WET VENTING A TOILET TO A SHOWER AND TWO SINK CABINET

Discussion in 'Toilet Forum discussions' started by tj1dish, Apr 1, 2021.

  1. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Sure, if there's no downside to 2", go for 2". But if you're drilling studs for the lav trap arm, 2" needs a bigger hole, so that's at least some downside. If your lav trap arm is under 42", 1-1/2" would work and be better for the studs; but I don't know to what extent 2" would work better, and thus how to weight the competing interests. [And either way I'd use stud shoes, so maybe the downside to 2" is minimal.]

    On your last layout, looks good. [Edit: inaccurate commentary removed, see below for update.]

    Cheers, Wayne
     
    Last edited: Apr 9, 2021
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  2. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    OK, so I'm a little unclear on the trap(s) and trap arm(s) for the two lavs--are the lavs sharing a trap? Because the pictures seem to show a single san-tee for the lavs, rather than a double fixture fitting (unless they all just happen to be lined up to block the rear side inlet).

    It's 2 DFUs either way, so for the part of the piping pictured it doesn't matter. But it bears on my trap arm comments; if it's a single trap for both, it can be 1-1/2" and a 1-1/2" trap arm to a single san-tee, if it's within the length limit of 42". If it's two separate traps and the horizontal fixture drains combine to join the single san-tee in the photo, then the minimum sizing would be 1-1/2" trap - 1-1/2" trap arm - 1-1/2" upright combo for dry vent takeoff (to be revented to the other vent) - 1-1/2" fixture drain - 2x1-1/2-1/2 combo to combine the 2nd sink trap arm with the first sink fixture drain while wet venting the second sink - 2" horizontal drain to 2" san-tee.

    As to the picture, we decided earlier that 2" is OK between the sink(s) san-tee and the shower san-tee, with 3" required below it. And upsizing the WC to 4" is obviously fine if that makes sense. So my only further comment is whether it makes sense to extend the 3" portion up into the wall to have a 3" cleanout behind the lav, with the 3x2 bushing in the cleanout tee inlet. The 3" cleanout tee wouldn't fit in a 2x4 wall (hubs are 4" OD), so if that's the condition, you'd need to have a gap in the wallboard for the cleanout tee and below, but it would be hidden behind the lav cabinet.

    Cheers, Wayne
     
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  3. tj1dish

    tj1dish New Member

    Joined:
    Apr 1, 2021
    Location:
    Texas
    Wayne,

    Thank you for your response!
     
  4. tj1dish

    tj1dish New Member

    Joined:
    Apr 1, 2021
    Location:
    Texas
    I see I never actually mentioned it before but I'm planning on a double wall - the existing one (4" ) to stay as a sound-reducing wall and another 4" plumbing wall on the bathroom side, so that way I'll have on hand total of 7" inside the sheetrock to play with.

    For the two lavatory sinks I have two options:

    1) use separate 1-1/2" trap arms for each sink, dry-vent each and stack the drains to the vent, but now I'm thinking that this turns the bottom one to a part of the wet vent so I might have to extend the 3" to above the clean out that will be above the two sink trap arms.

    2) use an all hub double santee, dry-vent both but then the drain for them has to be 2", connecting back to the wet vent - that brings me back to use a 3" up to the clean out.

    So, either way I might have to use a 3" wet vent, just like original pictures 2 and 3 that I posted at the beginning except my clean out to be 3" too and then continue up with a 2" dry vent roof run. Hopefully that 2" roof run would be sufficient for the whole set up and would not call for syphoning later on...

    Please advise?
     
  5. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Okay, I neglected to look at your 3D rendering yesterday and resolve that with your mockup.

    The geometry in your last picture would put the shower san-tee behind the WC, presumably in order to keep the shower trap arm under 60" (UPC limit for 2"). Can you possibly get the shower san-tee behind the lav cabinet? The WC space has to be 30" wide (maybe 32" or 36" would be nicer), and if the shower is 4' wide and the drain centered, that would be another 24". So that seems on the edge of doable, maybe not.

    As to your last post, I would suggest putting the cleanout as low as is accessible, preferably below the lav sink connections. And it would be more useful to have it in a 3" section than in a 2" section.

    As to the minimum size of the vertical portions of your stack, I think the analysis of 908.1.1 in my second post still applies:

    - The dry vent has to be at least 2" because of the WC.
    - The drain/wet vent portion that is carrying 1-3 DFUs from lavs (2 in your case) can be 2", as long as there are no more than 8 DFUs being vented from below. [Minimum drain size is 1-1/2" for a vertical drain with up to 3 DFUs; minimum vertical vent size is 1-1/2" for 8 DFUs; 2" pipe is one size bigger.]
    - The drain/wet vent portion that is carrying the shower has to be 3" [minimum drain size for a shower is 2", so the vertical wet vent needs to be 1 size larger, or 3".]

    Cheers, Wayne
     
  6. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    P.S. I do like Reach4's suggested layout, it lets you put the lav san-tee wherever you like, the lav drain swings around the WC closet flange under the slab so it can meet the shower drain first as the UPC requires. The length limit on the WC fixture drain is 72" from the closet flange to the wye where the shower drain comes in, but half the WC space, plus half the shower width, plus a little extra for the fittings should be well under 72".

    Cheers, Wayne
     
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