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Thread: 2 Toilets, 1 Stack

  1. #1
    Certified Idiot murley's Avatar
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    Default 2 Toilets, 1 Stack

    I am plumbing a house with 2 bathrooms located one over the other. The toilets will be positioned such that they will drain into the same 4" vertical stack. I was planning on connecting the 2nd floor lav & shower into the stack at the second floor level but I read something that said that you cannot drain a fixture above a WC and these would connect ABOVE the 1st floor WC.

    My question is:

    Do I have to run the 2nd floor fixtures down to the 1st floor and connect downline from the 1st floor WC or can they connect below the 2nd floor WC and be OK?

    Thanks in advance for your help!

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    You mean like this?



    You can use 3" on your waste stack.

    And yes, the upper floor needs to connect below the bottom floor or you will suck all the traps dry on the way down.

  3. #3
    Certified Idiot murley's Avatar
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    Wow Terry, that diagram looks crazy busy! LOL

    This is what I was originally thinking...

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  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default drains

    You were thinking "wrong". You are thinking like someone who was told, "Anyone can do plumbing. All you need are some pipe, a bunch of fittings, and some glue".
    Licensed residential and commercial plumber

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Once a pipe becomes a drain, it can no longer be a vent with a few minor exceptions and this isn't one of them.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    Forum Admin, Expert Plumber Terry's Avatar
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    Wow Terry, that diagram looks crazy busy! LOL
    Mine had all of the proper drains and vents.
    If you would like to see a wet vented version, it looks like this.



    You could easily add a wye off of your main line with a vent between the toilet and main line, run the vent for the downstairs toilet up to the second story and tie in at 42" there.

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    Last edited by Terry; 06-11-2013 at 03:06 PM.

  7. #7

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    Confusing thread. Terry, in post #2 you say "the upper floor needs to connect below the bottom floor or you will suck all the traps dry on the way down". In your drawing in the last post, you simply add a vent to the trap arm of the toilet.

  8. #8
    Forum Admin, Expert Plumber Terry's Avatar
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    The lower floor must vent "before" it enters the line. Not confusing at all.

    Without the vent, water and air will push water out of the lower bowl. There has to be a path for that pressure to go.

  9. #9

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    I understand the need for a vent, but it seems to be a common theme on other threads that if a stack services fixtures on a floor above, then it cant service fixtures on the floor below it. Maybe if posts #4 & #5 above stated that the OP's plan would work if he simply added a vent to the WC before it entered the stack, confusion would be avoided.

  10. #10
    Forum Admin, Expert Plumber Terry's Avatar
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    Maybe if posts #4 & #5 above stated that the OP's plan would work if he simply added a vent to the WC before it entered the stack, confusion would be avoided.
    It's hard to explain why things work to newbie's
    If you show them a correct drawing, they change it to fit their way of thinking.
    That is one of the reasons we have building inspections in the US.
    Homes are built and financed by banks. The banks and the future buyers of those homes want to know that the bones and workings of a home are safe and secure.
    I realize that those not in construction think this stuff is really simple, and after a few years working with it daily, it does start to get easier. There are so many things to explain that it would take years and years to start denting it on a casual basis.
    Last edited by Terry; 12-23-2013 at 09:10 AM.

  11. #11
    DIY Senior Member houptee's Avatar
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    Default

    I posted this on a old thread yesterday that was similar question as this thread.

    I have a vertical 4" stack that serves the entire 2nd floor which has a toilet, tub shower, vanity sink, kitchen sink, and a washing machine. This layout was all existing, and this 4" stack continues up thru the roof as the vent.

    The 4" is all cast iron on the 2nd floor, and the other drain lines tied in are 1 1/2 copper.

    The washer was added years later and the plumber cut the cast iron 4" vent section that went up thru a closet in the bathroom and ferncoed in a section of 4" pvc with a sanitary tee for the 2" trap for the washer.

    The 2nd floor transition tee under the floor by the toilet is a 4" cast iron combo wye laying on its side, with cast iron 90s on both ends, one 90 goes up to the roof, and one down, and it drops thru wall in corner of the 1st floor bathroom, into the crawlspace, where it changes to PVC with a shielded fernco, makes a long sweep 90, then a 4" PVC wye ties the 1st floor toilet, tub shower, and vanity into the horizontal 4" drain section. It then 90s at foundation wall, goes outside has a 2 way clean-out tee, then at the curb another clean-out.

    So the 4" stack is also serving as the only vent for the 1st floor bathroom, and also the entire 2nd floor.

    I want to remove all the cast iron and copper and do it all in PVC since I am remodeling upstairs bathroom and kitchen and have the sub floor out since it was rotted under the tub.

    It has never clogged in the original configuration, (we owned the house for over 40 yrs), so should I just do exactly what was there but in PVC, using the fitting shown in this post where toilet ties into the stack to replace that huge cast iron combo wye on its side setup?

    The stack is a wet vent but is it ok to leave it as such, since the layout is existing?

    I am in NJ we are using the NSPC 2009.

    Thanks.

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