Can I offset my stack horizontally in this situation?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Sluggo, Mar 28, 2014.

  1. Sluggo

    Sluggo Member

    Messages:
    66
    Location:
    WA
    I am designing a small, new bathroom in an area that was previously rough-plumbed as far as the vents and drains are concerned. The bathroom will have a toilet, a sink, and a shower. This area is slab on grade, and I have 1-1/2" ABS coming up through the slab for a shower vent, and there's a separate pipe for the shower drain. There is a 3" drain for the toilet, and there is a 3" vent stack. All of these are connected properly under the slab and all of these pipes are where I would like them to be, except for the 3" vent stack, which is coming up directly under the front edge of where the vanity has to go. I can conceal this 3" vent pipe inside the vanity base where it comes through the floor, but I need to get it over to the back wall so I can run it up inside the wall. I understand I can do a 45 degree jog to accomplish that. However, I would ideally like the stack to take a 90 degree turn right at floor level, run 18" straight back to the back wall and then turn up 90 degrees so it can run up vertically inside the wall and then through the roof. I intend to connect the shower vent to the vertical portion of the 3" stack well above the flood level of the sink, and -- if it's allowed -- I intend to wet vent the sink into the stack since it would be right there. This bathroom will be in a standalone, one-story studio and the only plumbing connection to the main house is the underground sewer system; this 3" stack would only serve this bathroom. I'm in King County.

    Bottomline question: Does code allow an 18" horizontal offset of the 3" vent stack below the flood level of the sink as long as the venting of the sink, shower, and toilet are done correctly?
  2. Tom Sawyer

    Tom Sawyer In the Trades

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    Maine

    Nope, not if it's dry.
  3. Terry

    Terry Administrator Staff Member

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    15,130
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    Bothell, Washington
    None of that sounds doable in King County.
    I think you are buying future problems. Sometimes I run into homes where things like that have been done, and for decades later they bemoan the fact that the plumbing has big issues. Don't do this to yourself.
  4. Sluggo

    Sluggo Member

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    66
    Location:
    WA
  5. Terry

    Terry Administrator Staff Member

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    15,130
    Location:
    Bothell, Washington
    how about a picture of what you have. normally a 3-inch going up is a wet stack. A standard vent rough-in in a basement would be two inches for the entire bathroom. are you sure that the 3 inch is only a vent?
    Last edited: Mar 29, 2014
  6. asktom

    asktom Member

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    575
    Location:
    Victor, MT
    If it isn't a drain from above you could offset with two 45s and tie in the lav. If putting a san tee on top of the upper 45 sets your lav drain too high you could put the tee between the two 45s, turn the branch to the side and use a 90 to turn toward the lavatory. But, Terry is probably right that it is wet.
  7. Sluggo

    Sluggo Member

    Messages:
    66
    Location:
    WA
    Here is a picture of what I have. I've drawn three options for offsetting the stack in some way. Please comment/advise:

    Number 1: straight back out of the floor and then up the wall:
    V1.jpg

    Number 2: straight back to the wall, 90 degree turn to the side wall, then up:
    V2.jpg

    Number 3: 45 degree bend to the back wall and then up:
    V3.jpg

    I prefer to leave the area underneath the sink open, with just a box at floor level to hide the stack piping, which is why I would like to run it flat along the floor. If I run it up at 45 degrees, then I have to close the undersink area in for aesthetic purposes. The area to the right shows the vent for the shower; the separate shower drain pipe is in the hole just out of sight near that vent. The toilet drain is behind the viewer and is vented by the 3" stack in the picture. The copper piping will be cut down to floor level and routed after I get the venting figured out.
    Last edited: Mar 29, 2014
  8. Sluggo

    Sluggo Member

    Messages:
    66
    Location:
    WA
    asktom-
    There is nothing above. The previous owner got a start on putting in this bathroom and then stopped. I haven't touched any of the plumbing and this is what existed when I bought the place. I want to figure out my venting options before I go in for a permit; I find that I get better outcomes when I know what I'm talking about.:rolleyes:
    Last edited: Mar 29, 2014
  9. asktom

    asktom Member

    Messages:
    575
    Location:
    Victor, MT
    With nothing above you can use 45s to offset, tie in the lav either on the vertical or the slant and tie in the shower vent 42" above finish floor. I know you want to use 90s, but you came here to find out how to do it right and using 90s isn't right.
  10. Sluggo

    Sluggo Member

    Messages:
    66
    Location:
    WA
    asktom-
    Thanks. I would have preferred a different answer, but I wouldn't have bothered you guys with this if I didn't want to know the right answer. If there are no other options, I'll work with that.

    One other thing: I have plenty of room to tie in the sink drain to a vertical sanitary tee. What do you think of putting a cleanout fitting between the two 45's? Necessary? Overkill?
  11. Terry

    Terry Administrator Staff Member

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    15,130
    Location:
    Bothell, Washington
    If that is at the end of a run, you will need a 3" cleanout.
    One cleanout is all you need near the floor. If you decide to 45 right at the floor, the cleanout can be higher than that.
  12. Sluggo

    Sluggo Member

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    66
    Location:
    WA
    Thanks...will do.
  13. bluebinky

    bluebinky Member

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    405
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    Santa Clara, CA
    Have you considered breaking up some concrete?
  14. Terry

    Terry Administrator Staff Member

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    15,130
    Location:
    Bothell, Washington
    3 x 2 x 3 low heal for the cleanout. 2" for the vent. Lav off a 2 x 1.5" santee.
  15. Reach4

    Reach4 Well-Known Member

    Messages:
    2,432
    Location:
    IL
    Here is what I think the floor plan is. Shower entrance on the right? Those copper pipes carry your 1. hot in, 2. cold in, 3. cold out??? huge2.png I don't have answers. I am just reading along.
  16. Sluggo

    Sluggo Member

    Messages:
    66
    Location:
    WA
    Terry-
    Thanks, again. But I want to make sure I am understanding you. After I jog the 3" stack over with the 45's and bring it up inside the wall behind the vanity, is it ok to reduce the stack diameter from 3" to 2" right above the sanitary tee drain connection for the sink?
  17. asktom

    asktom Member

    Messages:
    575
    Location:
    Victor, MT
    You can tie the lav into a 2" vent vent for the toilet. If you do it Terry's way the 3 X 2 LHO can be below a 2 X 1 1/2 san tee for the lav. I might be tempted to use a 3 X 2 wye where you come out of the floor with the cleanout on top and the offset in 2" - unless the clean-out was going to end up right below the trap.
  18. nhmaster3015

    nhmaster3015 Master Plumber

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    836
    Location:
    The granite state
    Where is the toilet drain?
  19. Sluggo

    Sluggo Member

    Messages:
    66
    Location:
    WA
    The toilet drain is 4 feet away from the 3" stack coming out of the slab. It's just behind where I stood to snap the photo.
  20. Sluggo

    Sluggo Member

    Messages:
    66
    Location:
    WA
    A good thought, but I can't break up any more concrete due to radiant heat piping in that area.
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