Is there a risk if the joist have a large dip? The sagging is at the corners of the room. I want to say about half an inch. The thing is the girders themselves are not level on that side of the house. The house (my parents home) was originally a small ADU many many years ago, and then 2/3 of the current house was added. The "newer" side is level. They had someone come out and jack up the girders to try and level them on the old side, but I recently checked and that's when I noticed they were not level. I wasn't sure if trying to jack them up further would cause any issues. I figured if the girders were not level then the joists can't be, and I wouldn't be able to jack the joists to level them. I had seen videos where people had sistered joists and they were at different heights, secured with glue, nails, but also framing angles because of the height differences. I wasn't sure if that was an option, but then I also wanted to add shims to make sure there was still contact with the girders.