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Community and Q&A

Whether or not to insulate open joist bays between 1st and 2nd floors .

Susan Deissleider | Posted in General Questions on

So far Erik North’s Free Energy Maine blog/website has been the only site that actually answers the question about whether or not to insulate open joist bays between 1st and 2nd floors on his blog post “Should I Insulate Between Floors?”. I tried posting a comment on the blog page looking to get his suggestions what is the way best resolve this issue, but it doesn’t go through.

His site led me to the Green Building Advisor webpage, so I am hoping that someone here would be able to provide me with some helpful advice.

The house is a 1950 era ranch on a slab with a 2nd floor addition added late 1960’s located in southern New England. The first floor is approx. 1200 sq. ft. and the 2nd floor is approx. 1000 sq ft. in area. The first floor eaves are fully open with fully vented vinyl siding soffit panels with no insulation between 1st/2nd floor 2×6 joist studs nor is there any weather/air seal at the joist bay ends.

I am looking for opinions/options as to what is the best way to resolve this issue?

I’ve come across a few Home DIY message boards that suggest using faced batts insulation at each end of the joists. Seems like a possible solution if Tyvek or another vapor barrier is used to weather/air seal the joist bay ends.

Another would be to use blown in fiberglass or cellulose, but then wouldn’t the lack of a vapor above the 1st floor ceiling sheet rock be an issue?

Any insight/help would be greatly appreciated.



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  1. GBA Editor
    Martin Holladay | | #1

    Your question is confusing. At one point you refer to "2x6 joist studs."

    There is no such thing as a "joist stud."

    Are these joists (horizontal framing members for floors) or studs (vertical framing members for walls)?

    We need to know:

    1. Are your stud bays insulated or uninsulated?

    2. Are you asking for advice on insulating the rim joist area, or are you asking for advice on insulating the entire joist bay volume that separates your first floor ceiling from the subfloor on the second floor?

    If you are looking for advice on insulating the rim joist area, you may want to read this article: Insulating rim joists.

  2. Charlie Sullivan | | #2

    It sounds like you might have the roof overhang from the original first floor roof, with soffit venting, and then the second floor wall set back from that roof by some distance. It's hard to know where to start in answering without more details.

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