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Thread: Enough Venting? - 3d models attached

  1. #1

    Default Enough Venting? - 3d models attached

    I am looking to set up the bathroom as pictured below.

    Normally I would run a nice big stack up one of the side/interior walls of the bathroom and tie in to that. However in this bathroom there are heavy duty beams on each side of the bathroom supporting the bathroom side walls. The only decent place for me to get to the basement and the main stack is out the 'front' which is under the door. From there I can go down an interior wall and end up in the basement and work my way to the stack.

    Since it is under the door I cant go straight up at that point with a vent, I am concerned about proper venting for the toilet(among other things)

    I am wondering the following
    1. Based on the attached drawing do I need a seperate vent for the toilet? I can add another wye closer to the toilet and go back toward the rear wall and get a 2" or so line in to the attic. Not easy but could be done.
    2. I am assuming all the blue pipe would be 3" and the red would be 2" . I assume shouldnt go down to 1 1/2" Can I go down to 1 1/2" as a vent once I get above the shower and sink fixtures?
    3. Is there anything glaring wrong with my layout?

    1. I realize the wye's off the 3" line need to be pointing up at 45 degrees or greater. I am not sure if my diagrams skills reflect that.
    2. tub trap is not shown
    3. 1/4" per foot slope on all drains
    4. sink will not be pedistal. it will be a regular sink cabinet. That big beam is in my way to come up right behind. My plan was to come up from a long sweep as close to the beam as possible and then use (2) 45s to get my in to the wall cavity, hoping to mimimize the backing up of the cabinet.
    Attached Images Attached Images     

  2. #2


    thanks in advance to nelsonba... I took his sample bathroom and all his components to make my diagram... his work saved me tons of time...

  3. #3


    One other concern i have is that the vertical drain pipe is going down a 2"x4" wall.. Since the wall is 2"x4" the 3" pipe will just fit and my 90 fitting will have to start above the top plate of the wall.

    The joists are 9 1/2" inches high. Is 9 1/2 inches high enough to stick a 90 on one end, get some slope over about 7' and then get a closet flange on the other side..

    If the closet flange comes down 4" to the middle and the 90 comes up 4" to the middle I dont have much left for slope.

    I dont think the closet flange will come that far down especially since I have 2 1/4" of sub floor(radiant floor) and the bend will start up a little higher.

    should I be concerned?

  4. #4
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default drains

    You should be able to work the elbows into the ceiling, but a more immediate concern is that each of those drawings shows the vent going into the bathtub trap. It CANNOT do that, it has to be connected to the pipe between the trap and the connection to the 3" main.

  5. #5


    that makes sense... duh...

    do those branches need to be 2" or would 1 1/2 work? looking at my current tub it is 1 1/2 inches.

  6. #6
    Commercial Plumber markts30's Avatar
    Join Date
    Sep 2006
    Phoenix, AZ


    I believe the WC vent has to be 2"... A tub drain can be 1 1/2" but it must up-size one pipe size (AFAIK) when wet-venting...
    In this case, min pipe size is probably the 2" shown...
    Final verdict on what is legal depends on where you are located as code differs from one region to another...
    post your location and someone local can probably give you a better idea...

  7. #7
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default drains

    In the long run 2" branch drains will be better. The tub and sink vents can be 1 1/2".

  8. #8


    Unless I'm misinterpreting the drawings some way, you're not doing too well here. First of all, the closet cannot be wet-vented by a tub. Secondly, the tub trap is in the wrong place. In your first post, you say that the tub trap is not shown, but there's a trap there, at the base of the stack, that does not belong.

    By notching the wood a bit, you should be able to get into the wall behind the sink with two forty-fives, and eliminate the elbow.

    I'm basing my statements on the UPC code. I don't know what your code is.

    Also, I'm assuming that, when looking at your drawings, there is a floor below this or that there is some other reason for you to horizontally vent your toilet. Horizontal vents are only allowed in the UPC if there is some structural problem that does not allow for the vertical continuous waste and vent system.

    In order to vent this correctly (again, according to UPC), and assuming that you have structural conditions which preclude you from vertical vents, then you could add another wye/45 combination between toilet and tub and pipe it back to the other vent somewhere. Also, if you are on a normally-vented line, you don't need to roll the pipe up above the invert, so both the sink and tub could simply grade to the main line. (And that assumes that you do not try to use the tub vent for the toilet vent.)

    The vent for the toilet must be 2". The drain and vent for the basin can be 1-1/2," and the tub drain must be 2" while the arm and vent can be 1-1/2" (The "arm" is the pipe from the stack to the trap.)

    In addition to all that, the code requires a minimum amount of venting for a house. Here, we are required to have a 4" main drain going out the footing of the house, and so are required to have the equivalent of 4" of vents as well. In some areas, it depends up on the number of fixtures in the house - for example, if you had two toilets, the main drain would be required to be 3" pipe and the vents could also be 3". It depends on what your code says. This can be a problem when tying new bathrooms into existing vents - assuming that there is enough venting on the house because there was enough before. If your plumbing was legal before, and you're adding a bathroom and putting a new 2" vent through the roof, you're good to go.

  9. #9


    those comments were very helpful. yes this is an addition over finished space. the bathroom walls dont line up with any walls below so I need to travel some distance to find a place I can go vertical.

    I was looking at it again today and I could add an additional wye before the tub to vent the toilet. I will do that... it makes sense.

    the point about the knotching is good too..

    my problem now is that I opened up the wall that I planned to go down.. there is a ton of electric, I will need to find a new way down.


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