I am replacing a 1920? freestanding claw foot tub with a new TOTO cast iron tub with apron. I believe the weight of the new tub is about the same as the old claw foot tub. The subfloor is 3/4" thick 3-1/4" width tongue and groove 100 year old redwood. After removing the layers of vinyl and linoleum the subfloor appears to be in good condition. The framing is 16" OC. I need to shim the new tub about 1/2" on 1 side to level it.
Do I need to put a piece of structural plywood above the existing subfloor? I will be tiling and using cement board as the under layment for the tile. I don't want too much of a step at the transition from the hallway. thanks.