IRC P3005.5 Connections to offsets and bases of stacks: Explain Please

Discussion in 'IPC Plumbing Code Questions' started by WoodenTent, Jan 21, 2017.

  1. WoodenTent

    WoodenTent New Member

    Dec 27, 2015
    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.
  2. utah student

    utah student New Member

    Apr 17, 2018
    I believe having a pipe to close to the base of the stake might cause what is called a "hydraulic jump". From my understanding if this happens it could mess with your trap seals because of pressure fluctuation. Keeping the branch connections 10 dia from there helps keep a more uniform flow. If I am wrong I would like to hear why so I can also learn from this.
  3. Sponsor

    Sponsor Paid Advertisement

  4. Sylvan

    Sylvan Still learning

    Sep 23, 2004
    plumbing - fire suppression - boiler inspector
    New York
  5. hj

    hj Master Plumber

    Aug 31, 2004
    Cave Creek, Arizona
    There are NO "double negatives". They are referring to the horizontal section AFTER it makes the turn at the base of the stack. You cannot connect between the turn and the required downstream distance.

Share This Page