Bath, kitchen sink, venting question (yes, another one)!

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by StephK, Feb 12, 2021.

  1. StephK

    StephK Member

    Joined:
    Feb 1, 2016
    Location:
    Richmond, Virginia
    Hi Plumber friends - I know, I know, this question has been asked so many times. But I've spent several hours studying up, and I just want confirmation that I"m OK.

    I renovating a current apartment bathroom from below, while someone lives there, b/c I can't wait any longer to put a ceiling up in my new laundry room. The point is, I don't have tons of luxury about changing venting thru their apartment. Right now, I really just want to replace the old (suspicious looking) cast iron and steel pipes.

    I've attached a very rustic drawing of my plans. Currently the kitchen sink drains into a side inlet 90 right under the toilet flange. All would be good if I could just replace that, but I've read mixed messages about that. Also, it's not clear to me if that current kitchen sink is properly vented, so I'm going to add an AAV. I did the same already to the bathtub.

    Could you glance at this picture and tell me if I'm OK. I think the toilet should vent thru that stack/vent, but will it vent instead thru the kitchen sink aav since that comes first?
     

    Attached Files:

  2. breplum

    breplum Member

    Joined:
    Oct 2, 2004
    Occupation:
    Plumbing and heating contractor
    Location:
    San Francisco Bay Area
    Kitchen sink drain lines must be 2”.
    Nothing much else is code. On a technical basis you’re trying to achieve horizontal wet venting to some degree but kitchens are not allowed to be on a horizontal wet vented array.
    Will it work? Yes I think so. Would it pass a plumbing inspection? No.
     
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  4. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    On the tub/lav, if the tub fixture drain from the trap to the connection to the lav is under 6' (for a 1-1/2" tub drain) and falls less than one pipe diameter, then the lav can wet vent the tub. That would mean you don't need the AAV for the tub.

    In general you can't combined two fixture drains until they are both vented, or one is wet venting the other. And wet venting is limited to bathroom group fixtures, so the kitchen sink is not allowed to wet vent the WC.

    Seems like the best choice would be to bring the kitchen drain in after the tub/lav joins with the WC. If you do that, it would allow the lav to wet vent the WC, if the drain between the lav/tub combination and where the WC joins is at least 2". [A WC drain is not limited in fall or length before venting, under the IPC.]

    If you can't wet vent the WC, then another option is to use an AAV to vent it.

    Cheers, Wayne
     
  5. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Hi Breplum,

    Perhaps surprisingly to those of us used to the UPC, the IPC allows 1-1/2" for a kitchen sink fixture drain. 2" would undoubtedly be a better choice, but I gather the 1-1/2" is existing. Virginia follows the IPC, so the drain size is compliant.

    Cheers, Wayne
     
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  6. StephK

    StephK Member

    Joined:
    Feb 1, 2016
    Location:
    Richmond, Virginia
    hmmmm, ya I can't squeeze the kitchen sink into the wc 3" after the lav/tub - that connection is right up at the stack. Curious what diff. it makes to drop the kitchen sink in before or after that tub/lav? I don't quite get the significance there. Either way the WC still hits those connections before it gets to the stack.

    I"ll up the kitchen to 2", that was an oversight.

    I should have said no inspections here, but I still want it to be right!
     
  7. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    The rule is that horizontal wet venting drains must only contain bathroom stuff.

    The logic is something like the household is unlikely to be doing everything in a bathroom at once, but it is more likely the household is doing kitchen stuff plus bathroom stuff at the same time.
     
  8. wwhitney

    wwhitney Well-Known Member

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    Mar 17, 2019
    Location:
    Berkeley, CA
    I'm not sure how much you are reworking, but I don't follow you.

    If there's an existing horizontal wye right at the stack, with one side currently WC/kitchen and the other tub/lav, you just repurpose it. One side becomes kitchen only, and the other side becomes WC/tub/lav. May require changing the size of the wye and/or flipping it around.

    Then if there's room between that wye and the tub/lav wye, you just bring the WC in there. If not, you need to move the tub/lav wye to make room.

    Cheers, Wayne
     
  9. StephK

    StephK Member

    Joined:
    Feb 1, 2016
    Location:
    Richmond, Virginia
    OK, that makes sense. Given that this is a 1-bedroom apt, that one person won't be showering, or toileting, while working at the kitchen sink. But good to understand the reasoning for the code. But my question is, if I move the kitchen to AFTER the tub/lav, isn't the WC still venting thru the lav/tub/kitchen combo? Albeit, it would only be for about a foot before getting to the stack. I
     
  10. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    No, the vent connection for the WC would be the connection to the tub/lav drain, and the intentional vent path would be upstream on the lav drain (wet vent) to the lav dry vent.

    In other words, if you deleted the kitchen drain, and deleted the portion of the stack above the horizontal drains coming into it (but not the part the lav uses for a vent) and deleted the AAVs, that one lav dry vent can vent the tub and the WC as well. As long as the tub trap arm isn't over length, and the combined tub/lav drain is 2".

    Cheers, Wayne
     
  11. StephK

    StephK Member

    Joined:
    Feb 1, 2016
    Location:
    Richmond, Virginia

    Ahhh, right you are. Doh! OK, let me see if there is any way to rearrange those. There is a cast iron connection there that is in good condition so I didn't want to mess with it. But ya, let me see if I can figure that out. I get it now.

    Thanks so much to all of you (AS ALWAYS)!
     
  12. wwhitney

    wwhitney Well-Known Member

    Joined:
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    Location:
    Berkeley, CA
    [I edited my previous post to expand on it a bit.]

    If it's not clear how to reconfigure the fittings, post a couple pictures of the existing.

    Cheers, Wayne
     
  13. Jeff H Young

    Jeff H Young In the Trades

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    Feb 27, 2020
    Location:
    92346
    It sounds like OP is tearing out existing , So me bing a UPC guy would run 2 inch to kitchen, its really uncertain how easy or difficult bringing this old place compliant would be. the side inlet 90 not exactly a good way to plumb it but has survived.
    Some very simple mods to the plan could make this legal as wayne pointed out. structural conditions may make it very difficult or possibly no issue at all to do it right.
    I think a very good workable solution can be found
     
  14. StephK

    StephK Member

    Joined:
    Feb 1, 2016
    Location:
    Richmond, Virginia
    In addition to the very sketchy (not quite leaky, but almost) connections, the other reason to re-do all these pipes is that the current kitchen sink is ALWAYS clogging up. It's amazing how much gunk fills these pipes over the 100 years. So ya, i'm gonna do a 2" pipe, no question asked!
     
  15. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Sometimes a lot of people live in a 1 BR.

    Yes. Must be after all wet-vent bath stuff.


    Anything added downstream of the kitchen waste must be vented first.

    EDIT: if you have the real vent at the shower, you probably don't need the AAV on the tub if distances are right.
     

    Attached Files:

    Last edited: Feb 12, 2021
  16. StephK

    StephK Member

    Joined:
    Feb 1, 2016
    Location:
    Richmond, Virginia
    ya, the tub drain is pretty long ... 1.5" drain and I think it's about 9 feet. Definitely more than 6.
     
  17. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    I think its work able but we dont have a good idea what the structiural conditions are
     
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