My little powder room has been such a headache, hoping someone here can shed some lights. Little background of the house, built in 1909 on post and beam foundation with perimeter of the house sits on linear( continuous footing) sometime 1920-30’s or earlier, then owner built 3ft x 23ft bump out that has cinderblock footing 2ft away from the original perimeter footing with 1ft cantilever.
When I opened the 3/4” thick solid diagonal subfloor, I see that the added joist are only 3ft and looks like there weren’t an adequate fastener attached at the beginning of 3ft added joists. Because the powder room is about 6ft parallel to the joist, where added joist beginning is the highest point and each ends of the room is sloping down by 1/2” to 1”, planning on adding plywood to install tile, this current waviness is no go unless I address this issue, I’m willing to add 8ft added joist on the area to give itself enough back span so the tile deflection is high enough, this means also raise the beam, I was hoping if I can just add longer joist and add shims on top of the joist so I don’t have to take recent earthquake Retrofit work done by a professional foundation company( has plywood up against to sill and post). Or any suggestion on how to go about? Thank you!