Re-routing a drain vent line

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Philip in Connecticut, Jan 14, 2009.

  1. Philip in Connecticut

    Philip in Connecticut New Member

    Messages:
    29
    Location:
    Connecticut
    First off, I hope this is the right forum.
    We are planning a remodel of a bathroom in a 1960’s vintage ranch in Connecticut. We would like to remove one of the interior non-load bearing walls in the bathroom, but unfortunately, that is the wall that is used as a chase for a vent pipe. In general, we have two full baths back to back with a common wall between them, where most of the plumbing takes place. The vent line in question t’s off a shower floor drain line, takes a short horizontal run, then goes vertical through the wall (that we are looking to remove) and up into the attic where it ties into the main 3†vent line (which then exits through the roof). I’d like to re-route the vent line coming from the floor drain by connecting into the main drain/vent line at another location. The main drain/vent line starts off in the basement where both toilets, as well as the bathtub and shower feed into it. From there, the 3†line travels vertically through the common plumbing wall, and up into the attic. In that common plumbing wall, the sinks from both bathrooms tie into the line. My idea is to re-route the small vent line from the floor drain, by making a short horizontal run, then a 3 to 4 foot vertical run, then finally a 4 to 5 foot horizontal run where it would connect into the main 3†vent pipe (stack?). I wanted to know if this was OK, and if so, should I be concerned about the pitch of the horizontal run into the main vent pipe, or the height of that horizontal run relative to the fixtures (sinks,etc.) that feed into the main drain/vent line (seems like I came across some thread that indicated that there was a minimum distance above the highest overflow point, which I guess would be the rim of the sink(?).

    Finally, we would also like to build a recessed cabinet into the common plumbing wall, right where the main 3†vent line is. Is it OK to make that 3†line jog around the planned nook in the wall (i.e., 90 degree bend to right, over 10â€, 90 degree to vertical, go past nook, 90 degree bend left, go over 10â€, then 90 degree back to vertical)?

    Thanks in advance for your assistance.

    Phil
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Hard to picture exactly what you are doing but keep these two rules in mind:

    The vent cannot be horizontal anyplace below the flood rim, usually meaning about 42" above the floor.

    Water will not run up hill, not even a little bit. You must maintain slope of 1/4" per foot minimum at all times on the drain lines.
  3. Philip in Connecticut

    Philip in Connecticut New Member

    Messages:
    29
    Location:
    Connecticut
    OK, thanks for the input. I am not planning on modifying any of the drain lines, just the vent lines. I have a vent that now starts just beyond the trap from a floor drain (shower pan). It does go horizontal for about a foot, then vertical, straight up to the attic, where it ties into the main vent pipe. I am proposing to modify this run, so that instead of going straight into the attic, it takes a slight 45 degree jog to get into a different wall cavity. From there it will go up a distance (I think you just told me the minimum height this must be), then it will go horizontal so that I can tie into the 3 inch main vent pipe inside the bath common wall, instead of the attic. Should this horizontal run, which will be carrying no water (?) be pitched? And if it should be pitched, which direction: toward the main vent pipe, or back toward the drain where it started?
  4. Lee Tanner

    Lee Tanner New Member

    Messages:
    15
    I just moved a vent from a wall and took the wall out it was for the washer hook up, Is the vent going to hook up at the same place in the drain line if so that would be ok, if not make its on the same side of the trap and you should be ok, on the main 3" vent you wanted to 90 should be fine, If I am understanding you correctly.
  5. Philip in Connecticut

    Philip in Connecticut New Member

    Messages:
    29
    Location:
    Connecticut
    Yes, I am coming off the drain line from the same T fitting, but I am taking a different path up to the main 3" vent pipe/stack. Instead of tieing into the 3" vent in the attic, I want to run the vent horizontally through the common wall where all the other pipes are located for the various fixtures. I was not sure if this had to be a minimum height above some reference point (spill over from sink, etc.) and I still am not clear on the pitch: do I pitch toward the vent stack, or toward the floor drain?
  6. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    Phillip,
    Picture this...
    If water condenses anywhere in the vent or, if rainwater enters through the roof vent, all the water must run down the vent to the drain without forming puddles or accumilating in the pipe anywhere. In short the entire vent and drain must be pitched to the drain.

    A 45 is okay to move the vent into the next bay but it cannot go to the flat 1/4" per foot pitch below the flood rim of any fixture served by that vent. The intention here is if the drain stopped up glop could get into the flat section and dry blocking the vent.

    I hope that clarifies it for you.
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