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Thread: Vent distance to bathroom sink

  1. #1
    DIY Junior Member wheaty's Avatar
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    Default Vent distance to bathroom sink

    We have an unfinished room in the basement that is plumbed for a 1-sink bathroom. I don't like the current position of the sink drain and would like to move it. The trouble is (I think), that its new proposed position would make the sink trap too far (more than 3' 6") from the current vent position. The drain pipe diameter is 1-1/2 inches. (Please correct me if I've misunderstood the required trap-to-vent distance).

    My question: Am I allowed to move the vent such that its connection to the drain is within the required 3' 6" of the new sink trap. Please look at the "Current" and "Proposed" diagrams below for clarification. Thanks very much for any help.
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    Test, Don't Guess! cacher_chick's Avatar
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    Under UPC, 3'6" is the max distance allowed between the trap and it's vent for 1-1/2" pipe. What you have proposed is fine as long as you are using the correct fittings and are within the max distance for the length of the pipe.

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    DIY Junior Member wheaty's Avatar
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    Quote Originally Posted by cacher_chick View Post
    Under UPC, 3'6" is the max distance allowed between the trap and it's vent for 1-1/2" pipe. What you have proposed is fine as long as you are using the correct fittings and are within the max distance for the length of the pipe.
    Thanks a lot. I very much appreciate your help. Onwards...

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    Moderator & Master Plumber hj's Avatar
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    Why are you "teeing" the vent into the horizontal pipe there, instead of at, or around, the corner?
    Licensed residential and commercial plumber

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Move the vent line, either run it straight down, or around the corner so it's within the specified distance to the trap arm of the relocated vanity. You could put a cap on the wye where it goes in now and install a new one wherever you can to get it within the specs. The issue is that with the required slope, there must be a path for air for the venting to work properly, or it's possible the pipe might be full of water because of the height differences where you tap it in. The bigger the pipe, the further away you can be at 1/4"/foot and still not potentially 'cap' the line up.
    Jim DeBruycker
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    DIY Junior Member wheaty's Avatar
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    Quote Originally Posted by hj View Post
    Why are you "teeing" the vent into the horizontal pipe there, instead of at, or around, the corner?
    I see your point. The reason I'm doing it there is that the water lines for the sink need to pop out at the corner (the cabinet is one of those Ikeas that seem to give you very little leeway on your plumbing choices) and crowd me out, and the walls are 2x4 around the corner, which complicates things there. Thanks for your input.

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    DIY Junior Member wheaty's Avatar
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    Quote Originally Posted by jadnashua View Post
    Move the vent line, either run it straight down, or around the corner so it's within the specified distance to the trap arm of the relocated vanity. You could put a cap on the wye where it goes in now and install a new one wherever you can to get it within the specs. The issue is that with the required slope, there must be a path for air for the venting to work properly, or it's possible the pipe might be full of water because of the height differences where you tap it in. The bigger the pipe, the further away you can be at 1/4"/foot and still not potentially 'cap' the line up.
    Thanks for your advice. I realise that my design may not be functionally optimal, but there are "space" reasons I can't run the vent as you suggest. I'm just double checking here, but if I do as I propose, I'm thinking I'm ok as long as I'm within the 3'6" to the trap? I'd try and get it as close as I can to the trap. Cheers.

  8. #8
    Test, Don't Guess! cacher_chick's Avatar
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    I figured there was a reason you were not going vertical closer to the trap. There is nothing wrong with your proposed installation, it's just not what we we would normally expect to see.

    The vertical vent take-off must be within 3'6" of the trap and the horizontal section of vent cannot be below 42" from the floor.

  9. #9
    DIY Junior Member wheaty's Avatar
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    Quote Originally Posted by cacher_chick View Post
    I figured there was a reason you were not going vertical closer to the trap. There is nothing wrong with your proposed installation, it's just not what we we would normally expect to see.

    The vertical vent take-off must be within 3'6" of the trap and the horizontal section of vent cannot be below 42" from the floor.
    Thanks again!

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    DIY Junior Member wheaty's Avatar
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    Last question, if I may: The fitting connecting the drain to the vent (just above the word "Proposed") should be a wye right? Or a wye combo? Or either? Thank you.

  11. #11
    Test, Don't Guess! cacher_chick's Avatar
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    A wye and an 1/8 bend or a combo, same same.

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