Too tall standpipe, siphoning possible?

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Gslenk

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In comparing codes, 2018 IPC, which states minimum 18", max 42", no mention of p-trap height.
UPC states 18" min, 30" max, AND the trap is 6-18" off of the finished floor.

Is there any practical consideration if you are in an IPC area (up to 42" standpipe height)?

I like the longer pipe for reducing overflow risk, but has anyone ever had siphoning problems as the length approaches 42"? This would be for 2" pipe.

My configuration is looking to be around 36" of standpipe sticking out of the p-trap, and I'm on IPC (not UPC), so while it is allowed, I am just wondering if it is a bad idea to exceed the 30" height that other (UPC) jurisdictions use.
 

Tuttles Revenge

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Its probably a rule that has never been really engineered, tested and verified. Its just a rule that has been copied and followed for sake of tradition.

I've never seen or heard of a clothes washer trap siphoning from the stand pipe height. Modern clothes washers operate much differently than they did 60yrs ago or however when those requirements were instituted. Either rule apparently works, so I would suggest compliance with the code you're under and to the max height you feel comfortable with.
 

Reach4

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Bannerman

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For siphoning to occur, would require suction downstream of the trap. Venting requirements downstream of each trap are to prevent suction to ensure water will not be siphoned out from the trap.
 

Gslenk

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It's vented so nothing downstream could cause suction. And I was probably just overthinking it when I saw the 30" height limit elsewhere.

I have an OLD maytag top loader I'll test it with for fun. Should outflow anything remotely modern. Thanks!
 

Jeff H Young

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Its probably a rule that has never been really engineered, tested and verified. Its just a rule that has been copied and followed for sake of tradition.

I've never seen or heard of a clothes washer trap siphoning from the stand pipe height. Modern clothes washers operate much differently than they did 60yrs ago or however when those requirements were instituted. Either rule apparently works, so I would suggest compliance with the code you're under and to the max height you feel comfortable with.
I like the answer! These stand pipe rules do get strict scrutiny from a few inspectors , plumbing foreman or someone with a tape measure in their hand . but its pretty much nit picking never the less we stride to follow code 94.44 percent the time or better
 

Terry

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For a long time washers were plumbed with a 1.5" standpipe. When new they worked just fine. I had a small starter home at one point, and I had plumbed a 1.5 drain for my washer as the existing piping was that size already. It worked just fine. Older homes had those in galvanized and eventually the pipe would get smaller with age.

When I was doing a lot of new construction I would put the top of the box at 48" above the floor and the trap arm was about 9" to 12" off the floor. That gave me something like a 28" standpipe in 2".
 

Jeff H Young

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For a long time washers were plumbed with a 1.5" standpipe. When new they worked just fine. I had a small starter home at one point, and I had plumbed a 1.5 drain for my washer as the existing piping was that size already. It worked just fine. Older homes had those in galvanized and eventually the pipe would get smaller with age.

When I was doing a lot of new construction I would put the top of the box at 48" above the floor and the trap arm was about 9" to 12" off the floor. That gave me something like a 28" standpipe in 2".

Kitchens were 1 1/2 as well but now I don't run 1 1/2 for anything just trap arms except in rare cases where hole sizes or space is critical.
I don't think they set boxes at 48 around here anymore . I like seeing the connections but most jobs like em low now. Actually I'm in a minority I like the hosebibs on the wall visible and changeable
 
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