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My house is 24'x24', (2 story), kitchen (main floor) has approx. 5 "bowed-up" floor joists in a row in the middle. I want to change all cabinetry, so while removed, how to "safely" remedy this bowed floor? I have access to the 2"x8" floor joists from unfinished basement. Built in late '78, main beam is wood. Would also like to know what causes this. Can I "sandwich" the bowed floor joists between 2 others (adhesive and bolts), then "shave" the top of the bowed joists in the middle? Seeking advice...

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    Because of the way lumber is graded, reducing the depth of structural members by shaving or ripping or other means is prohibited by most model building codes. In addition, there is inadequate information to determine what size members are required to support the floor based on the information provided. – ben rudgers Nov 17 '14 at 4:29
  • @benrudgers - that is right but you can sister (with same type or greater dimensional lumber) then shave. What we have done to a few old houses in our area. This is one of my least favorite jobs. – DMoore Nov 17 '14 at 21:23
  • Does "bowed-up" mean the joist sagged in the middle? Or could it be that it was held high in the middle and the ends were pushed down? – wallyk Dec 17 '14 at 22:37
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You'll end up getting different answers from different people. Some folks actually will tell you to notch the bottom of the joist to let it sag back down before sistering the joist. But IMHO, it would be best to know the cause and effect before making any permanent structural changes like this.

I had a similar problem (high joists in poorly constructed house, not bowed) and ended up just raising the other joists to be level with the high ones. No structural changes, just shims on top of low joists. Resulting subfloor was dead flat when all was said and done. If your joists are truly bowed up in the middle, it will be more work since you won't be able to use uniform thickness shims. Shims on the outside will have to be thicker than in the middle....

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