Horizontal Vent Question

[Brian E Sasser]

Can I tie in the 2 inch horizontal shower drain line to the adjacent 3 inch horizontal wet vent using a horizontal 1 1/4 inch line (marked in blue) to vent shower trap?

Here is a sketch

Or

Is this even needed if I can control my trap arm pitch to the elbow?

 

[Terry]

As drawn, the shower isn't vented.
If you use a combo and pick up the shower off the lav line, then the shower is wet vented by the lav.
The 3" must be a vent above the lav, with no waste coming down from above. The trap arm for the lav is a santee.

 

[Sponsor]

 

[hj]

All you have done is provide a "secondary drain" for the shower if it gets plugged up past the tee connection. It is not a vent. No combination Y-1/8 bend for the lavatory connection.

 

[Brian E Sasser]

Thank you for clarification on the Santee.

Yes. The three inch above lav is a dry vent to the roof, no waste.

I switched from tub to shower, that increased drain size from 1 1/2 to 2 inch. Since the joists (2x8) are in between the horizontal runs, I am forced to go parallel to them. Old 1 1/2 inch tub drain went through and tied into the 3 inch line wet vented by the lav.

I don't do a lot of horizonal vents.

Are both ends of the blue vent combos?

 

[Brian E Sasser]

All you have done is provide a "secondary drain" for the shower if it gets plugged up past the tee connection. It is not a vent. No combination Y-1/8 bend for the lavatory connection.

Wouldn't that be dictated by the direction of the combo in the 2 inch drain line?