Designing Kitchens and Bathrooms - ...a hump in the midddle of the floor...

Good day,

I am in the process of installing ceramic tile in my eat in kitch.

What I thopught to be a simple fix with the sheathing turns out to be a joist that is bowed upward, creating a bouncy hump in the floor.

The floor is 20" oc with 3/4 osb (MH)

I was thinking of loading the floor at the apex and run 2 or 3, 4x"s across 4 or 5 joist and secure tightly, and remove the pressure when I come across with the 19/32 that is goinging down first.

will boxing it in ( about an 8x8 area reachable) help?



thanks J

Moderator note: Removed e-mail address to prevent inbox from filling with SPAM.

Ceramic tile requires a flat subfloor. Some remove subfloor and plane hump out of joist in order to make floor flat. Concrete underlayment over subfloor is recommended before installing ceramic tile.

hauseofboats,

Actually in my thinking this question belongs in the tile forum and not necessarily here, I don't know why one of the on-their-toes-Moderators hasn't moved it but OH-WELL!

Here's what I think.

Your floor joists aren't on 20" centers but technically they are on 19.2" centers which is a typical method. This tells me that you probably don't have dimensional lumber joists but instead your joists are engineered joists.

If this is the case there is the possibility that the joist flanges (tops and bottoms) are in fact made of plywood, in some cases this is how it is done. The 'webs' (middle part) are also then made of either plywood or OSB. At any rate you won't be able to plane the flanges like you could with structural lumber. If in the event the flanges are structural lumber then still - planing them can be very difficult and isn't something everyone could do.

That's the first problem. The next problem is that joist centers of 19.2 inches require a double laminate of subfloor material before tile can be installed. I'm not clear if that is what you are doing when you mention the 19/32. If this is the case the top layer of ply can be square edged but you want to be sure to overlap the joints of the new ply with the old subfloor by a wide margin and then don't nail the new to the joists at all, only nail the new to the old.

I am also not understanding your "boxing" plan but I doubt you will simply relieve the (so-called) pressure on the proud joist that easily.

Let's catch up on terms and get your comments then we can go on if someone else doesn't chime-in with a solution.:) But I'm thinking planing isn't at all a viable solution to the problem.:)

Just out of curiosity, does your house have a cantilevered deck outside the kitchen/dining room? I have run across this many times when the cantilevers are not bolted to the main joisting, only nailed. The weight of the cantilever causes the joist extensions to lift up in the dining room and cause a "hump".

EXCELLENT question chandler, I would have never thought of that but good question.

Engineered joists are by their very nature right on the money every time and to have a crowned joist would be very rare. There is more here than meets the eye I suppose.:)