Does anyone have a table of the maximum number of connections that drain/vent pipes can have for a given size?


It's not based on number of connections, but instead a computed value known as "drainage fixture units".

2012 International Residential Code


P3004.1 DWV system load. The load on DWV-system piping shall be computed in terms of drainage fixture unit (d.f.u.) values in accordance with Table P3004.1.

Table P3004.1


P3005.4.1 Branch and stack sizing. Branches and stacks shall be sized in accordance with Table P3005.4.1. Below grade drain pipes shall be not less than 11/2 inches (38 mm) in diameter. Drain stacks shall be not smaller than the largest horizontal branch connected.

1. A 4-inch by 3-inch (102 mm by 76 mm) closet bend or flange.
2. A 4-inch (102 mm) closet bend connected to a 3-inch (76 mm) stack tee shall not be prohibited.

Table P3005.4.1

P3005.4.2 Building drain and sewer size and slope. Pipe sizes and slope shall be determined from Table P3005.4.2 on the basis of drainage load in fixture units (d.f.u.) computed from Table P3004.1.

Table P3005.4.2

It seems that you are doing quite a bit of plumbing, and that you may not have all the knowledge required to do the work yourself. It might be a good idea to contact a local licensed Plumber, as they will be familiar with your local codes.

  • That's why I'm here, to gain knowledge :) Right now I'm in the exploratory phase. We're trying to design our basement renovation and trying to figure out what is possible. We'd really like to place the wet bar where we have it in the diagram, but seeing as it's in the middle of the room I wasn't sure what complications there might be. I find all of the answers very informative and fascinating! – 2 Left Thumbs Aug 9 '13 at 15:28
  • @2LeftThumbs That's why most of us are here, unfortunately, some things take years to learn and a lifetime to master. For small projects this site can be very helpful, but when you get in to larger projects, it's often good to seek professional advice from somebody familiar with local codes and practices. I can site code to you all day long, but in the end I am not a professional plumber. – Tester101 Aug 9 '13 at 16:56

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