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Questions on rim joist and poured wall insulation

jbiddle | Posted in General Questions on

I’m insulating a room in my basement to store wine.  This will not have any temp or humidity control in it, I just want to minimize the temperature fluctuations throat the year.  It’s gotten too cold in the winter and too warm in the summer (zone 6a).   The first two areas are the rim joists and the pound walls.

I removed the builder installed (1999) leftover wall fiberglass stuffed in the rim joist.  I cut 1.5″ XPS to loosely fit, glued it on, and spray foamed the gaps.
1. Should I add one more layer of 1.5″ and gap fill before a unfaced top layer?

2. Would either mineral wool or fiberglass be better for the top layer and would 3.5″ be appropriate?

I’ve added one layer of 1.5″ XPS to the poured walls and am spray foaming the perimeter.  The walls are pretty irregular and there are gaps behind the XPS.
3. Is my assumption that gaps behind the insulation are fine as long as they are sealed in with the XPS and spray foam?

4. Will building a 2×4 wall in front of the foam and insulating with unfaced mineral wool or fiberglass be a good approach?

5. is there any issue with using horizontal boards (no vapor barrier) on the face of the wall present any problems?

Thanks for any advice,

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  1. Expert Member
    Peter Yost | | #1

    Hi Jim -

    1. more than R5 rigid in rim joist: probably yes almost regardless of climate but need to know your climate

    2. Mineral wool of fiberglass for interior layer of isulation: again, need to know your climate

    3. room for air to circulate behind the rigid insulation is not a good thing BUT if there is an air seal confining those thin and small air pockets, you should be fine.

    4. insulation to install in stud wall: again, need to know climate. While the below-grade portion of your foundation wall won't be a problem for almost any level of total insulation, it's the above-grade portion that sees the full delta-T that needs the proper proportions of air permeable/air impermeable to avoid condensation potential.

    5. face of the wall interior finish is boards: how much of a vapor retarder you need is dependent on climate and really only relevant for that above-grade portion of the wall.


    1. jbiddle | | #2

      Climate Zone 5, I guess...southeast Michigan

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