Hello, I am building a 3 level home that has a bathroom on each floor, and a laundry room on the 2nd floor that is against the bathroom wall. So I have my 6" wet wall that goes from basement to the top floor so that I could cluster all of my fixtures. My question is, since all of my fixtures are within the allowable trap arm length of the 3" vertical waste/vent stack, will I still need to provide auxiliary venting, and if so, will it have to go through the roof or can it tie back into the 3" stack before it penetrates the roof? Any help would be greatly appreciated.

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since all of my fixtures are within the allowable trap arm length of the 3" vertical waste/vent stack, will I still need to provide auxiliary venting, and if so,

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If I understand your question you're asking g to simply run all traps into the 3"vent srtack? Correct? That's going to work for the vanityn and washer. Now, we3hyat about the tub/shower? If wet vents are allowed in your area This is the way I'd lay out then bathrooms,(see image)

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will it have to go through the roof or can it tie back into the 3" stack before it penetrates the roof?

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This is called "reventing" and is acceptable. Just maintain slope back to the fixtures they're venting. Good luck, Tom

Thank you, Tom. The way I have things arranged, the Tub/Shower and Toilets are within the trap arm length guidelines in my Codecheck book. But in another section, it says toilets cannot discharge into a waste/vent stack if I am understanding it right. I do not have to meet any codes, but I want to do it right and have it work.

What's your code say about wet vents? Because you're wet venting everything abovfe the bottom fixture, Also code will not allow you to discharge a major fixture past a unvented minorv one. Have you run this by the Plunbing Inspector? Can you draw me a diagram of howi this will go down? Back to you, Tom