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Old 12-19-2010, 03:15 PM   #1
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One Joist Too High

I'm adding a bathroom into my bedroom and removed the hardwood flooring and T&G sub-floor. I am ready to install a 3/4" plywood sub-floor to replace the old T&G, but the joist closest to the outside wall is between 1/8" and 1/4" higher than all the other joists, which is causing the sub-floor to bow.

The house is 80 years old so the joists are 2x6" oak. The hardwood makes it very difficult to plane down, and because the joist is butted right up against the outside wall, I can't use a power planer.

There is already a pretty nasty slope in the floor (before figuring in the problem joist), so I can't shim up the joists or add sister joists without creating either an intolerable slope or major difference in height between the new floor and existing floor.

The best I can think of is to try to cut a 1/4" of thickness off the last few inches of my plywood sub-floor so that it rests on all the joists (see picture). I'm still left with a floor that is not level, but at least it will be flat.

Does anyone have any suggestions of how I might do this? I was thinking I could run the edge of the plywood across my table saw, but it would take a good 20 passes to thin out 2.5" of the plywood like I would need. I'll have to cut across the grain, so I don't think using a planer would work. Thanks for your suggestions!
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Old 12-19-2010, 04:01 PM   #2
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I suggest that you sister on a 2x4 or 2x6 at the correct height ---if you you are adding a tile backer board on top---I think you will be safe stopping the 3/4 subfloor at the high joist and filling the void with thinset as you set your backer board.


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Old 12-22-2010, 08:53 PM   #3
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Sounds like the wall is in the way of the power planer. Could you use your circular saw and rip guide to rip the top of the last joist from the side?
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Old 12-24-2010, 05:44 PM   #4
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i would do exactly as oh mike suggests.
just screw on a 2X4 at the height you want on that last joist. stop the subfloor as soon as it bumps into problem joist. then run your finished floor over that last joist. no one will ever step on it.
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Old 12-24-2010, 09:07 PM   #5
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wouldn't shims be more structurally stable? sandwiching in 1/8" or 1/4" strips seems like it would be a stronger method than relying on fasteners with the sistering method
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Old 12-24-2010, 09:18 PM   #6
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Yeah I would sister the joists or do like CplDevilDog suggests if you have room between the joists.
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Old 12-30-2010, 04:09 AM   #7
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I agree with Schmolze. Tight to the wall and with a 2x4 supporting the hanging end of subfloor (glued and screwed) should be A OK


CplDevilDog is offline   Reply With Quote

sub floor slope , sub floor thickness , unlevel

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