Is a 1/2" CD plywood subfloor sufficient thickness to nail a 3/4" oak flooring or do you need more than a 1/2" subfloor?

No, it is not enough beef, for a subfloor to nail to.

No... but aside from the thickness part , CDX does not have a T&G and is not a subfloor grade of plywood. Too many voids in the inner plies.

Ok ..... thank you all for the responses.

Jerry,

We use CDX all the time, it does have some voids but I have never seen them cause a problem.

This is what Georgia Pacific says.

Manufactured For Strength
"CDX" Sheathing Plywood
Specially designed for subflooring and wall and roof sheathing, but can also be used for a broad range of other construction and industrial applications. Available in a variety of thicknesses, panels can be manufactured as conventional veneered plywood or as a non-veneered panel. Specify Exposure 1 when long construction delays are anticipated.

Designed for subflooring and roof and wall sheathing.
Long-term dependability for residential and commercial construction.
4' x 8' panels are available in 3/8",15/32", 19/32" and 23/32" thicknesses.
Weather-protected applications only.

Sorry about the double post.

CDX is what I always spec, too. Not to go directly over the joists, you would need a T&G for that, but as an underlayment.

Gary explained Subfloor and underlayment, in the past. I too call underlayment a subfloor, when I forget and go back to the days before I knew there was a difference in terms.

Nofma also refers to plywood on a slab as a subfloor.

PLYWOOD-ON-SLAB SYSTEM.
This system uses 3⁄4" or thicker sheathing grade exterior
plywood as the subfloor over the appropriate vapor retarder.
Loose lay 3⁄4" plywood panels over entire floor. Laying plywood
on a diagonal to the direction of the finished floor will
help prevent cracks associated with panel edges

I know what you are saying Buddy. But CDX is not a subfloor/underlayment combination like AdvanTech or a plywood 3/4 Plywood UL T&G. CDX is used when using a two layered subfloor system. not as a single layer subfloor. It needs to have some type of underlayment installed on top.

On floating slab installs it would be OK because their no span between joist to deal with. I switched over a few years ago to using a BCX underlayment grade plywood because 4-ply 1/2" CDX is getting hard to come by and also because plywood is sorrier now than it was many years ago.

Just me... I am too anal for my own good.

The reason for differentiating between subflooring and underlayments is that we pros often recommend removing particle board underlayments. There are some homes that have particle board subfloors. If the homeowner/DIYer started ripping that out, only to find dirt below, I think that would cause problems. Besides, we need to differentiate between the products. Subfloors and underlayments do perform different functions, although in wood flooring, they may be similar. I've never understood that back east older practice of installing 1/2" CDX and then 5/8" or 3/4" particle board over that. That was never done in CA, at least on any home I've ever seen. Maybe on an older custom home built somewhere. Here, the subfloors must be 5/8" plywood MINIMUM over joists 16" OC. Why would anyone install 1/2" then particle board over that and think they're saving money? Just makes no sense to me.

Builders stopped using that method here in VA about 25 years ago. If you would look close alot of that 1/2" CDX was form plywood used for foundation walls.... you can see the holes drilled through it. They did that because carpet was all the rage.

All you will see here now is 3/4 T&G subfloors, mainly AdvanTech. I have not seen a new construction using 5/8 T&G in about 10 years.

Same here Jerry. We just use the CDX for subfloors on slabs, the carpenters and general contractors are licensed to install the subfloors on joist because it is considered part of the structure. We can do minor repairs only on this type of subfloor.

Ok, that sorta makes sense. Since I guess you have full basements and the plywood would still be full sheets. Here, very few full basements so the cheapo builders used the 2 x 10's and 2 x 12's from the foundation forms as joists. Not uncommon to see some of the joists covered with concrete slurry, even though they're supposed to oil them before a pour. And yeah, most all new raised wood foundation homes with wood subfloors are 3/4" OSB of one brand or another. But I have yet to see one OSB subfloor that was as flat on the seams as GP's Plytanium Sturdi-Floor. OSB always puckers at the seams and always needs sanding.