Shower and tub horizontal drain

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by cadobe, Sep 9, 2021.

  1. cadobe

    cadobe Member

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    May 25, 2019
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    Seattle
    Hi,

    Is it possible (WA code allowance) to use the Double Fixture 3" Hub to be used on both shower and tub drainage?

    [​IMG]
    I like to have the side ends for shower and tub. The long straight end goes to the 3" drain pipe and the opposite used for cleanout.

    Edited: the fitting needs to be on horizontal position.
    Thanks.
     
    Last edited: Sep 9, 2021
  2. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    You can use that fitting for drainage with the barrel vertical, or up to 45 degree off vertical. And as you are talking about using the top for a cleanout, you'd need to have already vented the tub and shower trap arms

    Cheers, Wayne
     
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  4. cadobe

    cadobe Member

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    the fitting needs to be on horizontal position, I need that
     
  5. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Then you need to use a fitting with the equivalent sweep of a long turn 90. And you can't use a fitting with 4 openings that are arranged in a cross pattern, as if the barrel is properly sloped, the two perpendicular entries will be at best both level. But those entries need to be sloped at 2%, so you'd need a cross with the two side arms pulled up out of plane.

    The always allowed option is to use separate fittings for the tub and shower coming in, each one gets a horizontal combo or wye, one after the other. That lets you set the slope of each branch inlet separately. At least one of the two trap arms will need to be vented; if only one is, it will wet vent the other, assuming the trap arm complies with the length and fall limitations.

    If you need the two fixture drains to come into the combined branch at exactly the same place, the only option is the double wye. If you pitch the barrel of the wye at 2%, the side inlets will be sloped at 1.4%, so some jurisdictions say that the double wye isn't allowed. However, it seems fine to me if you slope the double wye barrel at 3%, then the side entries are sloped at 2%. Each side entry on the double wye gets a 45 (often street), which you can rotate a little so that its inlet is at 2%.

    Cheers, Wayne
     
  6. Jeff H Young

    Jeff H Young In the Trades

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    vertical only. use a combi and a wye and 1/8th bend to put everything in alignment.
    im not asking why your tub and shower need 3 inch lines instead of 2 inch
     
  7. cadobe

    cadobe Member

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    Yeah, sounds the safest way not getting backed-up by inspector.
    However, another question that I ask myself is about the venting. Was planning to use 3" drain pipe that allows me to have the vent stack ~ 8ft away from the shower and tub trap.
     
  8. cadobe

    cadobe Member

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    I have the vent over 5ft away from the traps, to the other side of the wall where the shower and tub takes place
     
  9. wwhitney

    wwhitney Well-Known Member

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    How about a floor plan showing the tub drain and shower drain locations, the stack location, and any walls that you could use for running a vent? And how about the WC and lavs? Does your stack have any drainage from a floor above?

    Cheers, Wayne
     
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  10. cadobe

    cadobe Member

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    [​IMG]
    Thanks Wayne, single story house
     
  11. Jeff H Young

    Jeff H Young In the Trades

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    I haven't done much horizontal wet venting , but it looks pretty doable I'm just wondering if the shower and tub would be considered on the same trap arm which was always illegal so at most 2 3 inch trap arms might be the ticket . pretty straight shot for the w/c and lav is a snap. that tub and shower just a bit foreign to me
     
  12. Jeff H Young

    Jeff H Young In the Trades

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    oh don't forget the cleanout
     
  13. John Gayewski

    John Gayewski In the Trades

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    Why can't you add a vent on the exterior wall? Pretty easy to pop out through the roof and add a boot I just did it yesterday. It will give you a better performing system.
     
  14. wwhitney

    wwhitney Well-Known Member

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    So, I'm not sure which way the joists run, but a standard wet vent solution could look something like the drawing below. Purple is 3", green is 2". If you need to tie in at the end of the red 3" line you drew, you could of course jog back to the location. The 3" purple line running up and down the page needs to be located so that the tub and shower trap arms both comply with the 5' limit on a 2" trap arm. And the WC needs to be (wet) vented by the lav within 6' of the closet flange, so you might have to route the lav drain to hit the 3" purple line closer to the WC to comply with that.

    Note that the unamended UPC require that the WC be last on the wet vent, but my understanding is that Washington State has deleted that requirement.

    Cheers, Wayne

    b.jpg
     
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  15. cadobe

    cadobe Member

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    Yep, yep....the most reliable solution. I should probably run 3" pipe on green line too just to be on the safe side. Thanks Wayne.

    In the drawing the WC is not the last item, not sure on the way is counted. If not where would be the place for the WC in order to be last?
     
  16. wwhitney

    wwhitney Well-Known Member

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    That's unnecessary and would be highly unusual. If you are running the drains through your joists (rather than in a crawl space), it might also involve excessive drilling of large holes

    As to "last", that's in the direction of flow. In the drawing, the tub is last, and the lav/WC are first. [First is only definable as far as the first joint.]

    Cheers, Wayne
     
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  17. cadobe

    cadobe Member

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    I see now, nice explanations.
    I do not have floor joists. The floor is tong and groove planks supported by a central beam that runs on the length of the room. I've added an additional beam parallel to the original one, running on the tub center-line to make sure floor will hold a full filled tub. Drain pipes I will run them under the beams it is not a problem in a crawlspace, the only thing that I need to probable re-route is the water supply/return to a towel warmer radiator that is located by the window on the left side. That's OK.
     
  18. wwhitney

    wwhitney Well-Known Member

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    BTW, two points on my drawing:

    1) The first bend on the WC drain line is supposed to be a 45, but what I drew looks more like a 60.

    2) Moving the lav drain to go through the floor closer to the toilet would slightly simplify getting the shower and tub to join the branch drain after the lav (which is a requirement). So depending on where the sink is within that cabinet, and how easy it is to move the 2" vent, or jog the vent within the wall to line up with the current vent, I would consider that.

    Cheers, Wayne
     
  19. cadobe

    cadobe Member

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    But 60 is not better than 45?

    The distance from the sink vent to the WC flange is exactly 4ft
     
  20. wwhitney

    wwhitney Well-Known Member

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    Well, two things: the way I drew it looks like it would take a 30 degree elbow (60 was a typo), which doesn't exist. If the geometry works out you could use a 22.5, that's better than a 45. The constraints are getting the up-down the page purple 3" drain close enough to the tub and shower to comply with the 5' trap arm rule, and getting everything connected in the correct order (the first joint has to be lav/WC).

    As to 60, for whatever reason its bend radius (in plastic) is tighter than a 45: (3) 60s in succession would be like 2 quarter bends, while (4) 45s in succession would be like 2 long turn 90s. So I would think it makes sense to only use them for horizontal to vertical bends, not horizontal to horizontal or vertical to horizontal. Although I don't think that's actually a code requirement.

    Cheers, Wayne
     
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  21. wwhitney

    wwhitney Well-Known Member

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    P.S. Just to be sure, with horizontal wet venting and all your pipes at an elevation below the beams, your shower and tub p-traps will be below the beams as well. A 2" trap arm is allowed to fall at most 2" before it's vented, and the shower and tub trap arms are getting vented by their connection to the 3" branch drain.

    Cheers, Wayne
     
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