Basement Spray Foam?

Discussion in 'Remodel Forum & Blog' started by Schopsy, Dec 11, 2012.

  1. Dana

    Dana In the trades

    Jan 14, 2009
    As long as the ratio of foam-R to fiber-R at the above grade sections is equal to or greater than the IRC 2012 prescriptive levels for exterior foam and using a closed cell foam, you're golden. 2x4 is presumed to have no more than R15, 2x6 no more than R23. So a ratio of 1/2 (R7.5-foam/R15 fiber) doesn't need OR WANT an interior side vapor retarder in US climate zone 6.

    You're either on the warm edge of zone 7 or cool edge of zone 6. With 2" of R6/inch foam you're at R12, which is PLENTY of margin with a 2x4 wall on the interior side of it. With only 1" you'd be in tough shape for the 2x6 wall in zone 7, but just fine in zone 6.

    Under no circumstances should you put an interior side poly vapor barrier (especially below grade) with a flash'n'batt approach! That will create a moisture trap and severely impede the drying rate of the assembly! If your foam/fiber ratio is too low per the IRC prescriptives, you can use a "smart vapor retarder such as Intello Plus or Certainteed MemBrain, but never polyethylene.
  2. Schopsy

    Schopsy New Member

    Dec 11, 2012
    Western Wisconsin
    Thanks Dana!
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