I am doing a complete gut remodel of my bathroom in a 1962 construction home. The subfloor is 1-5/8" x 7" tongue and groove set on 4 x 6 girders that are spaced 48" OC.
A leaky toilet completely destroyed a section of the subfloor, and caused rot to eat through at least 50% of a 4 x 6 girder. There is no floor sagging, but I imagine the beam needs replacement.
I can't find a match for the T&G planks, and the height makes substituting it with plywood a no go. Since the girders are 48" apart, I can't do plywood anyways, unless I add a bunch of joists.
No idea how to address this.
Removed toilet to reveal rotten subfloor: