How much can I push/pull on ABS pipe to achieve slope?

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tanjs

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I am moving some shower/toilet/vent lines under my basement slab to suit the new bathroom fixture locations. I want to make sure things are all good before closing it back up.

I have run the new ABS lines (2" for shower and wet vent) and in order to achieve the proper slope (1/4" per foot) I need to push the trap arms down a bit to avoid having too much slope. Is this sort of thing ok? or is it bad to have any stress on the ABS connections?

My understanding based on NPC of Canada is trap arms must not have more fall than the ID of the pipe, other than that, "nominally horizontal" drain lines is anything between horizontal and 45 degrees and should be ok. If this is the case, my current setup with more than 1/4" per foot slope should be fine.

Any thoughts? Thanks!
 

Terry

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Standard slope is 1/4" per foot or 2%
Venting is setup to prevent a siphon of the trap, so too much slope over distance is not good. How close is the venting?
 

tanjs

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below slab.jpg

Hi thanks for the response.

The wet vent leg before the wye is quite short; approximately 12-18". I am not there to measure at the moment.
 

wwhitney

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Trap arm fall constraints do not apply to a WC, just to fixtures with external traps.

And yes, the trap weir rule restricts the fall from trap outlet to vent connection (wet or dry) to 1 pipe diameter. If the trap arm is short you can have extra slope above 1/4" per foot, as long as the total fall is compliant.

Cheers, Wayne
 

tanjs

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Trap arm fall constraints do not apply to a WC, just to fixtures with external traps.

And yes, the trap weir rule restricts the fall from trap outlet to vent connection (wet or dry) to 1 pipe diameter. If the trap arm is short you can have extra slope above 1/4" per foot, as long as the total fall is compliant.

Cheers, Wayne
Thanks for this explanation.

For the length of pipe between the wye and the vertical portion of the wet vent, is it ok to have more than 1/4" / foot of slope, as long as the fall is less than 1 pipe diameter? Or since this is not a trap arm, is there no such restriction?
 

wwhitney

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The horizontal wet vent typically has no fall limit, beyond being horizontal. Some more exotic types of venting through horizontal drains, such as circuit venting and combination waste and vent, do have a maximum rate of fall, I recall seeing 1" per foot. But I don't think that would apply to you, although I'm not familiar with Canadian codes.

Cheers, Wayne
 

tanjs

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The horizontal wet vent typically has no fall limit, beyond being horizontal. Some more exotic types of venting through horizontal drains, such as circuit venting and combination waste and vent, do have a maximum rate of fall, I recall seeing 1" per foot. But I don't think that would apply to you, although I'm not familiar with Canadian codes.

Cheers, Wayne
Thanks Wayne.

Regarding the other portion of my question, is it acceptable practice to slightly "tune" the slope by applying minor lifting/holding down of ABS pipe? Or is any stress at a connection a bad idea?

Basically, i can achieve 1/4" foot everyone if I hold down the 2" shower trap very lightly, and then also hold down the 2" seciton upstream of the wye going to the vertical.

I could rebuild it if needed; however if it doesn't need to be a piano, id rather not make it one.
 

wwhitney

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My practice, from doing only 2.5 houses worth of DWV, would be that a deflection I could achieve with moderate hand pressure, and then securing the pipe, is fine. No idea if there's any standard or if others would agree with me.

Cheers, Wayne
 

RobbyDog

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Thanks Wayne.

Regarding the other portion of my question, is it acceptable practice to slightly "tune" the slope by applying minor lifting/holding down of ABS pipe? Or is any stress at a connection a bad idea?

Basically, i can achieve 1/4" foot everyone if I hold down the 2" shower trap very lightly, and then also hold down the 2" seciton upstream of the wye going to the vertical.

I could rebuild it if needed; however if it doesn't need to be a piano, id rather not make it one.
A bit of strain on ABS isn’t going to hurt anything.
 
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