u/CostcoBulkBuyer

Trying to make the floor level, Best way to fix the rotting rim joist? It’s kinda in there.

This is a rental property and one of the downstairs tennant moved out. All the floors downstairs are uneven. 24inch on center 2x6 floor joist with bridge like bracing. I’ve ripped out the kitchen cabinets/drywall due to being infested with mouse and cockroaches. and really want to do some subfloor repair work. This fourplex was build in 1983. It’s got cripple wall(from what it looks like) surrounded by dirt. I cut a hole opening in the subfloor and notice that the rim joist(I think that’s the term) is completely rotted (can see on the photo with hammer). How do I replace rotted 2x6? I’m sure there are more sections that needs repair. Can I replace piece by piece?
Do people normally replace the subfloor chunk that sits between the wall and the rim joist or just make the leftover subfloor flushed with the wall leave it there? I’m just trying to make the floor level and make the downstairs floor more solid. Who does this 24inch on center with floor these days?