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Basement sheathing – mold

user-6651407 | Posted in General Questions on

We have a small wall section in our basement that is not yet insulated.  It has a water pipe running to the outside.  It’s been on our list to insulate, but some reason it didn’t happen yet.

After the frigid temps in the Midwest, reaching -30 with windchill, I was checking the basement and noticed mold on the sheathing in this spot.

Its only around the water pipe/nails. No where else on the length of the wall.  We already removed the mold. But before I insulate, I want to make sure I solve the problem.

Would you believe this to be a water instruction problem?  I checked this same spot after heavy rains in the summer and it always was dry.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Birdie,
    The source of the moisture is probably indoor air. For a discussion of the phenomenon, see this article: "Condensation on Wall Sheathing During Construction."

  2. user-6651407 | | #2

    Thank you.
    The rest of the walls have open cell spray foam, no drywall yet.
    Should I assume all these walls are bad?

    1. GBA Editor
      Martin Holladay | | #3

      Birdie,
      Open-cell spray foam is an air barrier. The spray foam prevents indoor air from directly contacting the cold sheathing, and therefore prevents condensation. Some moisture accumulation in the sheathing is possible (due to outward vapor diffusion through the foam), but mold is unlikely.

      1. user-6651407 | | #4

        Thank you for your time. Very much appreciated.

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