Minimum Size of First 90 Degree Fitting Downstream of a Sink

Question

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.

Answer 1

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:

Instead, use standard elbows (or longer):