Some background -

  • I bought my current house in the middle of a drought in 2007, and knew nothing of vapor barriers.
  • The house has a nice, albeit uneven crawlspace, that is walkable for about half of it's size.
  • I built a floor with two by fours and osb for a workshop in about one third of the crawlspace
  • The rest is just dirt.
  • I'm in the hot and humid American Southeast.

I've come to the realization that I need to add a vapor barrier in the crawlspace to bring the humidity and mustiness down. Putting down plastic sheeting over the non-workshop part of the crawlspace should be no problem, but I reallllllllllllllly don't want to pull up the flooring of the woodshop, put plastic down, and put the flooring back down again.

Is it possible that the OSB would do at least some of the traditional plastic sheeting vapor barrier?

The dirt floor as it stands now.

  • OSB has no business in damp or very humid locations. While the adhesive it's made with is technically rated for exterior use, the nature of the wood "strands" in the product are highly prone to swelling and eventual delamination. At a minimum, use exterior (CDX) plywood.
    – isherwood
    Commented Jul 17, 2017 at 18:27
  • This is a pretty low priority area - it's basically just storage and tools sitting on the osb. Commented Jul 20, 2017 at 14:28

1 Answer 1


Moisture barriers are not a water tight seal kind of thing.

If you cover 75% of the dirt then you should reduce the mustiness by about that much.

Anything will probably be an improvement and if is not good enough you could paint the OSB floor to add some moisture barrier. However, this could possibly reduce the life of the OSB since it can't breath as well.

Good luck!

  • I agree with the first sentence, but not the second. A large-ish area of exposed soil, regardless of the proportion of the total area, could easily release enough moisture to saturate the air and produce condensation. That's all it takes to sustain mildew, etc.
    – isherwood
    Commented Jul 17, 2017 at 18:28

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