray ceiling which is 3 feet high (see photo). They just wrapped the knee walls with batt insulation and otherwise didn't do anything else.

1. What would be the best options to air seal and insulate the knee walls?
2. Is this difficult to do since the attic now looks like a winter wonderland?

Thank you

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Asked by Stan Weinstein
Posted Jan 11, 2017 1:06 PM ET


3 Answers

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If batt insulation was used for the kneewalls of the tray ceiling, you need to make sure (a) that the batt insulation was installed without voids, (b) that there is an air barrier on the attic side of the kneewalls, and (c) that the R-value of the batts is adequate. (I'd want more than the R-value used for a typical exterior wall, because this is part of a ceiling assembly.)

If the job was botched, there is always a way to fix it and do it right. It may not be easy, but anything is fixable.

Answered by Martin Holladay
Posted Jan 11, 2017 2:06 PM ET


Thanks Martin....there are voids in the batt insulation and there is not an air barrier.

Trying to make sure the next time someone is up there it is done right. Would closed cell spray foam and/or rigid foam board be a good option? What would be your preferred method if starting from scratch?


Answered by Stan Weinstein
Posted Jan 11, 2017 2:33 PM ET


Almost any type of insulation will work here, as long as the installation is competent and the R-value is adequate.

I would probably build extra framing (in essence, a double-stud wall) to provide a wide cavity to allow enough room for lots of fluffy insulation (held in place by InsulWeb, housewrap, or rigid foam on the attic side).

Answered by Martin Holladay
Posted Jan 11, 2017 2:57 PM ET

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