It depends what kind of subfloor you have already, if it's straight on to the joists then it would probably be best to fix ply and have the OSB as a floating floor. The only place they use OSB as the subfloor is new builds because it's cheaper but it will definitely start flexing and creaking, so avoid if possible.
It depends what kind of subfloor you have already, if it's straight on to the joists then it would probably be best to fix ply and have the OSB as a floating floor. The only place they use OSB as the subfloor is new builds because it's cheaper but it will definitely start flexing and creaking, so avoid if possible.