I'm redoing an attic and the daughter-in-law wants to put down a floating, interlocking wood floor. House is 60 years old with 3/4"x4" tongue and groove pine floor. I have enough sheets of 1/2"? OSB, that I used as flooring in the kneewall storage areas, to use as underlayment. But I see that people here mention 1/4" 'underlayment plywood'. Is that what I should be using? And I guess just a long enough nail to go through the T&G and into the joists? Thanks.