looking for code section to reference

[newhomeowner2017]

Hi all,
New to this forum and hoping to get some support in a disagreement I'm having with my plumber. We are remodeling an upstairs bathroom which entails moving the laundry upstairs and reconfiguring the existing shower. Plumber has completed his first day of work and has the drains laid out such that the shower would wet vent through the washing machine drain. I'm fairly certain this isn't allowed, and think I understand why (high volume of washing machine drain flow could siphon away the shower trap seal and create odor issues).

He has sent me the attached, but I don't believe this applies as the washing machine is an appliance, not a bathroom fixture. What I'm hoping for is 1) confirmation that my understanding is correct, and 2) a specific section or sections in the code that I can't point the plumber to so that he's compelled to fix this. Project is in Marin County, CA.

Any advice is greatly appreciated.

 

[Cool Blue Harley]

In California, wet venting is limited to vertical drainage piping receiving the discharge from the trap arm of one and two fixture unit fixtures.

Your clothes washer is calculated at three drainage fixture units and therefor cannot empty into your shower vent.

California Plumbing Code section 908.1.

Your interpretation of a clothes washer being an appliance and therefor not a plumbing fixture is incorrect.