Wet vent code help, please!

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Donny H

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Hello all,

I'm building a new bathroom in my house on a homeowner's permit. I'm planning to use a wet vent with a lavatory, bath tub, then toilet, in that order from upstream to downstream. So the vent will come up through the ceiling in the wall behind the lavatory. I was planning to use the configuration in the image attached, with 1 1/2" pipe coming from the lavatory, until the tub joins the wet vent, then moving up to 2".

I'm confused because I had a consult with the plumbing inspector and he said I need to come up through the floor with a 2" pipe. That doesn't match anything I can find in the code book. Any ideas?

I don't want to move up to the 2" size, because that would be too large of a hole in the base plate of 2x4 wall that the sink is against and the vent comes through.

Thanks for any help!!
 

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Plumber01

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Simply put, a toilet requires a 2" vent. Your inspector is right, it should be 2" all the way up.

What code book are you referencing?
 

Donny H

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This is out of the 2018 IPC . It shows a lot of 1 1/2" stacks on systems with wet vents and water closets. This is confusing me.
 

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Stuff

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You may be technically OK with 1 1/2" between lav and tub with the IPC but, as mentioned, it is all about how the inspector interprets the code. IPC book is that 1 1/2" is fine for the overall common vent as long as final drain is 3" even with a toilet. Wet vent size is "based on the fixture unit discharge to the wet vent" - question for inspector is do you count all fixtures or only the fixtures discharging into that segment. Then the wet vent portion with only a lav discharge is OK for 1 1/2" which you can see in the upper left drawing.

Also - might be local rules that require more than the IPC.
 
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