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Basement insulation question

| Posted in General Questions on

Ready to put up sheetrock in my basement.  I live in zone 5a (NJ) and have installed 1″ XPS and paper faced batt insulation between the 2×4’s.  However, I’m getting conflicting info on whether the mineral insulation should be faced or unfaced.  Can anyone shed any light on this?  Before I put up the sheetrock, I can rip off the paper or slice some holes in it w/ a razor if need be.

Insight is greatly appreciated!

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Replies

  1. Expert Member
    Peter Yost | | #1

    Hi XXXX (be great to have a name for the GBA Q&A community to use) -

    Interesting question. The vapor permeability of kraft paper facings on fiberglass batts is in the range of 0.4 - 4.2 perms (see https://www2.owenscorning.com/literature/pdfs/10017860%20Moisture%20Control%20Perform%20Kraft-Asphalt%20Facing%20Tech%20Bulletin.pdf). It's vapor permeabliity is variable, ostensibly qualifying it as a "smart" vapor retarder. And classifying this facing as a Class II to III vapor retarder.

    You don't need a vapor retarder beyond Class III for this basement wall and you certainly don't want a Class I vapor retarder here (see: https://basc.pnnl.gov/resource-guides/no-vapor-retarders-interior-side-air-permeable-foundation-insulation).

    But the facing retarder is ok to stay or go in my book.

    Peter

  2. Expert Member
    Peter Yost | | #2

    Hi XXXX (be great to have a name for the GBA Q&A community to use) -

    Interesting question. The vapor permeability of kraft paper facings on fiberglass batts is in the range of 0.4 - 4.2 perms (see https://www2.owenscorning.com/literature/pdfs/10017860%20Moisture%20Control%20Perform%20Kraft-Asphalt%20Facing%20Tech%20Bulletin.pdf). It's vapor permeabliity is variable, ostensibly qualifying it as a "smart" vapor retarder. And classifying this facing as a Class II to III vapor retarder.

    You don't need a vapor retarder beyond Class III for this basement wall and you certainly don't want a Class I vapor retarder here (see: https://basc.pnnl.gov/resource-guides/no-vapor-retarders-interior-side-air-permeable-foundation-insulation).

    But the facing retarder is ok to stay or go in my book.

    Peter

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