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We are doing a hardwood installation project. So far this has involved removing carpet and particle board to get down to the 1/2" plywood subfloor. The subfloor seems to be in a good shape, so I'm happy about that. Now I've been told I need to add a layer of OSB and then the hardwood. So here are my questions:

Do I really need to add this OSB? Is it a matter of strength or just a matter of floor-height? Seems like the particle board wasn't adding much, strength-wise, and maybe adding 3/4" hardwood over 1/2" subfloor wound suffice. Since I'm doing the whole house, the floor height is not really an issue.

But assuming I do need to add the OSB, what's the best way to fasten it to the existing subfloor? I imagine I should use screws instead of nails, but do I also need to use glue?

Thank you!

  • I'm curious why you took out the particle board. It added some stiffness, which is mostly what you need to replace. – isherwood Mar 9 '16 at 17:54
  • I removed the particle board because it will not hold the nails from the flooring I'm installing. If you were doing a floating or laminate floor, the particle board could stay. – Mack Mar 9 '16 at 19:16
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I'm not an expert, but here is what I found out when I redone my bathroom.

The OSB is used to add stability to the floor. When walking around, if you're only on plywood, the floor will bounce; simply adding the hardwood floor over the plywood sub-floor will not solve that issue.

When installing the OSB, using floor screws is sufficient. No nails, as these will move and you'll end up hearing them. And while you're at it, you should screw the plywood to the joists if it's not already done.

And if you could get tongue and groove OSB, you'd reduce even more the risk of hearing your floor ;)

  • T&G is only available in 3/4", and it's mostly to keep joints from shifting. In this case, the half-inch plywood makes it unnecessary. Good post. – isherwood Mar 9 '16 at 17:57

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