3 inch to 4 inch waste line

Discussion in 'IPC Plumbing Code Questions' started by Willie Two, Feb 27, 2012.

  1. Willie Two

    Willie Two New Member

    Messages:
    36
    Location:
    British Columbia
    At what point in the house can the drainage system go from 4 inch main drain down to a 3 inch pipe ?
  2. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,236
    Location:
    Land of Cheese
    The required pipe size is determined by the number of fixture units draining into the pipe. Most common single-bath, single family homes would not require a 4" drain anywhere. Local plumbing codes may require 4" from the home to the city sewer connection.
  3. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,296
    Location:
    Yakima WA
    The way your question is worded, it sounds like you want to reduce the out going drain from 4" to 3". I hope this is how I am reading the question and not what you want to do. (sorry, I'm just an old school teacher)
  4. Willie Two

    Willie Two New Member

    Messages:
    36
    Location:
    British Columbia
    Problem solved, thanks to all who answered.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,230
    Location:
    Cave Creek, Arizona
    you do not say HOW the problem was solved, but the common answer to the original question would be "you can use 3 inch up to the point where you connect a fourth toilet. Then it has to increase to 4 inch pipe". UNLESS, you live in an area which requires the vent out the roof to be the same size, undimished, as the incoming line, then you need to run 4" all the way.
  6. Willie Two

    Willie Two New Member

    Messages:
    36
    Location:
    British Columbia
    The inspector allowed 3 inch as I only have 2 WC. Increase to 4 inch just before it leaves the building.

    Last edited by a moderator: Mar 15, 2012
  7. mikeplummer

    mikeplummer Plumber

    Messages:
    190
    Location:
    Ontario, Canada
    by code you should be 4" building drain to your 3" stack which remains 3" all the way to open air
    2 toilets on 3" if horizontal, 4" downstream of 3rd
    3" stack can be up to 6 toilets, after six must be 4" pipe
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