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I am changing the location of all the fixtures in my bathroom. This move will put the toilet and sink on the opposite wall from the stack. I was originally planning on running a vent up the wall with the sink and across the ceiling to connect back into the stack, but this was assuming I would be replacing the 85 year old cast iron pipe with PVC so I could easily add a new connection up at the ceiling height. Now I am considering leaving the existing cast iron stack and trying to just reuse the existing connections.

There is already a vent connection on the stack that is above the height of the sink, so if I could get the pipe over to this connection I could reuse it. However, to do so I would have to come up the wall, across the ceiling, and then back down the wall with the stack (so I use the old vent connection that is about 4 feet from the floor). I can't just route the vent horizontally around the edge of the room as there is a window on one wall and a door on the other.

Would this configuration meet code? It seems to me it would work fine since it will always stay above the "overflow height of the tallest fixture". I am in Ohio, the Ohio Plumbing Code is based on the IPC.

         ║
stack>   ║
         ║
         ║  ╔══════════════╗
         ║  ║              ║   <vent
         ║  ║              ║
         ║  ║              ║
         ╠══╝              ║
         ║                 ║
         ║                 ║
         ║                 ║
drain>   ╠═════════════════╝
         ║
         ║
         ║

EDIT - The drain is 3" and will have a toilet sort of in the middle and a sink at the end (near the vent). The 3" drain may also tie into the tub drain or I could connect the tub to the stack separately (the tub is right next to the stack so I have more options).

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    The toilet should not be further than 5' from the stack, so make sure your within that range.
    – Tester101
    May 23, 2011 at 14:00
  • @Tester101 - It will be about 5' or 6' from the stack but the "developed length" of the pipe will be more like 8' as it has to turn to get to the stack. I have read about this same requirement online but I can't find any reference to it in the OPC and the building department did not mention it when I initially got my permit (though he may not have realized the distance from my drawings).
    – auujay
    May 23, 2011 at 15:16
  • 1
    905.2 Grade. All vent and branch vent pipes shall be so graded and connected as to drain back to the drainage pipe by gravity. (IPC 2006). This might prevent you from doing what you want, since your lower horizontal connection would have to slope toward the stack. Not sure if this is allowed or not, but it might be something to look into.
    – Tester101
    May 23, 2011 at 18:56
  • 3
    Distance from the stack is determined by trap size and the slope of the drain line. IPC table 906.1 Trap Size=1 1/4" - Slope=1/4" per foot - Distance=5'. Trap Size=1 1/2" - Slope=1/4" per foot - Distance=6'. Trap Size=2" - Slope=1/4" - Distance=8'. Trap Size=3" - Slope=1/8" - Distance=12'. Trap Size=4" - Slope=1/8" - Distance=16'
    – Tester101
    May 23, 2011 at 19:06
  • I would accept your second comment as the best answer so far (if it was not a comment).
    – auujay
    May 25, 2011 at 2:38

4 Answers 4

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905.2 Grade.

All vent and branch vent pipes shall be so graded and connected as to drain back to the drainage pipe by gravity.

(2006 International Plumbing Code).

This might prevent you from doing what you want, since your lower horizontal connection would have to slope toward the stack. Not sure if this is allowed or not, but it might be something to look into.

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A vent must not allow accumulation of trapped air/gasses. Bending downwards would probably not be acceptable.

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  • 1
    How do you account for kitchen island vent loops?
    – Craig Tullis
    Aug 16, 2015 at 22:33
  • Faecal methane is a dangerous and explosive gas that have blown apart sewer covers, and houses.
    – Blessed Geek
    Aug 17, 2015 at 0:04
  • @Craig you can bet that nearly kitchen island sink is not vented properly. I saw them do it according to code on TOH and the amount of work they had to do for it was ridiculous.
    – Jason Hutchinson
    Aug 18, 2015 at 17:41
  • Condensation (liquid water) can also form inside a vent pipe and has to be able to drain back.
    – StayOnTarget
    Feb 28, 2018 at 0:33
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I'm guessing it would be against code, but I've never looked this up, so maybe some others will chime in. For all practical purposes, you don't want a space where anything (moisture) can collect and cutoff the airflow, grow mold, etc. If in the connection to the vent stack there is no area for water to get trapped, then you might still consider it. But I'd also look into a one way cheater vent that could be installed behind the sink and be done to code.

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In the UK, in some cases, you can use an “air admittance valves” for a toilet, rather than a vent pipe provided you have a stack between it and the public system.

The ideal is that when you flush, a “surge” of water goes down the pipe. The air in front of the “surge” needs to be able to escape out of the way by going up the stack, and air must be able to get in behind the “surge”.

Check if your local codes allows such a setup.

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