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Thread: basement remodel vent routing question

  1. #1

    Default basement remodel vent routing question

    In my basement is a 2 inch stub along a concrete wall which I would like to to drain a laundry tub and a kitchen sink. The issue I see is that according to what I would like to do (see image), the 2 stub will be inside the cabinet below the kitchen sink with the laundry tub being about 6-7 feet away. I would like to avoid drilling 1-1/2 hole through the concrete wall (which goes in to another room and I can not get the 3 inch stack due to the doorway and an I-beam. So an air admittance valve is likely my best bet. That said I need to address the issue of where the vent will be and how best to vent the KS trap and laundry sink trap. Can I put the AAV near the door and run a "wet vent" from the laundry sink, not sure the KS will vent properly? Any advise is greatly appreciated. The county uses IPC.

    Thanks in advance.

    Son-of-a!


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  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    Each of those sinks requires a 2" drain.

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    Moderator & Master Plumber hj's Avatar
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    quote;
    Each of those sinks requires a 2" drain.

    Since when? They SHOULD drain into a 2" pipe, but the actual sink drains can be, and often are, 1 1/2". The real question is WHY is there a 2" stub out of the floor without a matching vent at the ceiling, if it was intended to be a "real" drain? Even if you could get to the 3" line, because of the I-Beam, you could not connect a vent to it.
    Last edited by hj; 01-27-2012 at 08:30 AM.
    Licensed residential and commercial plumber

  4. #4

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    I am not sure of the WHY, I just know this is what I have to work with. Can I use an AAV? Would one of these work - see images?

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  5. #5
    Test, Don't Guess! cacher_chick's Avatar
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    Quote Originally Posted by hj View Post
    quote;
    Each of those sinks requires a 2" drain.

    Since when?

    My bad.... I don't know what I was talking about.

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    I've plumbed in locations were basically every trap must be 2" except a lavatory. Tubs,showers,laundry sinks,washing machines,kitchen sinks all were required to be 2"

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    Forum Admin, Expert Plumber Terry's Avatar
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    I like this drawing.

    The kitchen and the laundry sink can use the 2", and they are 2" until they are vented; after that, the traps and trap arms are 1.5"

    You don't show them, but the laundry sink and the kitchen sink will each have a p-trap.


  8. #8
    Moderator & Master Plumber hj's Avatar
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    You would also have to be sure that that 2" stub does not have a "P" trap under the floor. To be perfectly correct, the sink vent has to tie back at least 42" above the floor.
    Licensed residential and commercial plumber

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    I would cut the cap off of the stub and put a st 90 and then a p-trap. Fill the trap with water. Have another person flush a couple toilets at the same time and maybe drain a bathtub all at the same time. I'd just check that before I went hog wild with the AAV

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    Keep in mind that an AAV will only let air in and should never let any air out. When there's a large flow in the pipes that don't have an atmospheric vent path, it's possible that it can disrupt the water in their traps and gurgle or spit some water out. If properly done, the AAV will prevent a vacuum that could suck them dry, but you could get crud spit back out of them if it gets pressurized enough.
    Jim DeBruycker
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  11. #11
    Plumber jimbo's Avatar
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    That 3" stack is a waste stack, so you could not connect any kind of vent to it in the basement. Apparently the IPC would allow the AAV. Here, we could not wet vent the laundry tub. Maybe you can under the IPC?

  12. #12
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    If that 3" stack is the building drain and he is on a septic system......and his proposed laundry sink and washer is the last fixtures on that line and theres not an atmosperic vent.

    There will be problems.

    Even if he is not on a septic system it could still cause problems.....but maybe not ALL the time,could be intermittant depending on the flow in the main sewer in the street.

  13. #13

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    Thanks for all the help thus far, sounding like this may be possible. Here is some additional information:

    on a septic system - the line at the lagoon is 4". I don't think there is a trap under the floor due to the smell still coming out after I ran some water down the stub up. This stub is likely not at the end of the line based on where the 3 inch stack and the lagoon are at (stack on west wall lagoon on northeast side of house). I am pretty certain the 3 inch stack only receives water from a double lavatory, the washing machine and another laundry sink upstairs. The stools go into a different stack. Could I use a single 2 inch trap under the sink and run straight drains from the two sinks and place the vent between the two???

  14. #14
    Retired Defense Industry Engineer jadnashua's Avatar
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    It is common to join vents to minimize penetrations through the roof, but no, generally, each sink should have its own trap AND vent. The code most places is you can join vent lines at eith 6" above the flood rim of the highest, or 42", whichever is higher. As said before, the reason for a vent is to prevent disrupting a trap when water/waste is flowing by the traip from another fixture. The goal is to keep it full so it can work, preventing sewer gasses from getting into the house. Improper venting can sometimes cause bad draining and suctioning the trap of other fixtures.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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