Can new tongue-n-groove subfloor be butted up against old non-T&G subfloor? And still maintain structural integrity for tile?
Details:
Remolding bathroom.
Moving toilet, bathtub and shower feeds to new locations so had to open floor.
Old subfloor was solid and never creaked nor tiles ever came loose.
Hate to rip up good subfloor in closets and other areas and risk changing any more structural integrity .
Thinking of sliding groove end of new plywood under wall frame to mate with tongue of existing plywood (under wall frame). Butt side to existing subfloor and in picture.
Best Answer
It looks like it will be well-supported by floor joists, so I would not have a problem doing this. I can't see everything at the bottom of your picture, but it would be important to me to have the corners of your replacement subfloor supported. I've had to add blocking perpendicular to the joists in order to meet this before but it looks like you might have about 3/4" of joist to support the edge of your new plywood and that would be sufficient.
If you can spare some floor depth, I also recommend using a backer board for tile on top of the subfloor (your question doesn't say whether you were considering this or not). You can use the thin stuff (1/4" or 3/8" is enough) the 1/2" stuff is for walls and primarily to match the thickness of drywall. Check out install guides for the backer or concrete boards, I think it says to install with seams perpendicular to your subfloor seam direction.