New Build in Michigan - Something doesn't look right

Discussion in 'UPC Plumbing Code Questions' started by CanadaGuy, Mar 3, 2021.

  1. CanadaGuy

    CanadaGuy New Member

    Joined:
    Mar 3, 2021
    Location:
    Michigan
    The image below is a view from the first floor of the 2nd floor bath drain and supply system that sits in roughly the center of the upper floor.

    We're building a new home in Canton, MI, and the plumbing was just roughed in by the plumber, but this drain arrangement looks odd to me.

    Let's assume first that the drain from the Toilet is actually sloped 1/4" per foot (I have to go back with a ladder to check it). That horizontal run continues off the image for another 16ft before it comes to the soil stack at the outer wall of the house.

    But, my main issue is the way they tied the Tub and Sink into the toilet. It seems to me that the Wye they put in should attach such that the tub and sink enter from the TOP of the drain line, not the side. With such a long drain across the house to the stack, I am concerned about waste in the toilet backflowing into the smaller pipes leading back to the sink and tub.

    Also, not shown above the floor: The sink is vented in a wall, so I would imagine this makes a "wet vent" for the system--is that right?

    Lastly, the entire system they put in has ONE pipe sticking out of the roof of the 2nd floor. I saw a 4" pipe through the attic to outside, but it immediately is reduced to about a 2" pipe, which then splits off all over the house horizontally to all the rooms needing venting. There is no 4" continuous stack from the basement up to the roof. After the pipes get up from the basement to the first floor, they get smaller and continue up to the attic to join this "manifold" in the attic before popping through the roof.

    Any comments would help as you never know how well the city inspector looks at some of these things before signing off.

    LoftBath_PlumbingUnderFloor_2 - Copy.jpg
     
    Last edited: Mar 3, 2021
  2. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    That is a wet vented bathroom. The discharge from the toilet is going downstream and since it goes past a wye, it keeps on going. I don't see a problem for the tub or the lav.

    A bathroom takes a 2" vent in most codes and things like a kitchen sink or washer will have a 1.5" vent.
    Those can tie together in the attic before going through the roof.
    Where I'm at, a three bath home needs a 3" vent or the composite area of a three by combining smaller pipes.
    A four bath home gets a 4" vent. In places where there is a worry about frost, they will increase the size of a 3" vent to a larger size.
     
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  4. CanadaGuy

    CanadaGuy New Member

    Joined:
    Mar 3, 2021
    Location:
    Michigan
    Thanks for the input, Terry. Shouldn't the drain from the sink line connect in to the soil line from above? Seems like coming in from the side is weird.
     
  5. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    The side is fine. You're dropping through a 2" trapway into a 3" pipe that is like having two 2" pipes and an 1-1/2" pipe in volume.
     
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