Minimum Trap Arm Length

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by handyman923, May 30, 2013.

  1. handyman923

    handyman923 Member

    Nov 20, 2006
    Portland, OR
    Is there a minimum trap arm length for a washer stand pipe? Right now, I have the outlet from the P-trap butting tight to the sanitary tee. Is this too close? Will this create a S trap?

    Thanks for any advice!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    I think I read two pipe diameters, but don't quote me on this...
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    Depending on how you measure the trap arm, the two fittings may "force" it to be at least two diameters between the "pipes". IF you have a proper vent you cannot "create" an "S" trap as long as the maximum length is within the parameters for the pipe size.
  5. denikar

    denikar New Member

    Feb 8, 2013
    Canton, MI
  6. wjcandee

    wjcandee Wise One

    Apr 27, 2012
    New York, NY
    The third page of this pdf has a diagram and a table that may be helpful. You measure, according to it, from the interior portion of the vertical pipe on the p-trap (the weir is where it tips over to the horizontal) TO the closest portion of the vent pipe. The top right diagram on the third page of the document makes it clearer. 3" pipe has a minimum 6" trap arm.
    Last edited by a moderator: Jan 24, 2017
  7. mikeplummer

    mikeplummer Plumber

    Mar 28, 2012
    Ontario, Canada
    our code requires a minimum of 2 pipe diam to avoid crown venting
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