On Sat, 23 Apr 2016 15:01:46 -0700 (PDT), Fredd Wright
wrote:

I have a crawlspace in the basement that has a dirt floor right now. I'd like to lay some sheets of 4x8 plywood (or other material) on it to make a surface suitable for crawling on or putting things on. It will lay right on top of dirt. It doesn't have to look good as it's in a crawlspace in an unfinished basement. I't won't be exposed to rain but there will be some moisture coming up through the dirt. Also, i'm probably going to hose it off occasionally. In addition, every 5 years or so it will be underwater for a day or two when we get a hurricane as they usually flood the basement. Can anyone recommend something that will last but not cost me an arm and a leg? Again, i don't care how it looks.

If it's a very dry crawlspace, perhaps PT ply, preferably something
that's rated for ground contact. Other than that, PT 2x4s for
stringers with PT ply on them. Even if it's dry, the humidity may be
quite high, hence the PT.