Is 3/4" AC Plywood on 16" joists suitable for subfloor?

I am remodeling and the original subfloor is 3/4" plywood (not tongue and groove) and I want to match up with this, AC (6 ply) is all I could find. On top of this will go tile underlayment and then tile.

It seems modern building has gone to 23/32" tongue and groove plywood or OSB

  • 1
    Look at the stamp on the ply and it should have all the info you need for applications. 23/32 is the end result of "undersized" 3/4 ply (tolerances, they lied - funny how it was always under, never over - not a tolerance issue, but they sold that size as 3/4 for years.)
    – Ecnerwal
    Commented Mar 1, 2017 at 0:47

1 Answer 1


Yes, but over-kill for 2 reasons: 1) 5/8" C-D plywood is fine for 16" on center supports. If you look at the grade stamp on the plywood, you'll see "48/24". This indicates it's suitable for spacings up to 48" on roofs and 24" on floors. You can use 5/8 with a grade stamp of 24/16. Yes, the industry has gone to T&G because builders are using the minimum thickness and the plywood will flex and rub edge-to-edge. This causes noise (and sometimes squeaks). The 3/4" plywood will be so stiff it won't flex and won't squeak. (However, glue and nail it down anyway.) And 2) The A-C designation indicates the A side is patched so it's smooth (and maybe even touch-sanded.) This is used as an underlayment, where the finish floor is to be installed directly to it. (Most vinyls can't be installed on particleboard in wet locations.) C-D is cheaper and doesn't matter in your case, because you're adding an underlayment for the "finish flooring."

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