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We are remodeling a second-floor bathroom. The floor dips, and my plan was to sister the joists to level the floor.

This is an old house, built in 1920. The previous owner redid the kitchen. The bathroom we are remodeling is above the kitchen.

I started pulling out the tub last weekend, allowing me to see into the floor and I noticed that the joists are already sistered , presumably to level the ceiling of the kitchen below. So I'm not sure whether I can even level the floor via sistering.

Should I get/cut narrower boards and rest them on top of the existing sisters or sister again on the other side of the joists? Or is there something entirely different I should do to level the floor?

Supplement

Given questions in the comments about why there's such a severe dip, I am attaching a photo of a sistered joist under the kitchen floor showing a split joist, which I assume is the same reason the bathroom floor has a 1-2" dip.

sistered old joist with split

Also, I tipped the old tub on its side, which allowed me to share pics of these joists:

sistered joists 1 sistered joists 2

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    Having never been in your situation, my instinct would be to add new, level joists on the other side and rejoice in the flat floor & ceiling and incredibly stiff floor, resting assured that this particular piece of your house is very unlikely to collapse any time soon! However, as neither a professional carpenter or engineer, I'll leave this as a comment, not an answer, because I'm not certain that this is the best approach. – FreeMan Sep 25 '20 at 11:17
  • There's plenty of other ways to level a bathroom floor. what is your scope of work and intended floor finish? – Jasen Sep 25 '20 at 11:33
  • We're near end of demo down to the studs. We want to tile the floor. It previously had laminate on top of linoleum. I'm aware of leveling compound, but this is too much of a dip for that. It's maybe and inch or 2 lower in the middle than the edges. The top of the closet door is at a noticeable angle from the settling. – hepcat72 Sep 25 '20 at 11:51
  • The bathroom is roughly 8'x8'. – hepcat72 Sep 25 '20 at 11:58
  • Do you know why it's sagging so much? A 1-2" drop from the wall to the center of an 8x8 room is quite severe. – jwh20 Sep 25 '20 at 13:13
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There should be no reason you cannot sister the other side with new material. You could use 2X6s to get enough surface for good attachment, notching a little here and there to get around wires and such. If the original joists are clean enough, construction adhesive can be used to minimize the need for so many fasteners.

Yes you can rip material to add to the top of the joists too, it is a little more tricky to a degree. glue and screw it in place too. the cut may need to be curved a bit yo accomodate th bow of the original joists. A circular saw will have no problem doing a slight curve.

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  • Ok, great. That's reassuring. From what I saw under the tub, the space above the existing sister is roughly 4". Maybe 3. (Perhaps the previous owner didn't use a really broad sister, as in the basement, because he was only leveling a ceiling. My assumption is that those sisters are leveled and the only cut I would need to make to add to the top of it would be straight, not curved. But generally, I think you're right that leveling would be easier if I add a second sister on the other side. – hepcat72 Sep 25 '20 at 14:17

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