Adding a new soil/vent stack for new bathroom?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by SD-777, Jan 14, 2021.

  1. SD-777

    SD-777 New Member

    Joined:
    Jan 14, 2021
    Location:
    NJ
    I have a walk in closet in my 2nd floor master bedroom that I'd like to convert into a full bathroom. I already have a 1st floor half bath and a 2nd floor full bath which each have their own stacks (2nd floor was an addition from previous owners) but it would be very hard to reach that stack because the floor joists are running perpendicular to where drain pipes would need to be run. What I would like to do is run a completely new stack just for the new bathroom, I could frame around it as on the first floor it would run behind the kitchen cabinets so can be easily hid.

    Enclosed sketch: On the right side the stack servicing the 1st floor bathroom is the original cast iron stack from the house. The 2nd floor stack is pvc tied into the main sewer (septic in this case) line. Just to give all the details I included a pump running into the sewer line from a basement sink as well as the kitchen drain which is tied into the sewer line. I don't know how the existing bathrooms are vented because it's all behind walls, but I'm assuming they make sense and I won't be disrupting them.

    So I had a few questions:

    1) Firstly being if this is feasible at all? The alternative would be to get into boxing out and sistering joists, accessing the stack inside the wall/floor for tie in, and such and I 'd really like to avoid that.

    2) Can I tie the 3rd new stack into the 2nd floor stack at the basement as I sketched, or would I have to tie it directly into the sewer line? There really isn't any room to tie anything to the main sewer line, although I could consider moving the basement sink pump and tie the new stack into there, but that would introduce more turns. If I could avoid cutting and working with the cast iron pipe I'd prefer that, but I feel comfortable with any PVC work. I would slope it appropriately and tie into the existing 2nd floor stack, I'm assuming with a wye fitting?

    3) On the 2nd floor I would vent the sink and tub according to code, which I believe is 3ft above the highest rim but I would have to check that. Is it possible to vent the new sink/tub into the existing 2nd floor bathroom vent inside the attic? I would like a avoid having to make another hole in the roof, but am assuming the new stack needs to be vented somewhere anyway so I may not have a choice.

    4) Can I combine the sink/tub drain and then tie that into the new stack? Or does each need it's own separate tie into the stack? I'm trying to figure out how to connect all 3 fixtures with the limited space inside the floor. Also could I combine the sink/tub vent and then tie that one vent into the stack, or do they also have to have separate tie ins to the stack?

    5) Dumb question, but the toilet doesn't need to be vented right? Well it's already vented by the stack so I don't need a separate vent like the tub/sink do?

    6) The 2 existing stacks are both 3", would I use 3" or consider 4" to be safer? I'm most concerned about when it enters the basement to where it ties into the sewer line is about 12 feet. I have plenty of room to slope it appropriately, but did not know if such a long run would require a larger pipe. There would also have to be a couple of horizontal turns (or maybe a single 45 turn) as the sewer line sticks out a few feet from the wall.

    Thanks all in advance
     

    Attached Files:

  2. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    1) Yes, on the DWV side. I don't know anything about septic and whether you might be overloading the capacity of your system.

    2) You can tie into the vertical section instead of the horizontal section. For the vertical tie in you have a choice of san-tee or combo (wye + 45)

    3/4/5) 2nd floor bath layout is basically independent of anything discussed so far, and would be best done with a floor plan showing fixtures, which way the floor joists run, where you can put the new vertical drain to the basement, and where other vents you might want to tie in to are located. You don't have to extend your new vertical stack through the top story and the roof to be a vent terminal; there are certainly layouts where the vents are all located away from the drain stack.

    6) 3" would be fine. Minimizing horizontal bends is best practice. When you accumulate too many horizontal bends, a cleanout is required, but I'm not familiar with those rules.

    Cheers, Wayne
     
    Last edited: Jan 14, 2021
    SD-777 and Jeff H Young like this.
  3. Sponsor

    Sponsor Paid Advertisement

     
    SD-777 and Jeff H Young like this.
  4. SD-777

    SD-777 New Member

    Joined:
    Jan 14, 2021
    Location:
    NJ
    Awesome thank you!

    2) So I can tie into the vertical section of one of the existing stacks? That's how I tried to draw it on my diagram.
    3/4/5) I'll put together a diagram for that. So if I didn't tie in any vents to the drain stack would I just cap it off? Then I could run the vents to the existing vent stack in the attic.
    6) I can just run it diagonally from the wall to the tie in, not a big deal as it's just running over the washer/dryer in the unfinished part of the basement. Then I wouldn't have any horizontal bends at all.
     
  5. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    2) Two pipes, which are drains that have already been vented, and which aren't being used as wet vents, can join anyway you like. Each drainage path just has to obey the slope and change of direction rules individually. So no joining a vertical drain to a horizontal with a san-tee on its back, it has to be a combo.

    3/4/5) I'm not sure I follow the question. If you put together a floor plan for the upstairs bathroom as requested, we can discuss.

    I think you might be asking, for the vertical drain line that runs through the 1st story and receives the drainage from the 2nd floor bathroom, if none of the fixture connections to that vertical drain rely on a vent takeoff in line with the vertical drain, would you just let the drain rise up to a cap? And the answer is no, you wouldn't extend it above the incoming horizontal drains at all. I.e. where the uppermost horizontal drain comes in to turn vertical, you'd use a quarter bend, rather than a sanitary tee. So there's nothing to cap.

    But perhaps I have misunderstood your question.

    Cheers, Wayne
     
  6. TheMostHackEver

    TheMostHackEver Member

    Joined:
    Feb 3, 2021
    Location:
    Mississippi
    Septic systems are sized based off the number of bedrooms and or any high volume fixtures, like big tubs.

    The number of bathrooms isn’t relevant when sizing septic in my locality.
     
  7. SD-777

    SD-777 New Member

    Joined:
    Jan 14, 2021
    Location:
    NJ
    2) so I will tie into the vertical portion of one of the existing waste pipes, I uploaded a picture and illustrated where I would tie in. I would run the 3" waste line from the 2nd floor to the far end of the basement, then would run it along the ceiling (sloped) to the waste pipe, then run it vertically a few feet and connect with a sani tee. I just have to figure out where along the line I could also tie in the waste pipe for the sink/shower, can I run these directly into the new toilet waste line?

    3/4/5) Enclosed floor plan. There is only one vent inside of the wall adjoining both bathrooms which goes into the attic, I'm not certain how they all connect as they are behind walls. For the new bathroom I'd like to vent the new sink and new shower up into the attic and T into the existing vent so I don't have to make any new holes into the roof. Enclosed picture of attic vent also.

    The floor joists run parallel to the adjoining wall so it would be easier to tie the shower drain to the other bathroom's existing shower drain, is this feasible? Or do I have to run a new drain? A new drain would entail running it across the room to the sink side.

    For the toilet you are saying I just have to go from the toilet to the waste pipe via an elbow with no vent?
     

    Attached Files:

  8. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    2) The basement drain portion sounds fine. To join the vertical in the picture, it would be better to use a wye than a san-tee, as you'll be coming from above. Depending on the details, it might make sense to redo that double 45 jog, it's hard to tell from the photo.

    What are those small diameter lines going into the former cleanout on the bottom white combo? They look suspicious and the configuration may not be correct. When you tie into the vertical there it shouldn't be too hard to fix those at the same time, if necessary.

    As to the sink/shower, if you mean the new upstairs sink and shower, they would typically combine with the new WC drain upstairs, so you'd just have a single 3" line coming down to the basement from the new full bath.

    3/4/5) If you can map out all the drain and vent piping of the existing bathroom, then you will be able to determine whether you can using the adjacent bathroom for the shower drain and vent tie-ins; probably you will be able to, because the IPC allows wet venting for 2 bathroom groups. Otherwise, you'd have keep all the new work separate and bring the shower drain over to the new sink/WC. What size are the floor joists?

    As to configuring just the WC and sink that are against the left wall (leaving the shower out of it for now), it would go something like this: a 1-1/2" san-tee in the wall behind the sink, the top is the vent for both sink and WC; the 1-1/2" drain goes down into the floor system and joins the 3" WC drain on the horizontal, to wet vent it; the combined drain goes to your 3" stack location and turns down with a quarter bend. So yes, an elbow with no vent take off at that point, as the lav drain has already wet vented the WC.

    A dimensioned floor plan, showing the joist sizes and locations, and the location where the 3" stack below will be, would be required to provide more specific guidance.

    Cheers, Wayne
     
    SD-777 likes this.
  9. SD-777

    SD-777 New Member

    Joined:
    Jan 14, 2021
    Location:
    NJ
    Thank you again, awesome information.
    Enclosed dimensional floor plan. Joists are running as noted 16" on center and they are about 7 1/2" wide. Also the septic is a 1000 gallon system so it's rated for 3 bedrooms, but no plans on adding any bedrooms.

    -Wye to vertical stack got it. The jog is to go around HVAC so I don't think I can eliminate it without getting into HVAC.
    -The piping coming into the cleanout is from a basement sink pump, that's how it was when I moved in, is that against code?
    -I reversed the sink/shower from my previous drawing in my new dimensional. So in my diagram the stand up shower would drain directly to the toilet waste and vent up to the attic and tie into the existing vent before it exits the roof, is that ok?
    -The sink on the opposite side of the room is the issue, I don't want to go pull up the floor and go through joists (although I will if I have to) can this be tied into the shower drain from the existing bathroom? Then the sink would be vented up into the attic to also tie into the existing vent before it exits the roof?
    -I'm not sure where the existing bathroom drain and vent piping goes, I think I'd have to start tearing sheetrock out to see that.
    -Pictured the new 3" waste, I'd try to get it as close to the corner as possible as the room below has kitchen cabinets enclosing that corner and it would be very easy to hide the waste behind those cabinets.

    So just to reiterate the big questions are if I can tie in the new sink drain to the existing bathtub drain and if I can vent the new sink and new shower into the existing vent in the attic before they exit the roof?


    Dimensional Bathroom.jpg
     
  10. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Possibly, in that it clearly used to be a cleanout, so now there's no cleanout. It looks like there's a tee fitting as the last small diameter fitting, is there another line coming in that's obscured in your photo? And there's another fitting a little upstream that looks like a vertical tee, do you know what that is?

    I'm not sure if it's required, but it may be a good idea to add another wye where the cleanout was, and plumb the sink pump output into the branch of the wye, with a cleanout in the straight inlet of a wye. (Or vice versa, not sure if one way is better than the other.) Since you'll be doing new work in that area already.

    You don't show the shower drain location, but presumably it's the center of the shower. You'll need to pass a 2" shower drain through 1 or 2 joists to bring the drain alongside the wall on the left of the drawing. That's tight but doable with 7.5" joists--the allowable hole size is 1/3 the joist depth, or 2.5", and the OD of a 2" Schedule 40 pipe is 2-3/8". So you'll have to drill your 2-1/2" hole(s) very accurately. The holes will need to stay 2" away from the top and bottom edges of the joists, so you only have the central 3.5" to work with, meaning you can achieve at most 1" of fall running perpendicular to the joists. But that should be enough.

    Once you are alongside (or under) and parallel to the left hand wall, you can do your vent takeoff with an upright wye rolled up to 45 degrees off vertical. Then the 2" drain can meet the 3" WC drain and wet vent it. In the attic, you can combine vents any way you like (well, they should all be sloped back towards their respective drains, you don't want to create a trap).

    If there's a joist between the toilet flange and the new 3" stack location, that's going to be a problem. A hole for a 3-1/2" OD Schedule 40 3" pipe is too large prescriptively for a 2x8, but there may be a listed repair bracket available to reinforce the joist to allow the hole.

    Likely, but you'd really want to understand or at least have a good guess on how the DWV is configured in the existing bathroom. I think in most configurations you could drop in a vented lav drain without disrupting anything else. I haven't thought about whether it's literally all configurations so you could do it without any knowledge of the existing layout.

    As for the vent for the new lav, it would stay separate until it rises to 6" above the lav flood rim, then it can combine with the existing 3" vent.

    Cheers, Wayne
     
Similar Threads: Adding soil/vent
Forum Title Date
Plumbing Forum, Professional & DIY Advice Moving Kitchen Sink and Adding Bathroom Nov 23, 2021
Plumbing Forum, Professional & DIY Advice Help on adding drain Oct 18, 2021
Plumbing Forum, Professional & DIY Advice Adding shower to half bath in basement Oct 13, 2021
Plumbing Forum, Professional & DIY Advice Adding Laundry Sink Sep 27, 2021
Plumbing Forum, Professional & DIY Advice Adding Washer and Utility Sink in Basement Sep 14, 2021

Share This Page