How many toilets per main stack?

Discussion in 'IPC Plumbing Code Questions' started by Michael Bender, Dec 7, 2020.

  1. Michael Bender

    Michael Bender New Member

    Joined:
    Oct 22, 2020
    Location:
    Raleigh, NC
    I'm in Raleigh NC. A previous post about a bathroom I'm adding to my attic and how I plumbed it is here: https://terrylove.com/forums/index.php?threads/does-it-pass.90352/

    I've got it run all the way down to where I would tie it into the main stack and had a plumber I like who does a lot of work for me come out to fix an unrelated and issue and asked him for his thoughts on my work. He said he wouldn't help me tie it into the main stack because of to many violations. He specifically cited:

    1. Short turn 90 not allowed on drops.
    2. Only 2 bathroom units can be tied to the main stack.
    3. If you go over 3 toilets you are to upgrade the crawl drain to 4” to the 1st toilet

    He mentioned a few other items to me that make me question if he is just being overly conservative or going by rules of thumb vs. actual code so thought I'd ask your opinions.

    My house has two full bathroom groups and one half bath room on it already. I'm adding another full bathroom group to the attic. This brings the total to 3 full baths / 1 half bath.

    I vented my new bath separate from existing vents. There are two other 2" vents on the system and while I can guess, I'm not entirely sure what vents where.

    My bathroom group in the attic uses a 3" short turn 90 to fit in the floor joists to go from horizontal to vertical through a wall. Drops about 9' and uses a long sweep (maybe medium?) to go horizontal (is short allowed?) about 6'.

    I've not tied in the drain yet to existing drains, but this runs to where I can easily wye with a 45 into an existing 3" drain from one bathroom group. After my proposed wye the existing 3" drain then wyes on a vertical with the other full bathroom group 3" drain to go into the crawl space where it picks up the half bath and carries out of the house (I need to check but not sure if this is 3 or 4". Will check and report back if it matters).

    Can I really not do this?
     
  2. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    Up to three water closets on 3" horizontal.
    We go to 4" on the horizontal line when the 4th toilet is added.

    [​IMG]
     
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  4. Michael Bender

    Michael Bender New Member

    Joined:
    Oct 22, 2020
    Location:
    Raleigh, NC
    Well, it looks to me like it's 3" out of the crawl space into the yard. So you're telling me I have to replace the pipe all the way to the city tie in with 4"? Man, is there any way around this?
     
    Last edited by a moderator: Dec 7, 2020
  5. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    In Washington State they use a 4" line to the home and stub into the foundation with 3" if there are three toilets.
    You might check and it could be that there is a 4" line right outside the foundation.

    On the vertical it's not a problem.
     
  6. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    In plastic, the catalogs list "1/4 bend" which I call medium turn; "long sweep 1/4 bend" which I call long turn, and "vent 1/4 bend" which I only use if extremely space constrained on a vent. The "vent 1/4 bend" is distinguished by actually have the two hubs almost touching at the inside corner.

    For drains, horizontal to vertical can be medium turn (or a sanitary tee). Horizontal to horizontal and vertical to horizontal have to be long turn (or a wye or combo).

    Yeah, that's not a thing.

    As Terry mentioned, that's true for the IPC and the UPC--a 3" horizontal drain is only allowed to carry 3 toilets, so at the point where the 4th one comes in, you need to use 4" from there to the sewer. Usually the line outside your house is 4".

    Interestingly enough, the NSPC (used in New Jersey, not sure if anyone else uses it) allows 4 water closets on a 3" horizontal line. So in New Jersey, you'd be fine. Maybe their sewage behaves differently.

    As long as the upper 90 is not a vent 90, and the lower 90 is one size larger, that means you have a medium turn and then a long turn, which is fine.

    Cheers, Wayne
     
  7. Michael Bender

    Michael Bender New Member

    Joined:
    Oct 22, 2020
    Location:
    Raleigh, NC
    Thanks for the feedback! Very helpful indeed. You need to add a donate or buy me a beer/tea button or something.
     
  8. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    they also have an exception in seattle code that give inspector discretion to allow 4 w/c on a 3 inch line on room additions . that would be overburdening to change pipe size So if you were pulling permits and inspecting your area could have such a rule too. IM not familiar on ipc code
     

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