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Old 10-31-2010, 10:12 AM   #1
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Sistering Joists for New Subfloor


My husband and I currently have a gutted kitchen. We are down to wall studs and exposed floor joists - thanks to mold remediation. Our house is 50yrs old. There are 3 floor joists that are not leveled with all the others. On one end, they support the exterior wall. On the other end, they are attached to the basement stairs. The end at the basement stairs is not leveled by about 1/4 inch with all the other floor joists. We have attached metal brackets to add support to the original joist. Now, we're planning on sistering the joist but raising the sister joist by 1/4 inch to make up for the imbalance.

The original joists are 2x9 (?) and are about 11feet long. We're thinking about adding 2x6 boards to sister them, using construction glue, bolts, then screws. However, we're not going full length, just short. Please see pictures below. ANY advice would be helpful...remember, you're not just giving construction advice, you're also saving a marriage.

Are we anywhere near being on the right track??

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Old 11-01-2010, 12:58 AM   #2
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Sistering Joists for New Subfloor


Why is it off 1/4"? Is the header for the stairs sagging, or was it just framed 1/4" off 50 years ago?

I did something similar in my kitchen because my floor joists across a 14' span had started sagging, except I used 2x10 (actual height is 9 1/4") lumber to sister with the existing floor joists. By using a floor jack we brought everything back up to near level and then nailed it all together with a ton of PL adhesive. I have seen what you plan done also, but with 2x4s since the original 2x10 still carries the weight. The reason I went with 2x10s is I was trying to stop the sagging all together, by doubling them up. If your floor has only sagged 1/4" in 50 years it doesn't sound like you have too much of a problem and what you're thinking should work.

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Old 11-06-2010, 08:50 AM   #3
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Sistering Joists for New Subfloor


Thanks, Mr. Louie! It's helpful to know that we're not completely off the mark.
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Old 11-06-2010, 08:59 AM   #4
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Sistering Joists for New Subfloor


If you are low by only 1/4 inch, you may consider just adding a 1/4 inch thick wood shim. Doesn't seem like your joists are sagging, so this does not sound like a structural issue, simply a cosmetic one, i.e. you want a flat floor. You only need to sister joists if you have a structural problem such as a bouncy floor, too much sag, you have added load, or similar.
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