Size.
Municipal Code of Chicago § 18-29-912.3
in effect18-29-912.3 Size.
The minimum size of a combination drain and vent pipe shall be in accordance with Table 18-29-912.3.
Table 18-29-912.3
Size of Combination Drain and Vent Pipe
(for Floor Drains Only)
Diameter Pipe (inches) | Maximum Number of Drainage Fixture Units
Connecting to a horizontal branch or stack | Connecting to a building drain or building subdrain
Diameter Pipe (inches) | Maximum Number of Drainage Fixture Units
Connecting to a horizontal branch or stack | Connecting to a building drain or building subdrain
2 | 3 | 4
2 1/2 | 6 | 26
3 | 12 | 31
4 | 20 | 50
5 | 160 | 250
6 | 360 | 575
For SI: 1 inch = 25.4 mm.
Source: City of Chicago, Municipal Code of Chicago (American Legal Publishing, codelibrary.amlegal.com)URL: https://codelibrary.amlegal.com/codes/chicago/latest/chicago_il/0-0-0-2692522Fetched: 10/24/2026