Fix Bowing in a Floor

Learn what may be causing a bow in a kitchen floor. Learn how to fix the floor by cutting the floor joist and installing a new floor joist.

LESLIE: Claire in Illinois wants to install wood flooring. How can we help you with that project?

CLAIRE: I am getting ready to have installed 3/4-inch prefinished hardwood in my kitchen floor.

TOM: Nice. OK.

CLAIRE: I’m considering the pros and cons of having the flooring in a room where there’s possible moisture from a dishwasher or a leaking refrigerator. There is a big bow – b-o-w – under the linoleum that I currently have under there; a kind of a gradual rise and then it slopes down on both sides. I’m wondering what might have caused that and how I could best repair it.

TOM: Well, if you have a big bow in the floor, it’s probably caused by floor joists that …

LESLIE: Are crowning.

TOM: … have crowned; have bent. Crowning means it’s sort of bent; bent up.

LESLIE: It’s bowing upwards.

TOM: Bowing upwards.

LESLIE: So it’s creating that lift in the floor.

CLAIRE: OK, would that be bent from water?

TOM: No, just sometimes dimensional lumber just that. And it’s very obvious when it’s under a sheet product floor like vinyl.

LESLIE: That’s flexible.

TOM: It will be not nearly as obvious under hardwood floor.

CLAIRE: OK. Somebody did say that in order to correctly lay hardwood floor so you won’t have gaps, that you have to address the bow.

TOM: Well, if that’s the case, the way you address it is as follows. Typically, what you do is you can cut the floor joist in one or two places and what I would do is I drill – when I do this repair, I drill about a one-inch hole about an inch-and-a-half down from the top of the floor joist; I run a reciprocating saw blade and basically cut it right down. So now the joist is cut in half; completely ruining the structural integrity of the floor joist. That will help bring it down to where you need it to be but now you still have the problem of having to reinforce the floor joist.

The way you do that is you add an additional floor joist which is exactly the same length and size and you put it against the one you just cut and you glue it and bolt it together, creating sort of a …

LESLIE: Is that called sistering?

TOM: Yeah, it’s what we call a sister joist.

CLAIRE: S-i-s-t-e-r?

LESLIE: Mm-hmm.

TOM: Yes. So it’s a job that will take a few hours to accomplish but you can level the floor that way.