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Thread: S trap question

  1. #1

    Default S trap question

    I am always coming across a lot of posts on S traps. I was reading the NJ code (national standard plumbing code) on something else and came across this under Prohibited traps......S traps of uniform internal dimensions.
    Later in the venting section it referred to "vents may be connected below the top weir of the fixture trap if the following conditions are met
    1. vertical section of drain pipe is at least one size larger than trap inlet size.
    2. the horizontal pipe connected to the trap outlet shall be at least 2 pipe diameters long.
    3. The developed length of the trap arm shall not exceed the normal table.

    Does that sound like a somewhat modified s trap is allowed?

    Also came across the requirement that a 1/1/2' drain is suitable for a shower stall served by one shower head, 2" if multiple heads.

    This is the 2006 code taken from the NJ state website.

  2. #2
    DIY Member Zenman's Avatar
    Join Date
    Nov 2004
    New Jersey


    I don't have an answer to your question, but see you said you are going by "NJ code (national standard plumbing code)". I'm a DIYer in NJ and did some work years ago (2002-2003) and my town told me to go by UPC. Now I'm starting work again (new bathroom)... I assume I'm still under the UPC. Of course I think each town could supersede the states requirements. Since you brought this up, I'm going to double check with my town and see which code they will be inspecting me on this time.

  3. #3


    My town isn't very strict. I asked about codes, especially any special codes and they said they had none, just the states. On one project that I got a plumbing and electrical inspection on they hardly looked at anything, one of them didn't even go up the stairs to see work on the second floor, he asked one question and handed me an approved sticker. It was a large complicated project and included an Ac compressor and AH to serve the addition and they didn't even look at the breaker box connections
    I certainly want to and try to insure that I meet any codes but I have to rely on myself and my understanding as they aren't even helpful with a planning question. Either way (planning or inspection) I can't rely on them.

  4. #4
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    San Diego


    After the recent news, it sounds like a couple of bucks would solve your inspector problem in New Jersey!

    Couldn't resist that.

  5. #5
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default inspection

    From the previous post, it appears you do not even need a couple of bucks. That code provision does appear to have been created to allow "S" traps by installers who cannot figure out the right way to do it, but that does not mean it is a proper way, although in MOST situations it should work. In fact, the longer the horizontal branch is before dropping vertical, the less likely it is to cause problems.


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