In working to cross my i's and dot my t's I found this section in IRC2015 and no matter how many times I read it, I have no idea what it's talking about. Can someone give an explanation as to what it is talking about, maybe a sketch? P3005.5 Connections to Offsets and Bases of Stacks. Horizontal branches shall connect to the bases of stacks at a point located not less than 10 times the diameter of the drainage stack downstream from the stack. Horizontal branches shall connect to horizontal stack offsets at a point located not less than 10 times the diameter of the drainage stack downstream from the upper stack. I'm not a fan of double negatives in code statements, but can't get my head around what is going on. I'm thinking of branches connecting to stacks (sanitary tee, or a wye, etc) and being low on the stack. What am I missing from where branches connect anyplace in the DWV system. Is there something I'm missing in "base of stack". Does it have a more specific meaning. For me "base of stack" is anyplace near the floor, where it's elbow takes the stack horizontal. Is there something more specific here. I need to connect horizontal branches to my vertical stack in my basement just above the base of the stack, which was fine till I read this and started to wonder if I was suddenly missing something.