Originally Posted by nealtw
The 3/4" plywood subfloor runs under the wall, infact all the floor was laid for the whole condo and then the walls were built. The peice that you removed is a previous repair. The distance from center to center on the fuull height joists should be 16". the other structure below was likely for something in the ceiling below and the addition to that should not be there as that is not part of the floor structure. On new structures all the floor plywood is tongue and grove so that the floor moves as one and a repair like you have would have a block of 2x4 screwed under the joint between the joists. If yoiu do not have tongue and grove you may need something more added or thicker backing board, not sure. See if you can see insulation around the tub drain, it may have been left out during the last repair job.
Ah, good to know, I've never seen that before. Not surprising, with my limited experience with carpentry
The distance between the two full height joists is around 23", is that odd? I didn't see any tongues or grooves in the plywood flooring. I didn't see insulation around the tub drain.