canadian plumbing code

Hi everyone, I need your help. I don't really know how to explain the problem and my first language is French, please be indulgent. :) I live in Quebec. My house is the first unit of a 3 unit townhouse. My two neighbor's plumbing vent are hooked on my stack vent. (please see illustration...

Looking through the NPC 2020, it specifically states that short radius 90's cannot be used to connect 2 drainage pipes except in 2 very specific circumstances: "90° Elbows 1) Except as permitted in Sentence (2), 90° elbows of NPS 4 or less whose centre-line radius is less than the NPS of the...