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Additional question on rim joist setup

giantsean | Posted in General Questions on

Hi… I recently asked a question about insulating rim joists, and thanks for the response. In my case, because of my brick siding my back side of the house has a setup where there is a small sill within that space, making a bit of an awkward “L” shape enclosure. I have been cutting down polyiso board to 14.5×9″ squares to fit a rectangular area but wonder about the space behind it. Is it possible to fill it with fiberglass (with vapor barrier removed) and then the polyiso/foam? It seems relatively water-free but of course air gets in there. I would like to have some sort of insulation in there as there is subfloor directly above, but my main concern is trapping in moisture, which that wall is already prone to due to a chimney being built into it. Thanks again!

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  1. GBA Editor
    Martin Holladay | | #1

    Irregularly shaped areas like this are best insulated with spray foam. You can buy small cans of spray foam if you want, or you can buy a larger two-component spray foam kit. For more information on using these kits, see Basement Insulation.

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