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Old 05-24-2011, 02:57 PM   #1
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standpipe trap location


my main stack comes down thru my utility room wall, drops into my crawl space, does a 90 deg turn where it then runs horizontal about 5 ' or so, over to the main drain, then 90 deg down and ties into the main drain. So I end up with a short (approx 5 ft) horizontal stack offset that's right up under the floor joists.

There's an existing 2" wye off this stack offset - I had an extra 2"x3" fitting when I ran the offset so I stuck it in there and just capped the 2" part for future reference - figured it couldn't hurt (otherwise it would end up in the pile of spare parts).

Now I'm looking at a temporary setup for a washer / dryer in the utility room - until I get to fixing up the actual laundry room later (probably much later). Is there any issue with dropping a washer standpipe straight down thru the floor, putting a p-trap under the floor joists, and connecting the trap arm laterally to that "spare" 2" stub?

Rather than cut the stack, add a tee, drill thru a couple studs, etc. to get the trap in the wall, I'm thinking I'll just do the above. Seems like this isn't really much different from a shower trap (under the floor) but the distance from the top of the standpipe to the trap down below is what I'm not sure of - is there a vertical / height restriction related to flow into p-traps?

Related question - can I run a hose from my hot water tank pressure release into the standpipe as well? Using a drain fitting - maybe like the ones for a dishwasher - put it right in the standpipe..?

thanks

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Old 05-24-2011, 03:45 PM   #2
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standpipe trap location


that would work but you would need to put another wye or tee between the trap and the main and vent it which probably would be easy to do. if its just temporary you might just run the vent up in the tem laundry room behind the washer and use one of those mechanical vents they make. we used to call them quicky vents they call them automatic vents nowadays. If you dont vent it the water could get sucked out of the trap possibly when flushing toilets.

http://www.plumbingsupply.com/autovent.html

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Old 05-24-2011, 03:58 PM   #3
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standpipe trap location


thanks DannyT - another question - the distance from the trap to the existing 2" wye / stub (at the stack offset) would only be about a foot or so - so the trap arm would be very short. Does that make any difference re: the additional vent requirement?

thanks

Last edited by rtoni; 05-24-2011 at 04:15 PM.
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Old 05-25-2011, 06:04 AM   #4
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standpipe trap location


not a bit. in most locations the vent needs to be within 6 feet of the fixture depending on what you are venting. i would run the standpipe up at least 36 inches above the floor
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Old 05-26-2011, 12:19 PM   #5
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standpipe trap location


thanks again Danny - appreciate the feedback...
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Old 05-29-2012, 11:27 AM   #6
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standpipe trap location


hi - resurrecting this thread to ask another related question. I'm finally getting to hooking up the washer box in this room (yes it's been another interesting year). Anyway, as I'm working with the 2" p-trap and connections, I realize I can just fit the trap in the wall if I offset the standpipe with a couple of 45's to bring it over against the stud on one side of the wall cavity. I can drop the offset pipe straight down into the trap inlet, with the trap outlet then turning 90 down right beside the stud on the other side, and straight down thru the floor - there's just enough room to do this. It keeps the trap in the wall, above the floor, and I can still use the existing wye in the crawl space to tie into the main drain.

Is there any issue with offsetting a washer standpipe this way? Or is it a problem not having the trap accessible e.g for the cleanout, should I decide to cover the walls in the utility room?
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Old 05-30-2012, 12:05 PM   #7
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standpipe trap location


that will work better if you use a tee instead of a 90 on the other side of the stud and run the pipe up higher then the washer drain and use an AAV (air admittance valve) on top. i used to offset the riser the same way to make it fit in a stud space.
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Old 05-30-2012, 03:12 PM   #8
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standpipe trap location


Thanks again DannyT. Can I assume it's OK to have the AAV hidden behind drywall, if I cover this over later..?

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