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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.

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Under no circumstances do you want to consider "shaving off" or bottom cutting the joists to try to "fix" this problem. You really need to root cause the reason for the upward bowing of the joists and then aim at correcting that problem. –  Michael Karas May 22 at 3:28

1 Answer 1

Are you really sure that the problem with this doubled joist is not caused by excessive overloading on the cantilevered ends of the overhang joists. From the way that you described it sounds like the ends of the joists that are fastened into the side of the double joist are hanging over the wall foundation. No indication was given as to how far these overhang the foundation but if the ends of these joists were carrying a very heavy load they could be putting upward pressure on this doubled joist causing it to bow up in the center.

Since the doubled joists have little load above them (being as they run under the middle of the room floor) they may very well have bowed up as opposed to the rest of the floor/house having settled as you seem to imply.

If my guess is correct you have two things to investigate.

1) It may be necessary to install a cable truss system on the bowed up double joist to pull it back down in the middle. Then bolt on wider laminated sister beams to hold whole assembly straight.

2) It may be necessary to see if it is possible to remove excess weight on the overhang ends of the joists. If the overhang is an outdoor deck you may need to remove heavy things off the deck or place support posts under the outer edge of the deck. If the overhang is an integral part of the house where a portion of the house bumps out past the foundation by a couple of feet then it may be necessary to jack up the overhang and consider adding additional foundation support under that part of the house.

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I thought about the levering possible as there is a small deck off of the back wall. The final end joist only extends about a foot past the footing with about five feet inside of the footing. To confirm it was not levering I put blocks on either side of the crown and placed a level above the hump. If it was levering the outside (sill side) should have been lower than the inside. When spanning above the crown the floor is level. –  Scott May 22 at 16:49

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