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Thread: Wet Vent Under Slab

  1. #1
    DIY Junior Member pkin's Avatar
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    Default Vent Under Slab

    Hello All,

    I would like to move a shower drain that is located under a slab in my home:

    I am planning to move the shower drain by removing the existing shower trap and extending the 2" line. At the new position the drain will be about 8' from the existing vent, and so I am planning to add a vent near the new drain trap. The cleanest solution for me would be to run the vent under the slab so the side of the shower before going vertical. The following pattern is given in the book "Plumbing a House" by Peter Hemp, Taunton Press, 1998. And I guess this is just wrong???
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    Last edited by pkin; 10-07-2011 at 01:32 PM. Reason: adjusted based on feedback

  2. #2
    DIY Junior Member pkin's Avatar
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    Regarding adding a cleanout upstream of the shower drain, it seems like its required, but I don't understand why a clog couldn't be removed by simply running a snake through the drain. So maybe its not required?

  3. #3
    Test, Don't Guess! cacher_chick's Avatar
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    It's apparent that you have no idea what a wet vent is.

    Here a 2" drain with 5' between the trap and vent would meet our code if it is pitched at 1/4" per foot, but YOUR plumbing code will be the determining factor.

    If your new drain line is 8 feet, you will need to re-vent it, which means coming up vertically within the minimum distance. You cannot tie the vents together below the flood rim of the highest fixture.
    Last edited by cacher_chick; 10-06-2011 at 05:20 PM.

  4. #4
    DIY Junior Member pkin's Avatar
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    Thanks for your consideration. I have 8' not 5' so I need to add a vent closer to the new trap. Can I run a vent horizontal as shown in the drawing as long as I plumb it as if it were a drain and keep the vent sloped at 1/4" per foot?

    And do I need a cleanout somewhere upstream of the shower drain if its 8'?

    Thanks

  5. #5
    Test, Don't Guess! cacher_chick's Avatar
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    NO.... You cannot run a vent horizontally anywhere below the slab! The vent must come up vertically within the minimum allowed distance.
    A cleanout for a shower will often be in the vent riser.

    Depending on the layout of the fixtures and main line, it is sometimes possible to wet vent a tub/shower through the lavatory. The only time a wet vent is permitted in a bath is through the lavatory.

  6. #6
    DIY Junior Member pkin's Avatar
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    Thanks for the help!

  7. #7
    Plumber jimbo's Avatar
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    It would only be a wet vent if another fixture...such as a sink....upstream, drained through that section of pipe.

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    Moderator & Master Plumber hj's Avatar
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    Do NOT call it a "wet vent" because the ONLY time it would be "wet" is when the shower backed up, and that would be the WORSE time for it to be wet because every time it happened, debris would enter the vent, and without something to wash it away, it could eventually close the vent. Your rudimentary drawing does NOT give us enough information to tell HOW you could install a vent properly, but I am sure the new shower is NOT 16' wide.
    Last edited by hj; 10-07-2011 at 07:37 AM.
    Licensed residential and commercial plumber

  9. #9
    DIY Junior Member pkin's Avatar
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    OK ... an actual wet vent would be allowed because debris could be washed out. Now I get it.

    And that means that the following pattern is NOT allowed
    ( from "Plumbing a House", by Peter Hemp, Taunton Press, 1998.)

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    Thanks.
    Last edited by pkin; 10-07-2011 at 01:17 PM.

  10. #10
    DIY Junior Member kentd's Avatar
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    In the book diagram, what if you were to put a cleanout on the vertical portion of the vent (above floor level)? In that case you could unclog the horizontal portion of the under slab vent via the cleanout.

  11. #11
    Forum Admin, Expert Plumber Terry's Avatar
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    The drawing shows fittings that aren't even allowed below grade.
    The 90's are vent only, to be used at least 42" above the floor.
    And the Santee on the horizontal should have been a wye fitting. Peter Hemp doesn't have much of a clue.
    I would like to see him get that passed anywhere with a plumbing inspector.

    If your shower has walls on three sides, then the wye fitting could have been used and gone up vertically in the first wall it passed.

  12. #12
    Moderator & Master Plumber hj's Avatar
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    That drawing was made by someone who actually believes "any one can be a plumber" if they just buy enough pipe and fittings to make it work. And since it is in "your own house" you do NOT need to worry about permits or inspections.
    Licensed residential and commercial plumber

  13. #13
    In the Trades Tom Sawyer's Avatar
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    The fittings are wrong and unless that "vent" is washed by a fixture above it is flat and below the flood lever rim so it's not allowed either
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  14. #14
    DIY Junior Member nepats's Avatar
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    Hi, I was wondering would the diagram be allowed under this MA code.
    (b) Vertical Rise.

    1. Where vent pipes connect to a horizontal soil or waste pipe:
    1. The vent shall be taken off above the center line of the soil or waste pipe drain.
    2. The vent pipe shall rise vertically, or at an angle of 45E from the vertical, to a point at least six inches above the flood-level rim of the fixture it is venting, before it may offset horizontally.
    2. If it is not possible or practical to vent the fixture trap as required in 10.16(7)(b)1.:
    1. A vent serving a floor drain, floor sink, or similar floor mounted fixture may be extended horizontally above the centerline of the drain of the fixture to the nearest practical location where it can rise vertically.
    2. The vent shall connect to soil or waste pipe above the centerline of the drain not less than 45E from the horizontal before running in a horizontal position.

  15. #15
    In the Trades Tom Sawyer's Avatar
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    In Mass it't gonna depend on who inspects it. Theoretically Mass does allow a flat vent but in practice most inspectors are not gonna let it fly
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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