I am finishing a project started by someone else so I don't know the logic behind material selection. It's a second floor Accessory Dwelling Unit stripped down to the 3/4 plywood subfloor except for where a few new sheets of 23/32 tongue and groove plywood were laid, floating on the subfloor. Before I continue what was started I want to make sure that laying such thick plywood for underlayment is okay, not adding too much weight and if so should it be secured or left floating? It seems excessive to me and will defiantly lead to me having to reframe doors and such.

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    – isherwood
    Sep 28, 2023 at 20:47
  • 1
    By "floating" I assume you mean it's just laying there unfastened. There's no reason to put something like that in permanently. Are you sure it's not there to temporarily cover up whatever's underneath it like bad subfloor? Or just hadn't gotten around to fastening it down? Sep 28, 2023 at 20:49
  • Pull a sheet up, or is it glued and screwed? Then maybe just under cut the doors some more. Which if there's no HVAC returns, need to be anyway.
    – Mazura
    Sep 29, 2023 at 7:02
  • Thank you all for the input, I tried looking up building codes for the answer but in this case I couldn't quite understand the terms used. I called it floating just because it's not been secured to the original subfloor, your guess is as good as mine whether that was intentional or not. I see a couple spots where the second layer of plywood hadn't been laid where the subfloor was cutout and replaced, poorly executed. Sep 29, 2023 at 14:46
  • IIUC, you've got 3/4" (24/32") plywood subfloor, then somebody left a few sheets of 3/4" (23/32") plywood laying about ("floating") on top of it and you're wondering if it's OK to clean up the mess? Your description of a "few new sheets" implies to me that they're just laying there, even if the T&G have been pushed together and the fact that they're "floating" (not fastened) means you can move them at will. I'd definitely recommend moving them to see what's underneath!
    – FreeMan
    Sep 29, 2023 at 15:14

1 Answer 1


1½" is not at all too much. It's about ideal, actually, if you have the space available for it. Ceramic tile requires nearly that much, at a minimum.

Your followup question has been well addressed already:

When installing two layers of subfloor, is it okay to secure both layers to joists?

Proper way to install double-layer of subfloor?

Plywood underlayment over plywood subfloor - how to secure

How best to join 2 layers of sub floor?

What is the proper way to add another subfloor layer?

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