I have a pending inspection report, part of which addresses the replacement of about 2,000 square feet of water damaged subfloor. The sheathing was not run perpendicular to the joist: no problem with that call. The edges of some of the sheets do not rest on framing support: again, no problem with that call. But, 3/4" CDX was used on the entire floor. Is CDX grade plywood
an approved subfloor sheathing? Michigan Residential Building Code 2000 is silent on the issue. Does anyone know of a code reference one way or another on the use of CDX for subfloor.
They want one side sanded T&G here.
CDX does not have the span rate for use on a floor.
The standard in this area would permit the 3/4" CDX as the sub-floor layer with a 5/8" underlayment on top.
One has to be carefull in using the OSB underlayment due the fact that most Manufactures will not install their product on it and Warranty it.
Carpeting is about the only floor material that could be used.
I would suggest that you check with your local AHJ and current Flooring suppliers for their reccommendations.
Marcel 
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Huh, Even 3/4 CDX???
3/4" plywood for sub-floor should be tongue and grooved and be grade stamped sturdy-floor.CDX is a exterior grade, not designed for a sub-floor span.
3/4" CDX square edge could be used for the subfloor only if a T & G underlayment is used on the top.
Some areas will use the T & G sturdie floor 23/32" rated plywood, but nothing else for an underlayment.
http://www.sizes.com/materls/plywood_softwood.htm#Exposure
Marcel
Why would anyone want to put down two sub floors when one 3/4 T&G is enough, just doesn’t make sense especially with the cost of sheet good these days, for that matter you could install 3/ advantech sub floors cheaper that two sub floors and it has I think a 50 warranty, If I’m missing something here please fill me in, Thanks
No CDX for subfloors? Then what other plywood can you use? …ACX? That would be a waste. …I must be misinterperating the post and the replies.
Correct me if I am wrong, but CDX is the most common “plywood” used for sub floors, and the sub structural elements (joists sizing and spacing) will determine the thickness required as per the design professionals specifications. CDX plywood is commonly used, and in my opinion a better choice than oriented strand board.
Installation of an ACX underlayment over the sub floor will provide a nice smooth surface necessary for installation of a vinyl floor covering.
Hi. Peter;
I am not talking about two subfloors, I am saying that an adequate underlayment could be installed over a CDX plywood.
In today’s World of flooring Manufacturers Specifications for installations, I would reccommend adhering to their requirements, because they pretty well dictate what they want for underlayments.
As you might already know, OSB is not approved for an underlayment for VCT and Linoleum products, and have to install another underlayment. Now, as you can see, you have a sub-floor of 3/4" Advantec Sturdie floor and have to install a different underlayment for the floor finish selected.
Years ago, it was customary to have to layers on your floor framing system. 3/4" t&g boards at a diagonal and plywood underlayment of various thicknesses.
Check with Floor Finish Manufacturers, the one layer sub-floor/underlayment that was installed might not be adequate for floor finishes.
Marcel 
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Hi Marcel, I get your point now, and your right that some finished floors do need an additional sub floor such as tile or lino. Other than that, standard practice for me is 3/4 Advantec T&G sub floor glued to the floor joists and fastened with 8 penny ring shank gun nails, this application is OK for carpet with pad, hardwood with rosin paper or wood laminate floating on foam, tile and lino needs additional sub flooring either 3/8 plywood or cement board. This said, these applications will effect floor to window sill heights, door openings and floor to ceiling heights required by code. Interesting topic especially when discussing inspections on home that have been remodeled.
PS to my post. Do they even make CDX T&G plywood for sub floors? I don’t think so and any new construction today should be T&G. As Marcel pointed out years ago 3/4 pine sub floors were installed diagonal for floor strength
Typical 3/4" t&G subflooring in California and Colorado is CDX. That’s "C’ on one side, “D” on the other and “X” for “exterior” rated glue. Unless it’s a custom home in which they might call out for improved surface finish on one side for a finish such as vinyl that would show up imperfections… what else would anyone use? Not particle board. Not anywhere with land prices the way they are. Well, OK. Elko, Nevada remodel.
The “X” grade relates to the glue type, not the span rating. Plywood is not graded to meet allowable spans, it’s rated by percentage of voids, wood species, number and thickness of veneers and type of glue… engineers call out a certain grade and thickness of plywood depending on the design requirements.
For the simplest answer to your question, ask any local framing contractor.
Go to www.huberwood.com enter key word advantech. I have been using this on my projects for quite awhile and now use the 5/8 for roof sheathing, it’s more money than plywood but water will not effect it during construction, comes with a 50 year warranty and it’s more stable than plywood.
Hi. Peter; Right on.
Advantech is manufacture right here in Easton, Maine. 220 mile from here North or 45 miles South of my home town.
Takes a while to get my point across and it su$cks to be French sometimes, but I manage. ha. ha.
Marcel
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That’s not your fault Marcel, I didn’t think about finished floors like lino and tile, by the way does it seem strange that no one is posting about Advantech from other parts of the country? I thought it was pretty much a standard for today’s buildings
Different strokes for different folks, I guess.
Marcel
Hey Kenton, why is it labeled on 1 side C and the other D??? Please more info
You stated… Typical 3/4" t&G subflooring in California and Colorado is CDX. That’s "C’ on one side, “D” on the other and “X” for “exterior”
What Kenton is refering to the grading system for plywood veneers. Outer veneers are graded with A, B, C, or D.
A is a smooth grade veneer without voids, knots, and plugs. Often used in applications like floor underlayment for vinyl (not subfloors) and maybe some cabinets.
B (never seen it , but is is a grade down from A)
C Voids are plugged, not sanded
D Voids are not plugged, rough
That is a real basic description and more could be added.
Now when you see “CDX” stamped on the plywood, it means that there is C grade veneer on one side, and D grade veneer on the other visible side. The X just indicates that the glue is weather resistive.
They make ACX that performs well for underlayments.
If plywood is used in Washington it would be TNG CDX like Kenton described. However there are alot of builders that use “oriented strand board” OSB panels and these are manufactured under various propietary names.
We see alot of OSB made by Lousiana Pacific (LP), and Advantech that was named in previous posts is also an OSB based product.
I have my own name for the stuff “WasWood”.
I would prefer plywood over the OSB any day, but that is just me.
What Harold said is correct. It just goes to show that different products are used in different parts of the world. For imstance, Pine was never used in western washington, only doug fir. We always use what is available regionally. I think some of the confusion was about terms. Subfloor is the structural part, underlayment is used to give smooth surface or rigidity (tile flooring)