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Thread: Trap placement question for washer standpipe

  1. #1
    DIY Junior Member mud's Avatar
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    Default Trap placement question for washer standpipe

    Happy thanksgiving, everyone.

    I am installing a new 2" clothes washer standpipe, with the trap arm expected to be about 5 ft long.

    Is it preferable to place the trap at the base of the standpipe or closer to the sanitary tee? Is there a maximum length of pipe the discharge can travel before hitting the trap?

    If I place it close to the sanitary tee, it will be easier to use the trap cleanout plug, and it will shorten the trap arm, if that's of any benefit.

    I plan to build a permanent platform for the (front load) washer & dryer, instead of buying pedestals. Will that platform become the new "floor" for determining the height of the trap? (UPC requires trap between 6" - 18" from floor.) it seems people would have to move the trap when they used pedestals then.

    The reason the trap cleanout will be easier to use is that I plan to place the trap underneath the 11" high platform, and the trap will be closer to the front of the washer, rather than having to reach all the way to the back where it would be inaccessible.

  2. #2
    Plumber jimbo's Avatar
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    That is a very interesting question about the trap height, and I do not know the anwer. The "platform" mount is a fairly recent concept which is becoming very popular. In a normal replacement situation, I am sure no one is raising the existing trap. But logic tells me that the "floor level" should be the level the machine is sitting on.

    I hope you don't mean a trap with the little cleanout plug on the bottom. Nearly useless, especially for a washing machine. If anything, you would like to have the ability to completely remove the trap for cleaning, but such is not a code requirement. You will clean from the standpipe, and there should be a nearby cleanout plug for the line.

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    DIY Junior Member mud's Avatar
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    Functionally speaking, it seems like the only thing that matters is the standpipe height itself. Too short, and it could overflow. Too long, and it could wash out the trap. Other than that, the washer's discharge hose simply has to reach, so the standpipe can't be 8 ft high. Am I missing something with the principles?

    On your suggestion, I might use a removable trap instead of the one with the 1/2" plug. It's just that our bath trap runs so slowly, I'm sure it must be full of sand from kids, and I bet a that small plug would let it out if it were there.

    Any thoughts on whether it's better to put the trap at the base if the standpipe or closer to the sanitary tee, which are about 5 ft apart? If under the platform, the trap could only be accessible when closer to the sanitary tee.

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    Test, Don't Guess! cacher_chick's Avatar
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    You cannot have a running trap- it must be at the bottom of the standpipe. You could install a wye in the trap arm for a cleanout if you thought it might be useful, but snaking a washer standpipe is very seldom a problem. If something makes it's way through the wash basket and washer pump, it's not very likely to plug the drain.

    I tend to think the height of trap issue was added to the code to make it clear that it is not supposed to be below the floor, and must be high enough to be serviceable.

    I would consider it to mean from the finished floor, as I'm sure it were intended.

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    DIY Junior Member mud's Avatar
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    Thanks for the reply, cacher_chick.

    Your reasoning for the standpipe rarely needing to be snaked and the trap height seems solid.

    I didn't know the name of the running trap until now, and I found another thread from a year ago that suggests running traps are not prohibited, but not preferred.
    http://www.terrylove.com/forums/arch...p/t-38296.html

    it would make the trap acessible to have it a running trap, but since some people install the trap inside the wall, maybe that's not an issue?
    Last edited by mud; 11-24-2011 at 01:48 PM. Reason: Damned iPhone always "correcting" my spelling to some nonsense.

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    Moderator & Master Plumber hj's Avatar
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    An "accessible" trap for a washing machine is SELDOM necessary. Any stoppage will be in the line PAST the trap, and that is where the cleanout should be. The top of the standpipe MUST be higher than the water level in the washing machine when it is filled. And the ideal standpipe length is between 18" and 30" which would establish your trap height.
    Licensed residential and commercial plumber

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    DIY Senior Member dlarrivee's Avatar
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    This is a non question, if you plan to have a 5' trap arm, how on earth do you plan to have the trap "closer" to the sanitary tee?

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    DIY Junior Member mud's Avatar
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    Quote Originally Posted by hj View Post
    An "accessible" trap for a washing machine is SELDOM necessary. Any stoppage will be in the line PAST the trap, and that is where the cleanout should be. The top of the standpipe MUST be higher than the water level in the washing machine when it is filled. And the ideal standpipe length is between 18" and 30" which would establish your trap height.
    If that's the case, then the trap height must be measured from the top of the platform or pedestal, because that's the only way to make those dimensions.

    When on a 12" pedestal or platform, a typical max fill height for my machine is 36" from the floor. However, if the machine went haywire, the overflow height is more like 52" from the floor (out the detergent dispenser). Going an inch above that with the 30" max standpipe would place the trap at 23", 5" above the 18" UPC max height from the floor, but only 11" above the platform.

    I guess what I plan to do is to place the trap at the base of the standpipe rather than make a running trap and at a height of 10" to fit under my platform, with a 30" standpipe I can add to if necessary.

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    DIY Junior Member mud's Avatar
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    Quote Originally Posted by dlarrivee View Post
    This is a non question, if you plan to have a 5' trap arm, how on earth do you plan to have the trap "closer" to the sanitary tee?
    Sorry, what I should have said is that the standpipe and sanitary tee are 5 ft apart and that I was considering placing the trap close to the sanitary tee (a running trap) instead of at the base of the standpipe.
    Last edited by mud; 11-24-2011 at 07:32 PM.

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    DIY Senior Member dlarrivee's Avatar
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    I don't see any good reason not to have the trap at the bottom of the stand pipe, that is how it is done.

  11. #11
    Moderator & Master Plumber hj's Avatar
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    I have NEVER seen a front load machine with a 36" fill height, from its base. But the distance from the floor IS based on the supposition that the machine is sitting on the floor. Front load bases were not even a consideration when the code was written.
    Licensed residential and commercial plumber

  12. #12
    DIY Junior Member mud's Avatar
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    I haven't either. Mine only reaches that height when it's sitting on a 12" platform. Otherwise, the normal max fill height is 12" lower, or about 24".

    I guess the unresolved question here is whether a pedestal or built-in platform is a "floor" for purposes of code interpretation, and something tells me I might have to wait at least one more code revision for that answer. For now, I'm going to assume the floor is what I stand on, and not what the machine stands on, even though it's the machine and not me that's regulated by the UPC.

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