UPCHorizontal wet vent config question

[j-flux]

I have a UPC horizontal wet vent question for the attached diagram. We have a 2nd floor (no cleanouts required) renovation condition with a shower, then lav, and then a wall hung toilet. In the diagram shower is most upstream fixture, 2” line goes to 2” combi wye on its back, 2” up from there to san tee for lav (and continues as 2” vent through roof), 2” horizontal line continues from combi-wye to transition 2”x3”x3” combi-wye on back for horizontal wall hung toilet toilet and then continues as 3” waste line down to drain. I assume the 2” line off the toilet combi-wye begins the wet vent to the lav san tee. Questions are: 1. shower seems correctly vented as a dry vent, but since lav drains down that vent, i assume it’s a wet vent for shower, and is the code allowed one fixture upstream of the wet vent, and 2. Does the wall hung toilet need to enter the line with the 3” combi-wye on the flat instead of on its back/vertical? If so, why?
Thanks ahead of time for the help! This forum is incredibly helpful when the code is tricky.

 

[Reach4]

Questions are: 1. shower seems correctly vented as a dry vent, but since lav drains down that vent, i assume it’s a wet vent for shower, and is the code allowed one fixture upstream of the wet vent, and

Your drawing shows the shower wet vented, which is fine and normal. The lav is dry vented. So this is just terminology/semantics that we are discussing.

2. Does the wall hung toilet need to enter the line with the 3” combi-wye on the flat instead of on its back/vertical? If so, why?

Good question.

 

[Sponsor]

 

[wwhitney]

I have a UPC horizontal wet vent question for the attached diagram.

Diagram is UPC compliant, where the 60" shower trap arm length limit is measured to the "crotch" of the 2" wye (which is where the branch opening of the wye connects to the barrel), and the drop over that trap arm is also limited to 2" total fall.

shower seems correctly vented as a dry vent, but since lav drains down that vent, i assume it’s a wet vent for shower, and is the code allowed one fixture upstream of the wet vent

Shower is correctly vented, but it's a wet vent, as the lav drains through a portion of the vent. In your configuration, if the lav itself were deleted, it would be a correct dry vent for the shower, which then wet vents the WC.

, 2. Does the wall hung toilet need to enter the line with the 3” combi-wye on the flat instead of on its back/vertical?

Not required, as the UPC is silent on this topic. For the actual text of the requirements, see:

Chapter 9 Vents: California Plumbing Code 2025 | UpCodes

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Cheers, Wayne