I'm attempting to add a bathroom to my 3rd floor. I have to run a 3" waste line through a wall on floor 2, down into the ceiling of floor 1 to tie into the existing 3" waste line connecting the other 2 toilets on floor 2.

Because of the existing constraints, my question is can I vent off the top of the 90 elbow I'm using off the toilet waste pipe that turns the waste pipe vertical down the wall to vent the toilet and shower.

As the image shows I have about 1'4" from center to center of toilet to turn down the wall where I'd like to vent off the top. I have about 4'2" from shower drain to long sweep sanitary wye tie into the 3" waste pipe.

Would this configuration pass code?

enter image description here

enter image description here

  • It will depend on where you live.
    – Kris
    Oct 11, 2020 at 17:29
  • North Carolina Wake County
    – michael
    Oct 11, 2020 at 18:29
  • North Carolina code base on IPC
    – Kris
    Oct 11, 2020 at 21:25
  • I would put a sanitary tee at toilet location and vent up the wall behind it tie into original stack above ceiling height
    – Kris
    Oct 11, 2020 at 21:36

1 Answer 1


Under IPC, not the way you show it. Don't know what code you are under, but they are often similar, while differing in details.

You could have a vent in that location, but there are two immediate problems I see with how you have drawn it.

Vent must be "vertical" (actual definition of "vertical" for this application is 45 degrees or more upward) to 6" above the flood rim of the highest fixture on the floor served - you appear to show it travlling horizontally well below that level. It also cannot combine with any other vents below that level, so if the existing vent passes out through the roof below that level you'll need a new vent out the roof.

Dry vent Tee (or combo Wye) connection to dry vent stack is upside down. For a dry vent connection the bend goes upwards, and the entire vent is sloped to drain back to the fixture drains it serves.

enter image description here

  • Thank you for the response. My drawing isn't scaled super well. The vent exits the roof higher than the flood rim of the highest fixtures on this floor/system. Can I run the vent like that off the top of the 90 horizontal to the outside of the wall area as shown ( < 12") and then go vertical above the flood rim before running it horizontal to tie into the existing vent?
    – michael
    Oct 11, 2020 at 18:25
  • My understanding is that you need to go (at least) 45 degrees upward immediately, not after you get into/through the next wall. So if you come up vertically (or at least 45 degrees up per the definition) as you are heading to the next wall, fine. but not flat when you come off the drain, as your revised drawing (I edited it into your post) shows.
    – Ecnerwal
    Oct 11, 2020 at 18:55
  • 1
    Thus would mean that if a sink is going in this space at least 6” above the rim of the sink.
    – Kris
    Oct 11, 2020 at 21:41

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