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Embedded rim joist insulation

michaeldrehl | Posted in General Questions on

I have a house that was built around 1895 in Northern NJ. The rim joists are not insulated at all. The floor joist rest on the brick foundation and are embedded into the rim joist. Please see the photo attached.
The floor joists are cupping in certain areas of the house.
I was wondering how I can insulate the joists. On the outside, there’s aluminium siding with clapboards. You can’t see the rim joists from the outside, they are hidden by the siding.
I want to insulate but not want to see any mold growth since they need to dry out to the inside.

Thanks for any help.

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  1. michaeldrehl | | #1

    I am in northern NJ and the house is sort of balloon framed. The stud cavities looking up from the basement and first floor are hidden by the flooring. However, from the roof you can look down and you can see the second floor flooring.
    Thank for any help.

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Michael.

    Rim joists don't necessarily need to be able to dry inward. If the rim joist is not getting wet from rain (and if it is, that needs to be fixed first), then vapor-impermeable interior insulation like rigid foam and closed-cell spray foam is generally okay to use.

    What's more concerning about your situation may be the lack of a capillary break between the foundation walls and the framing. If these is no sill seal to prevent the framing from wicking moisture, the framing can get and stay wet, which can cause mold and rot. You can test the framing with a moisture meter before making a decision on how to go forward. It still may be okay to insulate if the framing is staying dry.

    This article may be helpful: Insulating Rim Joists

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