I want to raise my subfloor by about 1/4 before installing my new hardwood floor but I can't seem to find clear instructions on how to do that... It's an OSB subfloor and I'm thinking of using either a 3 ply 5.5 mm Home Depot poplar plywood (cheap) or a 5 ply baltic birch (3x the price). What is the recommendation on which material to use?
I'm also looking on info about how to install. Should I put down some #15 felt paper between subfloor and underlayment or should that go above the underlayment directly under the hardwood floor (or nothing at all). And lastly can I just use a pneumatic finish nailer?