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The Building code for Wisconsin states this:

  1. The minimum radius for the first 90° fitting downstream from a trap serving a lavatory or sink shall be 1-3/4" for drain piping 1-1/2" in diameter. The fitting shall be a tee or quarter bend.
  2. The minimum radius for the first 90° bend or elbow downstream from a water closet shall be 2-1/2" for drain piping 3" in diameter.
  3. The minimum radius for the first 90° bend or elbow downstream from a water closet shall be 3" for drain piping 4" in diameter.

Could I get a translation, please? This sounds like it's either poorly worded or unrealistic. The "minimum radius"? So downstream of a sink, if I want a 90 degree turn, I need to increase to a diameter of 3 1/2 inches? That sounds absurd. There appears to be no such thing as a 3 1/2 inch PVC pipe at the average hardware store.

I was under the impression that I could do long runs with multiple 90 degree turns, maintaining 1 1/2 inch diameter as long as I use long-turn fittings.

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Bend radius, not cross-sectional radius. Pipes are never sized by radius, but by inner diameter.

They want you to use elbows other than those with the sharp 90-degree corner at the inside, such as this one:

enter image description here

Instead, use standard elbows (or longer):

enter image description here

  • So basically, "use long-turn fittings". – Sildoreth Jan 17 at 21:47
  • No. You can use standard elbows. – isherwood Jan 17 at 21:47

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