How is trap arm distance measured when the connections have bells?

[TheOverThinker]

UPC says minimum trap arm twice the pipe diameter for a laundry.
But exactly where should that be measured from?

Or put another way, should I report this as zero inches of trap arm, or 1 inch.....

Here I was the inspector, if I go back after correction what else should I check for (other than the trap arm, and vent size)?

 

[wwhitney]

UPC says minimum trap arm twice the pipe diameter for a laundry.

Right, so your second diagram is incorrect, for a 2" trap it would be 4" minimum, not 6" minimum. Also, I'm not really clear on why the plumbing codes have this "crown vent" rule that provides a minimum trap arm length. Any thoughts?

But exactly where should that be measured from?

Between the trap weir (the point where water will first spill out of the trap u-bend if you slowly add water to it) and the inside face of the vent. So between the orange lines in my mark up below.

So the full length of the hubs count as part of the trap arm. The upshot is that if you measure between the hubs, the exposed pipe needs to be about 1.75" minimum. That's from memory, there's an older thread on this site where Reach4 and I calculate it.

Cheers, Wayne

 

[Sponsor]

 

[wwhitney]

P.S. UPC 1002.2 "Each fixture trap shall have a protecting vent so located that the developed length of the trap arm from the trap weir to the inner edge of the vent shall be within the distance given in Table 1002.2 but in no case less than two times the diameter of the trap arm."

Cheers, Wayne

 

[TheOverThinker]

Right, so your second diagram is incorrect, for a 2" trap it would be 4" minimum, not 6" minimum.
Cheers, Wayne

Cool thanks, that's what I get for googling a random plumbing code picture.

Is there any (serious) concern with the apparent 1.5" vent for the 2" laundry drain?

 

[wwhitney]

Is there any (serious) concern with the apparent 1.5" vent for the 2" laundry drain?

No, it's compliant for the UPC and every other plumbing code I've looked at. For the the UPC, see Table 703.2.

One other rule that is unlikely to be an issue is that the UPC requires the total vent area through the roof to be at least as large as the minimum allowable building drain size. For houses without a large number of WC (up to 6 is OK for the 2024 UPC), that minimum allowable building drain size is 3". In which case you can meet the vent area through the roof requirement with: one 3" vent or (2) 2" vents and (1) 1.5" vent. (1) 2" vent and (2) 1.5" vents is not quite enough [1.5^2 + 1.5^2 + 2^2 = 8.5 < 9 = 3^2].

So in the unlikely event that the DWV system overall doesn't meet that rule, some of the solutions would involve upsizing the vent shown in your picture. Just mentioning this as you are an overthinker.

Cheers, Wayne

 

[GReynolds929]

FYI the washer box is crooked AF. If you installed that get a level and remount it level. If your plumber installed it he needs to come back and remount it level. There may be a need to shorten the water lines to get it level and plumber

 

[Jeff H Young]

FYI the washer box is crooked AF. If you installed that get a level and remount it level. If your plumber installed it he needs to come back and remount it level. There may be a need to shorten the water lines to get it level and plumber

Its looking Rough