The tile is the stuff that needs the THICKER subfloor. Is the tile in good shape? Did you see cracking of grout lines or popping tiles? These are all signs a subfloor is moving too much for the tile to remain properly bonded to the substrate.

Wood is more forgiving - especially if you are running the wood PERPENDICULAR to the joists. So long as the wood is running perp. to the joists you *should be fine. A thicker subfloor is nice, but may not be necessary. You have the joy of having plywood (not OSB) as you substrate. It is probably doing all the work needed. What is the flooring on the rest of the level? Is it carpet?

When it comes to OSB, you can have great OSB and you can have sh!tty OSB. For that reason I like the safe option of using plywood (although some call this overkill, I like plywood's ability to grab nails/cleats/staples etc). It is also very easy to GLUE to. Some OSB products are TOUGH to get glue to grab on to. And a wide plank oak (anything 4" or wider) will require glue assist (glued down to subfloor) as well as mechanical fixtures (nails/staples/cleats).

Once you are down to the 1/2" plywood, are there any floor height-changes that you need to be aware of? How about door clearance (internal and external doors)? So long as you have all the clearance you need, the plywood is a nice option throughout the home. The cost of plywood for the whole home may be part of the whole decision. A nice plywood runs about $1/sf. Installation is another $1 - $2/sf for labour.

With glue-assisted installs (or any permanent floor in general) it is nice to have a layer of subfloor. That way if future removal of the glued down product is needed, it is easier to detach the top layer of plywood from the bottom layer of plywood. It means the demolition does NOT get down to the joists (that's tough to work around....12" wide HOLES between the joists with nothing but 'air' between you and the ground below).

Thanks for all the great feedback. Here is some additional information: The existing flooring in the kitchen and foyer is ceramic tile and the layers below that appear to be ½” plywood, some other layer, old linoleum, ¼” plywood, and ceramic tile on top. The existing flooring in the adjacent rooms is the standard 2.25 wide oak flooring, run perpendicular to the joists with ½” plywood as a sub-base.

1/2“ plywood sub-base seems pretty standard in older homes (ours was built in 1976).

The ceramic tile has held up well (no cracks) and the hardwood does “ok”, minimal squeaks.

Basically looking to take advantage of the full-gut opportunity to beef-up the sub-floor and bring it more into modern specs. Also, may go back to tile in the kitchen at some point (I’m skeptical of this hardwood in the kitchen trend) and having the sub-base already ready for tile would be helpful. Transitions at doorways should not be too hard to adjust. Just wondering if there is another option that I may be missing.

Hi Andrew. Sounds like others have just proceeded down the 'band aid route' already. If it were me, I would be stripping out ALL the old plywood/layers and re-doing it completely at the joists so that you have the chance to pack and level throughout with a sound sub floor and proper fixings. That would enable a thicker and stiffer sub floor.

A 1/2" plywood over 16 inches is also on the light side as a sub floor. I would be using (at a minimum) 5/8" and eliminating future issues. Regarding the future use of tiles, you could remove the timber in that area and simply lay cement sheet over the sub floor then lay the tiles over that.

Cheers

I would agree with Two's. If, the subfloor is not flat, remove all of it down to the joists. It is easier to level from the joist. If, it is flat and acceptable, just glue and screw 1/2" cdx perpendicular or at 45 degree angle.

Using CDX plywood will help you avoid having to do any additional sanding for a glue assist installation. If, you use a hi-performance OSB, sanding is required to remove the mfg's coating. Adhesives will not permanently bond to it, especially polyurethane base adhesives.