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subfloor OSB exposure

carsonb | Posted in General Questions on

hi GBA’ers,
for the construction folks out there, what would you consider normal exposure levels for OSB subflooring?  The subflooring has been left exposed for 5 months now due to delays and it’s showing quite a bit of flaking, discoloration, and raised edges.  The brand is durastrand.  According to the durastrand website Q&A they brush off any moisture issues as purely cosmetic and you should just sand them.  Should I be concerned about long term issues?  In at least one place where things were put on top of them, I saw some mildew/mold, probably small enough to be sanded off but still concerning.

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  1. Expert Member
    BILL WICHERS | | #1

    Staining of the surface is not a problem. Mold looks bad and should probably be cleaned, but isn’t itself a problem for the structural stability of the material (although it may be an indicator that the material has seen excessive moisture which CAN be a problem). Minor expansion of the edge is probably not an issue unless it’s getting pretty far into the problem.

    The pic that concerns me most is the one in the lower left. That shows possible deterioration of the panels. I’d check those panels to make sure they’re still ok structurally.

    The worst thing that can happen is for water to pool on top of the panels and keep them soaking for extended periods of time. Water that quickly runs off and doesn’t have a chance to soak in is less of a problem.


    1. carsonb | | #2

      Thanks Bill,
      How would I determine their structural stability? I’m guessing jumping on them isn’t sufficient. The lower left image is a zoomed in image of swelling, one panel raised about 1/8” at the edge, and seems typical on many of the panels. The fibers you see are mostly debris from construction, hopefully that is what concerned you the most. The water doesn’t pool up as it’s a flat deck, but still has likely had quite a bit of water on it after a storm as the roof isn’t on yet.

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