Venting a basement shower remodel

[Oldtimm]

Hello all,

In the process of a remodel and I'm trying to wrap my head around how to vent the shower. The way I see it, I have two options based on where everything needs to be.

Option A (red lines are my proposed runs):

Option B:

The shower trap will be too close to the wall to fork off of it and go up the wall directly behind the trap.

My concern with option A is that the vent for the shower will need to be run horizontally for about a foot before it can turn up into the wall. That said, as you can see, the previous plumbing was more or less done this way as well (there used to be a plumbing wall here that enclosed the two existing ABS vents).

My concern with option B is that I would really, really like to not have to run 2" pipe all the way around the bathroom through 2x4 studs (there's HVAC in the way of just tying into the existing main vent pipe that goes through the roof, so basically need to run all the vent work clockwise around the room to get it where it needs to go, including through the inside frame corner as shown in the top center of the photos - thankfully these walls are not load-bearing). Is plumbing 2" pipe for the wet vent and then adapting it down to 1.5" once the vent becomes dry a legal option?

Are either of these to code? For that matter, is the existing installation to code?

Thank you all!

 

[wwhitney]

Option B is a fine UPC wet vent. The dry portion of the shower vent path can be 1.5", only the wet portion needs to be 2".

Option A has a horizontal dry vent below the fixture flood rim, so it would only be allowed where "structural conditions" preclude keeping the vent vertical (at least 45 degrees above horizontal). The vent takeoff would still need to be vertical (a wye rolled up at least 45 degrees above horizontal), and the vent below the fixture flood rim would need to plumbed like a drain (i.e. LT90 where the vent turns up into the wall). However, since Option B is available, I would think that the exception for "structural conditions" would not apply.

Option A2 is to point your shower trap outlet towards the vent wall (either at a 90 or a 45 or parallel to it, depending on how close the u-bend gets it and how much space you have along the vent wall), turn the trap arm (if necessary) to run parallel to the wall but just outside the footprint, and use a wye rolled 45 to dry vent the shower trap arm (now it should be close enough for the vent to get under the wall before rising out of the slab, and then you use a 60 degree bend to turn the vent vertical). Then you need a LT90 to turn back towards your building drain. So the downside of A2 is the extra bend in the shower drain.

Cheers, Wayne

 

[Sponsor]

 

[Oldtimm]

Hey Wayne,

Thanks for your advice. Seems to me that Option B is going to be the path of least resistance. This makes sense to me on why option A wouldn't be to code. There's just not really a ton of room for option A2 to be done cleanly, and I have no problem with Option B now that I know that the 2" section only applies to the wet portion.

Thanks again!

 

[wwhitney]

I have no problem with Option B now that I know that the 2" section only applies to the wet portion.

A small caveat: that's not spelled out in the UPC wet venting rules, but it seems like common sense to me. I also don't see anything that would contradict the above. For your reference:

Chapter 9 Vents: Vents, 2018 Washington State Plumbing Code | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

Cheers, Wayne