When we attempted to replace subflooring over a weak spot in a hallway, we discovered the floor joists underneath were actually the source of weakness. They appear to be the original joists from when the house was built in the 50's, and the ones we can see are almost completely rotted. We're unsure of the reason for the rot.
The trick is that this is on a slab with only about 10 inches between the joists and the slab, with no way to get under it. Is our only option to tear up everything from above and replace the joists? Is there any way to know if other joists have the same problem, without cutting a bunch of holes in the the subfloor?
Any advice or assistance you can provide would be greatly appreciated!