Horizontal wet vent question. WC midstream

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JBM

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Adding a master bath to a 3rd floor.
No shared vent from the rest of the house.
I am in Michigan
2 questions.

1. Do I need the 2" dotted line vent for the shower in the 1st attached picture? Or is it ok to wet vent to the 2" vent downstream from the WC?
2. I can also attach the WC downstream and wet vent both the shower and WC via the double lav as show in the second picture. Is this a better/worse option?

Any input is greatly appreciated
 

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wwhitney

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WetVent1.jpg: if the dry vent coming off the 3" line after the WC 3" wye is vertical until at least 6" above the WC and shower flood rims (you've drawn it horizontal below the floor, which is not allowed for a dry vent), and if the pipe run from the shower 2" p-trap to that 3x3x2 vent wye (i.e. the shower trap arm) is no more than 8' in length and 2" in total drop, then the dashed vent line is not required. The dry vent can serve as a common vent for both the shower and the WC (IPC common vent).

If, however, that would make the shower trap arm too long, then you'd need the dashed vent line, so that the shower vent takeoff occurs within the length and fall limits. But again, the dry vent needs to rise (meaning at least 45 degrees above horizontal) from the takeoff point to at least 6" above the shower curb.

WetVent2.jpg: Here the double lav wet vents the shower and then WC. Which is fine as long as the shower trap arm (from trap to shower/double lav joint) satisfies the 8' run and 2" fall limits.

Note that there is no length / fall limit for venting the WC.

Cheers, Wayne
 

JBM

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thanks wayne!
the first pic WetVent1 is considerably easier than WetVent2 considering the space constraints I am working in.
if I run a dry 2" vent line directly off the WC waste line rather than off the main waste line, does that solve the horizontal below the floor issue? and still vent the shower?
 

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wwhitney

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You can dry vent the WC and use that to wet vent the shower. But the WC dry vent still can't be horizontal under the floor.

If you don't want to use the lavs to wet vent both the WC and shower (which requires that the lavs join either the WC or the shower first, before the shower and WC join each other), then you need to dry vent either the shower or the WC, without any horizontal under floor dry vents. The typical approach would be to route the shower drain next to a wall that the vent can rise up, and then use the shower to wet vent the WC.

Cheers, Wayne
 
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