I am in the process of finishing the upstairs of our story and a half house and I am curious if I need to worry about laying another layer of sub-floor down. When they built the house they put down a layer of 3/4" T&G OSB, glued and nailed. About half of this was exposed to weather for a short time (4-6 weeks of summer rain and sun) Where it was exposed it is a lot grayer than the "newer" stuff that didn't get exposed so much. I have noticed some uneveness but I do not know how much is too much. I plan on putting down padding and carpet and also tile in some places and to be honest I wouldn't rule out some hardwood floors as well. Do I need to add another 1/2" of plywood or something else or do I not need to worry at all? I am no where near complete, but you have to think of these things so far in advance for rough openings for doors and such.