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Community and Q&A

What insulation for band joists between floors?

whitenack | Posted in Green Building Techniques on

Hi all,

We have a super-insulated home in zone 4a. 3″ of polyiso on the outside, then damp blown cellulose between 2×6 studs, 16″oc.

What do people use to insulate in the band joists between the 1st and 2nd floor? The concern I had about using blown cellulose there is whether the cellulose would stay firmly in place over time. In the walls, you have the drywall keeping it from crumbling out too much. However, there wouldn’t be anything holding in the insulation in the band joists.

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  1. GBA Editor
    Martin Holladay | | #1

    The exterior polyiso gives you lots of latitude -- you don't have to worry about potential moisture accumulation in the rim joists. Most builders would insulate these rim joists on the interior with fiberglass batts or mineral wool batts.

    -- Martin Holladay

  2. Expert Member
    ARMANDO COBO | | #2

    We use rigid foam on the outside of the wall assembly, and since we always use floor trusses, we spray open cell foam. I find batts or BIBs very difficult to do right, specially around webs.

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