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I'm remodeling the master bathroom of my 1978 split foyer home. I've just ripped out the old shower stall and gotten down to the studs. I was surprised to see that the studs for the common wall with the kitchen are 2x3s. Specifically, there are two walls separated from each other by about 1/2". Here's a picture of what I'm talking about.

shower wall studs

I'm assuming that they didn't use 2x4s because of the need for a bit more space for the plumbing. But, is it normal to use 2x3s and leave a gap? The studs move very easily and I'm worried that they aren't stiff enough for tile.

Is there any advantage to leaving them the way they are or should I put some sister studs to secure the two walls together?

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This is to make room for the plumbing. Not only does it make routing the small pipes easier, 4"+ diameter cast iron plumbing stack pipes are common in old houses and you cannot fit those in a 2x4 wall. Sound insulation might be a benefit but I kind of doubt it was the main concern.

What do you mean they move very easily? Do you mean the 2x3's themselves flex or that they're not attached to the plates very well? They shouldn't flex very much and they should be held firmly in place. Shouldn't harm anything to attach the pairs together to make things more solid. For such close spacing, I would cut 5-6" wide strips of 3/4" plywood and attach them along the doubled up studs with screws where they won't get in the way of plumbing. If they're not attached firmly, you could get some angle brackets and reinforce the toe-nailing.

Wallboard will add some rigidity to the wall, that's true, but it's not structural. If you feel like the studs themselves flex, I think it's worth the minor effort of adding those strips of plywood. If nothing else it will make you sleep easier. Tile can be so finicky it's not worth the risk.

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  • Half inch thick plywood or OSB strips would work just as well for bridging the two adjacent 2x3 studs together.
    – Michael Karas
    Sep 21, 2023 at 2:43
  • @MichaelKaras Probably. But it's not that much material so I'd spend the extra $20 (if that) on a sheet of the thicker plywood. Sep 21, 2023 at 2:46
  • The studs are fixed to the plates just fine. Its just that without any wallboard on them, it is very easy to flex the middle of the studs. I suspect that adding hardiboard or kerdi board will be enough to stiffen it up for the tile. I'll probably still tie them together with some OSB or other material as suggested. I'm planning on some nice tile work and I'm going to take the time to make sure the studs are all in plane. So the extra effort to prevent any flex is probably worth my time. Sep 21, 2023 at 12:11
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    @danielshiplett Kerdi board is made of foam. Definitely wouldn't count on that for wall stiffness. Personally, I wouldn't count on hardi-board either but it's your wall. I'd suggest gluing and screwing whatever sheet good strips you use to reinforce the studs. Sep 21, 2023 at 13:25
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It's possible (if all studs on the common wall are done this way) that they were set up this way for noise isolation between your bathroom and kitchen. Having a break between walls will isolate sound from being transmitted through the walls quite a bit. Add in some typical fiberglass insulation to fill that cavity, and that will also reduce sound transmission.

You'll need to put a solid backer board on there to hold tile anyway, and that should provide sufficient rigidity to hold your tile.

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    Rockwool is a better choice for sound isolation than fiberglass.
    – Ecnerwal
    Sep 21, 2023 at 11:22
  • I doubt it was for sound isolation. The wall didn't have any insulation or rockwool in it. And the bathroom in the next room doesn't either judging by the noise levels we hear in the kitchen when someone is using it. Sep 21, 2023 at 12:07

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