The original subfloor was very thick - perhaps a full inch. The 3/4 treated ply should be fine. Can I get away with 1/4 inch wonderboard on top of this as a backer for tile?. 1/2 inch may case problems w/commode collar (may be almost flush).
I originally had a tub, which was removed. I'm putting a shower in and am going to build a sturdy platform to give me room to get the plumbing right.. Thanks for the quick reply