Single to double vanity drain & vent

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DougC

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Per the attached picture, I’d like to put in a double vanity sink about where the red spot is and hook up to existing plumbing. I see other examples but I just want to use my exact situation. Can I just tie into existing horizontal, run the second line lower over to the existing Drain/Vent line (blue line) or do I need to add a vent line up to 42” and over to existing? Any help is greatly appreciated.
DougC

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Terry

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You could install a 2x1.5 santee below the other one, run the trap arm out and just have it at that height.
That would be one lav wet venting a second lav.
Both arms come out at the 2% grade.

Two santees, two trap arms, two traps, but one high and one just below.

That being said, I'm allowed 42" on a trap arm to the vent. You might need to add venting for the upper one.
 

wwhitney

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That being said, I'm allowed 42" on a trap arm to the vent. You might need to add venting for the upper one.
The IPC allows maximum length trap arms based on the trap weir rule an 1/4" per foot drop--i.e. if the 1-1/2" trap arm has exactly 1/4" per foot drop, it can be up to 6' long.

The IPC also allows common venting, where two trap arms share a single dry vent, and the trap arms can combine before the common vent. So it would allow a horizontal 1-1/2" combo to be installed on the existing trap arm to add a second lav trap.

Cheers, Wayne
 
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