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[SkullMesaRanch]

deleted

 

 

[ACADuser]

Look up "wet vent"

 

[ACADuser]

The blue line is a wet vent

https://www.pmmag.com/articles/102031-we-might-get-letters-a-horizontal-wet-venting-leap-of-faith

 

[DrawingABlank]

You could just plan to vent them separately until they can reconnect in the attic or in this case the floor system.

[Bob-Roraback]

Good relevant article

JLC Online Article PDF_ 0915b_JLC_CEV_L.pdf.pdf

[ACADuser]

If you need to run the Arm 8' use a 2" arm. You can still use a 1.5" trap. You have to measure from the weir.

If you need less than 5' of arm use 1.5" pipe.

 

Make the wall thicker if the 1.5" arm is a structural issue.

 

If that doesn't work for you some jurisdictions allow an "Auto Vent" to be used inside the vanity.

This is how I would layout the piping.

 

[ACADuser]

If you put the stack directly behind the lavatory you often conflict the vent stack with the light electrical box above the vanity.

So you have a very short arm or the have to offset the stack pipe below the light fixture.

[DrawingABlank]

54 minutes ago, SkullMesaRanch said:

 

Would that also be better than routing a drain vent horizontally under the window (going thru king studs)?

Looks like due to the height of the window the horizontal vent under the window will not work. The vent needs to raise above the sink 'full line' before moving horizontal. (Limits 'dirty vent' should sink ever plug up.)

 

Sure there are a few more fittings and a stick of 1.5" but that is the trade off sometimes for design preferences. I would vent the sink by itself up into floor system before trying to tie it to a 3" vent in an exterior wall. (harder to insulate properly)

 

Alan has a good reminder on keeping clear of other needed MEP in the wall.