I just purchased a ranch house (with basement and garage underneath) and decided to try to renovate the bathroom. The flooring was linoleum, after taking off the linoleum, I discovered that the subflooring was a patchwork job consisting of different subfloor heights overlapped, mortar a couple of inches thick (assuming some kind of leveling compound to account for the different subfloor heights), and old tile on just half of the floor... A few areas of subfloor were spongy and damaged.
I got a bit ahead of myself trying to get rid of this subfloor and ended up cutting the subfloor out of the room up to the walls. It was at this point that I realized that the doorway wall isn't supported by any joists and runs parallel in between two joists. Now that the old 3/8" subfloor integrity is compromised from cutting it, it got me thinking that all of the walls in the room have this old 3/8" subflooring between the bottom wall plate and the joists, and I'm wondering if I just seriously affected the integrity of these walls since all of that subflooring is now cut and not supported across joists as it used to be? It seems like the remnants of the 3/8" old subflooring are just sort of hanging unsupported now around the perimeter - especially on the walls that run parallel to the joists.
Is there a proper protocol for blocking around the perimeter of the room for the new subfloor? What about something to keep the old subfloor around the outside perimeter of the room from sagging?
Do I just make 2x4 boxes and cross braces around the inside perimeter of the room and fasten the new subfloor to that and not worry about the old subflooring around the outside perimeter? Or do I put bracing on both the outside and inside of the room? Confused about the proper protocol here.
I am trying to replace the subflooring in the bathroom with 3/4" tongue and groove plywood.
Here are some images: https://i.stack.imgur.com/You5X.jpg