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Zone 2 insulation question

jam1030 | Posted in General Questions on

I’m need to insulate an elevated floor in zone 2. Code in my area states R13. I plan insulate rim joist and bottom of joist with 1” polyiso taped and sealed with spray foam. However, this only gives me R6. The 2” polyiso is not available in my area!
Any suggestions on adding additional insulation to get to R13? My floor joists are 2×12’s

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Jam1030.

    You can either install two sheets of polyiso with staggered seams, or add insulation to the joist bays, which could be cellulose, fiberglass, mineral wool, etc. I assume from your other questions that this is a raised floor that is open below, perhaps on piers, in which case you should consider protecting the insulation with a layer of OSB or plywood. And remember that air sealing is just as important as R-value. I suggest you read this: Insulating a Wood-Framed Floor Assembly

    1. jam1030 | | #2

      It is raised and open underneath. I was thinking of adding fiberglass between joists and add the 1” polyiso on bottom to seal off an protect fiberglass.
      How would you use cellulose in this application? Seal off bottom and then blow in through holes above in subfloor?

      1. GBA Editor
        Brian Pontolilo | | #3

        If it were new construction, you could blow cellulose in before laying subflooring. On a retrofit, yes, you would need to determine the most appropriate place to make holes or find a way to open the floor to blow it in.

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