1910 duplex home with center 6" x 7 3/4" beam carrying 2 x 7 3/4" x 16' joists
House framing is not platform, balloon framing. Post and beam with 2" x 12" planks supporting a 4" x 7 3/4" ledger/rim joist between floors.
Aside from 2"x2" cleats studded on interior walls for lathe the planks are carrying load of outside walls. It's gutted and being platform framed but I'm now considering using 2x6 studs under 4" wide rim beam that receives all the joists. This will give me 1 1/2" to rest new sistered 2x12s along exterior wall but I'd need to buildup filler top plates below the 4" beam to fit the 2x12s. The center opposite wall I was thinking of just framing a second wall next to existing to accept 2x 12s.
My concern is the 4" rim beam with a 2x6 (1 1/2x5 1/4) studs underneath will force me to leave a 1/2" space between these studs and exterior sheathing 2x12 (planks) if I'm to get that 1 1/2" support for joists ontop of stud wall