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My house had carpets over 5/8 particle board that was sitting on top of 1/2 plywood subfloors. I've removed the particle board and was thinking of installing 5/8 OSB before putting down 3/4 hardwood flooring since I've read that 1/2 subfloors are not thick enough for hardwood. First question, is that the right approach? Is 5/8 absolutely necessary or can I get away with something thinner and less costly?

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Modern homes are often built with 3/4" OSB subfloors. This is the minimum standard, in my opinion, and it's what you need to achieve. Solid hardwood flooring adds considerable stiffness itself, but only where it runs perpendicular to the joists. That may not be the case everywhere, so you need to get to that minimum standard.

I would probably add 1/2" OSB or CDX plywood. You don't need a smooth surface, so you don't need to pay for B-grade plywood, for example. Just adding 1/4" material wouldn't achieve the same level of stiffness that a single 3/4" subfloor would (unless you were to completely bond the two layers with adhesive). 3/8" plywood would also probably suffice.

I suggest that you run whatever plan you choose by your flooring installer. Any warranty will depend on a proper subfloor, and some more scrupulous installers won't even do the job if they're not happy with what you have.

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  • Thank you for your answer. Would you suggest using screws to attach the second layer to the joists? Commented Nov 13, 2023 at 23:49
  • Fixing the second layer using glue and screws would be better, quieter and stiffer.
    – handyman
    Commented Nov 15, 2023 at 22:20
  • Screws or ring-shank pneumatically-driven nails, along with construction adhesive.
    – isherwood
    Commented Nov 15, 2023 at 22:21

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