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Cellulose below grade?

eyremountllc | Posted in Green Products and Materials on

We have a Superior Walls basement which we are trying to add more insulation to, as part of our Passive House thermal envelope. We’ve added 2″ of EPS outsulation to mitigate the thermal bridging caused by those concrete studs.

Other than that, the walls do provide 6-inch deep cavities which we can fill with insulation. Our initial thought was cellulose. But we are concerned about moisture potential below grade. I know the EPS outsulation helps move the the dew point out, but is it safe to use cellulose below grade?


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  1. jklingel | | #1

    Where are you? How wet is your soil? Etc.

  2. GBA Editor
    Martin Holladay | | #2

    My advice: don't do it. Below grade, stick with spray foam or rigid foam.

    If you absolutely don't want to use foam, and you are confident that the wall will stay dry, you could use mineral wool (Roxul or Thermafiber).

  3. eyremountllc | | #3

    We are in the D.C. area. I think the safe bet is rigid foam too. Thanks for the confirmation.

  4. wjrobinson | | #4

    5,000 psi concrete is called watertight by Superior. The one that I worked on was indeed such. Fiberglass over foam would work too via BSC. These walls are not porous and prone to moisture like block walls. Martins materials cost more and are safer but may not be needed. I agree with no to cellulose.

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