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Thread: Horizontal vent question

  1. #1

    Default Horizontal vent question

    I want to use a common drain for a tub and a shower. The most convenient point to tie the two drains together (each has its own trap) is in the center of the bathroom and I would install a single vent connection just before the two drains join. That would necessitate running the vent horizontally about 10 feet to reach a wall and then turning the vent vertical and taking it through the roof. The horizontal portion of the vent would maintain a 1/4" per foot slope. The IRC applies and the installation is in a one story house.

    A schematic of the proposed piping is available on
    http://s253.photobucket.com/albums/hh75/nculbertyh/
    The santee used for the vent connection would be installed with the vent branch in the vertical position.

    Is there a limit to how long the horizontal portion of the vent can be?

  2. #2
    Plumber jimbo's Avatar
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    A vent can NOT run horizontal at all until it is 42" above the floor, or 6" above the flood rim of all the fixtures. It must come off the drain via a wye rolled to 45 and continue not less than 45 upward, until the 42" height is reached.

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    Forum Admin, Expert Plumber Terry's Avatar
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    The tub should be vented too, and the two vents tied together above the 42" level.
    Or at the least, 6" above the top of the tub.

    Like Jimbo mentioned, the vents need to be rolled above the flow line of the pipes.

  4. #4

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    OK, but this is very confusing. Below is a link to a Figure out of the 2003 IRC. Except for the lavatory (which I don't haave) the example looks just like what I want to do. If it is OK in the IRC example, why wouldn't my proposal work?

    Link: http://i253.photobucket.com/albums/h...athTubvent.jpg

    Thanks for your help.

  5. #5
    DIY Senior Member seaneys's Avatar
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    Quote Originally Posted by jimbo View Post
    A vent can NOT run horizontal at all until it is 42" above the floor, or 6" above the flood rim of all the fixtures. It must come off the drain via a wye rolled to 45 and continue not less than 45 upward, until the 42" height is reached.
    I must be missing something. How would you vent any floor drains that are next to a wall (say a shower drain that is centered in a 40x48 shower)? Wouldn't you have to run horizontal for a few feet until you can shoot up into the wall?

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    Plumber jimbo's Avatar
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    Quote Originally Posted by seaneys View Post
    I must be missing something. How would you vent any floor drains that are next to a wall (say a shower drain that is centered in a 40x48 shower)? Wouldn't you have to run horizontal for a few feet until you can shoot up into the wall?
    The trap arm runs horizontal, typically to a vertical tee, and the vent comes off vertical. If the vent must be taken off a horizonal pipe, it is done with a wye rolled to a 45 and the vent pipe must rise at least at 45 until it is above the flood rim of fixtures.

  7. #7
    DIY Senior Member seaneys's Avatar
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    Quote Originally Posted by jimbo View Post
    The trap arm runs horizontal, typically to a vertical tee, and the vent comes off vertical. If the vent must be taken off a horizonal pipe, it is done with a wye rolled to a 45 and the vent pipe must rise at least at 45 until it is above the flood rim of fixtures.
    Argh....

    Illinois Plumbing Code:

    b) Vertical Rise. Where vent pipes connect to a horizontal soil or waste pipe, the vent shall be taken off above the center line of the soil or waste pipe, and the vent pipe shall rise vertically, or at an angle not more than 45 degrees from the vertical before offsetting horizontally or before connecting to the branch vent. (See Appendix K: Illustration G.)

  8. #8
    DIY Senior Member seaneys's Avatar
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    Quote Originally Posted by Terry View Post
    The tub should be vented too, and the two vents tied together above the 42" level.
    Or at the least, 6" above the top of the tub.

    Like Jimbo mentioned, the vents need to be rolled above the flow line of the pipes.
    If you are draining into a horizontal line, could the vent be taken off upstream of where the trap arm connects?

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