need advice on adding to existing DWV layout in basement

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by DanFL, Jun 13, 2014.

  1. DanFL

    DanFL New Member

    Messages:
    5
    Location:
    Georgia
    DIYer in need of some help with the proper way to add to the DWV system in my basement. The attachment shows a picture of the bathroom in question with an isometric drawing of the layout. I have an existing drain and vent that I need to tie into (existing in blue, new in green in the drawing). I'm adding a sink in the bathroom and would like to add a laundry sink and stackable washer/dryer in the adjacent utility room. Here's what I think I know so far:

    1. DFU Values:
    bathtub/shower = 2.0
    single lavatory = 1.0
    toilet = 3.0
    laundry sink = 2.0
    washer = 3.0
    total = 11.0

    Am I exceding the max unit loading for the 1-1/2" vent? If so, I could leave out the washer hook up.

    2. Is there any way to combine any of the trap arms A, B, and/or C?
    3. I'm assuming the correct fitting at A, B, C is a san tee.
    3. Do they all need their own vent that ties back into the main vent as shown in my diagram?
    4. I'm pretty sure the washer needs a cleanout between H and E. If so would I tie this into the existing main vent to roof as shown? Proper fitting at H would be a combo Y - 1/8 bend and not a san tee, correct?
    5. Washer 2" P-trap is min 6", max 18" above floor, with 2†standpipe min 18â€, max 30†above P-trap.
    6. Trap arm B is at the allowable max of 3'-6" to drain (or is this the requirement to the vent?)

    If it would make this easier, I would consider swapping the location of the washer and laundry sink in the utility room. I'm thinking this might allow me to combine the lav in the bathroom and the laundry sink on the same trap arm.

    Attached Files:

  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,136
    Location:
    Bothell, Washington
    If those are vents for the lav, laundry tray and washer, you can do that.
    The tub needs a vent before it enters the main.
    Right now the toilet siphons the tub. I would run a 2" vent for the tub in this case.


    You can't wet vent a tub with a toilet.
    You can't wet vent a laundry tub over a lav,
    You can't wet vent a laundry tub over the washer,
    Last edited: Jun 13, 2014
  3. DanFL

    DanFL New Member

    Messages:
    5
    Location:
    Georgia
    Thanks for that quick response Terry. Yes, the light green lines in the drawing are my proposed vents, but I wasn't sure if I needed all of them or if I could somehow combine the lav and laundry sink on one. Or would that be wet venting the laundry tub over the lav as you stated above? If their trap arms were coming from opposite sides with the drain and vent in the middle, I believe that's OK. Is there no way to combine the drains and trap when they come from the same side, as in my case? The laundry tub trap arm and lav trap arm would be at the same height ideally, so I'd like to combine them if possible. If the only way to do that is by swapping the location of the washer and laundry tub, I'll do it.

    Regarding the tub, that's unfortunate since I've already connected the tub drain and overflow. Can I just redo the overflow with a vent there that ties into the existing vent? The tub drain is only 1-1/4", but you suggested a 2" vent on the tub. Is a 1-1/4" vent not acceptable there?
    Last edited: Jun 13, 2014
  4. DanFL

    DanFL New Member

    Messages:
    5
    Location:
    Georgia
    After giving this some further thought, I think this can be simplified by swapping the location of the washer and laundry sink. Does this look kosher?

    Again, green lines are drains, lighter green are vents, blue is existing. Hope this makes sense.

    Attached Files:

  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,843
    Location:
    Cave Creek, Arizona
    Well, I have had customers who used an installation similar to that and when the pump discharged it sucked the water out of the toilet because the vent was eliminated.
  6. DanFL

    DanFL New Member

    Messages:
    5
    Location:
    Georgia
    Isn't there a path for air down the main vent stack to prevent this? There is also a vent in the sewer basin with the pump - shouldn't that help prevent this too? What would be done to remedy this problem?

    Any comment on my overall revised proposed layout?

    Thanks.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,843
    Location:
    Cave Creek, Arizona
    quote; Isn't there a path for air down the main vent stack to prevent this? There is also a vent in the sewer basin with the pump - shouldn't that help prevent this too

    The discharge "closes" the pipe to air flow, which is why the system is trying to "breathe" using air from the toilet, and the basin vent is immaterial to this problem. The toilet needs its own vent, OR the new fixtures have to attach to the main line BELOW the toilet/tub connection.
  8. Terry

    Terry Administrator Staff Member

    Messages:
    15,136
    Location:
    Bothell, Washington
    It may be that you have a bathroom group there, one vent for three fixtures. All of them rather low flowing during drain down. A washer is a pumped drain, and is not allowed on the wet vent for the tub, which you likely have there. The washer should have come in downstream of everything. Not by dropping it down the vent there.
  9. DanFL

    DanFL New Member

    Messages:
    5
    Location:
    Georgia
    I cut the cap off of the toilet stub to see if I could figure out how things were connected below the concrete. As far as I can tell, the tub drain actually ties into the 2" main drain and not directly into the 4" toilet drain. If I understand this correctly, I believe the tub then is wet vented up that main 2" line into the vent stack. I think that is what you mean by "bathroom group".

    The washer was an afterthought on my part and I'm sure the builder never planned for that when they roughed in the basement plumbing. The basement also has a 2" kitchen drain rough in, so I thought having the option for a washer down there might be good for resale since the whole basement could be rented as an apartment.

    Putting the washer in downstream of everything requires busting up a lot of concrete. I might have to go without...
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,843
    Location:
    Cave Creek, Arizona
    quote; might be good for resale since the whole basement could be rented as an apartment.

    It might also put you in violation of your zoning. In this area we CANNOT put a "second kitchen" in the basement, detached cabana, or room inside the building JUST SO it CANNOT be "rented as an apartment", unless the area is zoned for "multi family living". Then, putting an apartment, or any "living" space in the basement, opens a "can of worms" because of the "egress" and natural lighting requirements, among other things.
    Last edited: Jun 16, 2014
  11. Terry

    Terry Administrator Staff Member

    Messages:
    15,136
    Location:
    Bothell, Washington
    But it would be the right solution.
    If you want the washer, bring in a contractor with a wet saw, you man the wet vac and watch him cut out a nice square to work in. No dust that way. Cut in the wye downstream and get er done.
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