I'm trying to plan the repair. Assuming I treat/kill and the rot and stop the water ingress are these solutions sound structural fixes(joists are 5" x 2"):
Cutting back the rotten joists, a metre or so back from the rot. The I bolt on new timber on one side and sit them in a widened hole in the wall. New timber will be treated of course. If this method is sound just how far alongside the existing joist do I need to run the new timber?
Again cutting back the same amount, this time fixing a new piece into the original wall hole and sandwiching it to the old timber.
There's also enough room in the cavity to leave acro props permanently in place. Any advice much appreciated.