I am looking for some information or suggestions for a problem discovered recently. I built my house about 4 years ago and although I was the General Contractor, I had the framing done through a sub contractor. I poured 9 ft. basement walls and built a 1 ft. 2x6 knee wall that I set the joists on. This gave me a 10ft. basement ceiling height. Anyway, I noticed that the knee wall parallel to the floor joist (the one the long rim-joist sits on) is out of plumb about 1/2 inch in 12 inches. This is a pretty significant lean. Oddly enough, my rim-joist is plumb and all of my mechanicals are still tight to the top of the knee wall. This gives me the indication that this happened during construction and has not moved since. I did notice that there is not any bridging in between the last joist and the rim-joist. I am not a framer, but I have an understanding of the basics. Before I consult a structural engineer, I would be interested in some feedback. How much weight is on a rim-joist? Could it have just been the weight of the walls above that caused the knee wall to move? The exterior walls are 2x4 and the knee wall is 2x6 with the rim-joist sitting on the outside of the wall. What about adding another rim-joist inside of the original one? Any suggestions?