I have a small rectangular home 33’ x 26’. It’s built on a walled foundation with 2 x 8 joists running the width of the home and a center I-beam support. At the back of the home they stopped the cross ways joists about 5 feet from the end of the foundation. They then doubled the joist and hung joists out 7 feet to the end of the house. The double joist runs under two bedrooms. I now have a 1” hump in the center of each room where the double 2x8 is located that spans about 8 ft and slopes off about 1’-6” to either side . The hump is kind of oval in shape and pushes up into the room reducing the floor to ceiling height. I was planning to jack up the floor but in looking at all of the other parts of the house I think this would do more harm than good. The house has settled very evenly. It’s just that the doubled joist has not settled in the middle like the rest of the joists. Normally I wouldn’t consider shaving the joist. However, since this joist is already doubled and the extra strength seems to be stopping it from behaving like the other joists would it be safe to shave it down about ¾ of an inch at the middle sloping up to each side so as to level the floor and regain the lost inch of ceiling height. In my case the safe route taken by the builder has caused more harm than good.
One last thing, I thought of the traditional method of making a cut at the bottom of the joist waiting for it to sag and then sistering another joist to it but, it's already a double joist and I'm afraid I'd have to cut too deep in both to get them sag.
How about this option? As this now appears to be a crown is it possible to pull the crown down. My thought is hanging steal angles perpendicular to the crowned joist 12 inches either side of the crown. I can through bolt a U channel with a welded carriage bolt above each angle that drops through the angle and over several days pull down the crowned joist. I have a very easy crawl space in which to work.