Venting a basement bathtub

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Girafdaniels

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The last element to plumb in my basement bath/laundry remodel is the bathtub drain. Like pretty much everything else, it was done poorly (or outright incorrectly!) when the house was built.

The photo shows the plumbing that I’ve done in the hole that was already there. It wasn’t vented originally, so the bathtub always drained quite slowly (which didn’t really bother us). I also never heard gurgling or smelled gases with that previous set up, so I just went back to it (because I don’t have wall space to run a vent up and the slab precludes options elsewhere). FYI, the wall space to the right has an I-beam at ceiling height, so I couldn’t get a vent up that way (without an awkward frame out that’d look really stupid).

So, I thought I might try to squeeze a studor vent off the trap arm where it’s exposed and run it to the wall and up around 16” with a louvred access into the adjacent room. Proposed line pictured in red. Any reason that wouldn’t work? I’d really like to do nothing (!), but I’m guessing the studor vent would be my best (and really only) option.

That san tee pictured isn’t glued up. Once I’ve got it connected to the rest of the waste/overflow set (and that’s all attached to the tub), I’m anticipating having to reach through that hole in the drywall and glue it down to my drain pipe when I’m doing the final tub placement. Not looking forward to that either!

Thanks in advance for the help!
 
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Girafdaniels

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Any advice? Really appreciate any hard-earned insights and the time it takes to share them.
 
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wwhitney

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Are you sure the tub drain is not wet vented downstream?

Looks like the drain coming out from under the slab is 2", while the new work is 1-1/2"? If so, it would be good to vent the 1-1/2" portion before the size increase, I believe you're not supposed to change size in the middle of the trap arm.

I believe your proposed venting is compliant with the IPC.

Barring obstructions on the reverse, you might as well enlarge your drywall hole to run from center of stud to center of stud, and a bit taller won't make it any harder to patch.

In theory if your pipe assembly is perfect, you could glue up everything, drop the tub in on top of the gaskets, and insert the drain strainer and overflow from inside the tub. In practice that sounds really hard, and I've never dealt with a tub on a slab. If it would make things easier, it'd be fine to use a 1.5" shield coupling for the final connection.

Cheers, Wayne
 

Girafdaniels

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Are you sure the tub drain is not wet vented downstream?

Looks like the drain coming out from under the slab is 2", while the new work is 1-1/2"? If so, it would be good to vent the 1-1/2" portion before the size increase, I believe you're not supposed to change size in the middle of the trap arm.

I believe your proposed venting is compliant with the IPC.

Barring obstructions on the reverse, you might as well enlarge your drywall hole to run from center of stud to center of stud, and a bit taller won't make it any harder to patch.

In theory if your pipe assembly is perfect, you could glue up everything, drop the tub in on top of the gaskets, and insert the drain strainer and overflow from inside the tub. In practice that sounds really hard, and I've never dealt with a tub on a slab. If it would make things easier, it'd be fine to use a 1.5" shield coupling for the final connection.

Cheers, Wayne

Wayne, thanks for your continued advice and support!

It’s possible (?) that the tub is wet vented with the toilet vent I just added. I’m not sure if the set up here with that vent location upstream from the wye into the 3” line qualifies. And even if it does, which would be great, It’s roughly 8’ away from my tub’s p trap. That being said, I’m almost positive that there isn’t a full 1/4” fall per foot on the tub’s 2” drain leading to that wye (because the wye, if I recall right before pouring concrete there, wasn’t 2” down from the bottom of the slab there).

So, maybe that would work if I switched out all my 1 1/2” work for 2”, and then reduced it back to 1 1/2” above the trap to connect to the waste/overflow?

I can definitely open up the drywall more there. I’ll need as much space (and precision) as I can muster!
 

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wwhitney

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You can't run a dry vent for the bathtub up the wall with the drywall cutout, over the door way, and connect up to the toilet vent? That would be the best solution.

I don't believe a dry vented toilet can wet vent a bathtub. If your new vent connected to the bathtub trap arm within the proper distance and dry vented it instead of the toilet, that could have wet vented the toilet. But that ship has sailed.

So assuming you don't want to break up any more concrete to address the bathtub fixture drain slope concern you have, I suggest just venting the bathtub, either revent to the toilet vent or with an AAV.

Cheers, Wayne
 

Girafdaniels

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I could actually run it up that wall and over the door, Wayne! I’ll have to redo the cold supply and move a couple other things, but I’d rather do all that now than have a problem (or potentially noisy studor valve access in the living area) later.

Back to DWV work! Thanks for the advice again.
 

wwhitney

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Is it a load bearing wall? If yes or if unsure, post a picture from plate to plate, including any exposed joists above.

(Speaking of which, those bottom plates all appear untreated, is there is a sill sealer or other barrier between them and the concrete? You chopped out a section for the toilet vent, so it should be obvious.)

Cheers, Wayne
 

Girafdaniels

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Is it a load bearing wall? If yes or if unsure, post a picture from plate to plate, including any exposed joists above.

(Speaking of which, those bottom plates all appear untreated, is there is a sill sealer or other barrier between them and the concrete? You chopped out a section for the toilet vent, so it should be obvious.)

Cheers, Wayne

Not a load bearing wall.

And, you’ve got a discerning eye. Those bottom plates are not treated. The whole basement was built that way. I’ve put down treated anywhere I’ve done new work, but haven’t bothered with it otherwise. Wouldn’t be worth it in this house!
 

wwhitney

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OK. I still suggest stud shoes where you take your pipe through the studs. If it's an area where you are going to tile, it's worth flattening the studs, which probably means recessing the shoe into the stud 1/16" or so.

Cheers, Wayne
 
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