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Thread: New Washer Standpipe Connection?

  1. #1

    Default New Washer Standpipe Connection?

    I'm adding a stackable washer/dryer in closet behind my bathroom and have limited space and old cast iron piping from 1949 to work with. I'm attempting to be as descriptive as possible and have also attached some photos.

    Photo 1 -- in the basement there 2" line that I can tap into and immediately adjacent (< 6 inches away) ia a 1.5" line that feeds a lavatory sink and then vents to the roof (the vent is also 1.5"). Both of these lines drop through the floor ~1 foot and then runs ~6 feet before they join the main waste stack.

    Question 1: Can I use the 1.5" line from the lavatory as a wet vent? If I understand correctly a vertical 1.5" wet vent can support 4 fixture units and I'm less than the critical distance (as my trap will be < 2 feet away). Am I correct?

    Photo 2 -- on the top side ... I've got what I think is an S-trap and need some suggestions. Working from the bottom of the picture upwards.

    The 2" line comes up through the floor via a 1/8 fitting ... goes ~ 1 foot to another 1/8 fitting. My P-trap ties into this via a 1/4 elbow. The wier of the P-trap is 16" off the foor and the standpipe extend 24" up. See illustration below.

    ......................|| (standpipe)
    ......................||
    ..(1/4 b).//.\\..|| (p-trap)
    ...........//...\\//
    (1/8 b)..\
    .............\-------\ (1/8 b -- segment is sloped at 45 degrees)
    .........................| (waste drops through floor)

    Question 2: Is the above an S-trap? If so, there anything that I can do in the 16" between studs that I can work with? I could also come out perpendicular to the wall and have maybe 2' to work with.

    Your thoughts, comments, and questions are welcome. -- Silicon Valley Guy (SV_Guy)
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  2. #2
    Commercial Plumber markts30's Avatar
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    Quote Originally Posted by sv_guy

    Question 1: Can I use the 1.5" line from the lavatory as a wet vent? If I understand correctly a vertical 1.5" wet vent can support 4 fixture units and I'm less than the critical distance (as my trap will be < 2 feet away). Am I correct?
    (SV_Guy)
    You have to vent the 2" separately...
    The vent should be placed at the junction between the trap arm and riser...
    (replace the 1/4 bend with a santee and the vent will work.)

    This will also cure the S-Trap issue you do have

    After putting in the santee, you can tie the vent into the 1-1/2" vent from the lav once it is at least 6" above the flood rim of that fixture...(we generally aim for about 42" for re-venting)

  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    I would vent the washer by itself,

  4. #4

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    Quote Originally Posted by markts30
    You have to vent the 2" separately...
    The vent should be placed at the junction between the trap arm and riser...
    (replace the 1/4 bend with a santee and the vent will work.)

    After putting in the santee, you can tie the vent into the 1-1/2" vent from the lav once it is at least 6" above the flood rim of that fixture...(we generally aim for about 42" for re-venting)
    Mark .. thanks for the feedback. I've swung the whole connection around to be perpendicular to the wall and will tie into the 1-1/2" vent above the lavatory in the diagonal segment. Unfortunately the highest point where I can tie into the vent is at 34" (not 42" as that would route me through an electrical box) ... this is only a couple of inches above the sink flood level. I plan to slope the vent as a drain in case water ever gets up there. I think this be OK.

    Now I have to figure out how to reset the cast iron pipe coming out of the lavatory santee as it's a bit loose. Forum searching here I come.

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