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Thread: Minimum Trap Arm Length

  1. #1
    DIY Member handyman923's Avatar
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    Default Minimum Trap Arm Length

    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. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    I think I read two pipe diameters, but don't quote me on this...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Default trap

    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.
    Licensed residential and commercial plumber

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    DIY Junior Member denikar's Avatar
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  5. #5
    DIY Senior Member wjcandee's Avatar
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    Default

    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.

    http://www.klickitatcounty.org/build...andout0411.pdf

  6. #6

    Default

    our code requires a minimum of 2 pipe diam to avoid crown venting

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