Underground drainage piping.
Municipal Code of Chicago § 18-29-710.3
in effect18-29-710.3 Underground drainage piping.
Any portion of the drainage system installed underground or below a basement or cellar shall not be less than 2 inches (51 mm) in diameter.
Table 18-29-710A
Building Drains and Sewers
Diameter of Pipe (inches) | Maximum Number of Drainage Fixture Units Connected to any Portion of the Building Drain or the Building Sewer, Including Branches of the Building Drain a
Slope per Foot
1/16 inch | 1/8 inch | 1/4 inch | 1/2 inch
Diameter of Pipe (inches) | Maximum Number of Drainage Fixture Units Connected to any Portion of the Building Drain or the Building Sewer, Including Branches of the Building Drain a
Slope per Foot
1/16 inch | 1/8 inch | 1/4 inch | 1/2 inch
1 1/4 | – | – | 1 | 1
1 1/2 | – | – | 3 | 3
2 | – | – | 21 | 26
2 1/2 | – | – | 24 | 31
3 | – | 36 | 42 | 50
4 | – | 180 | 216 | 250
5 | – | 390 | 480 | 575
6 | – | 700 | 840 | 1,000
8 | 1,400 | 1,600 | 1,920 | 2,300
10 | 2,500 | 2,900 | 3,500 | 4,200
12 | 3,900 | 4,600 | 5,600 | 6,700
15 | 7,000 | 8,300 | 10,000 | 12,000
For SI: 1 inch = 25.4 mm, 1 inch per foot = 0.0833 mm/m.
a. The minimum size of any building drain serving a water closet shall be 3 inches.
Table 18-29-710B
Horizontal Fixture Branches and Stacks a
Diameter of Pipe (inches) | Any Horizontal Fixture Branch | Maximum Number of Fixture Units that may be Connected to:
One Stack of 3 Stories in Height or 3 Intervals | More than 3 Stories in Height
Total for Stack | Total at One Story or Branch Interval
Diameter of Pipe (inches) | Any Horizontal Fixture Branch | Maximum Number of Fixture Units that may be Connected to:
One Stack of 3 Stories in Height or 3 Intervals | More than 3 Stories in Height
Total for Stack | Total at One Story or Branch Interval
1 1/2 | 3 | 4 | 8 | 2
2 | 6 | 10 | 24 | 6
2 1/2 | 12 | 20 | 42 | 9
3 | 20 | 48 | 72 | 20
4 | 160 | 240 | 500 | 90
5 | 360 | 540 | 1,100 | 200
6 | 620 | 960 | 1,900 | 350
8 | 1,400 | 2,200 | 3,600 | 600
10 | 2,500 | 3,800 | 5,600 | 1,000
12 | 3,900 | 6,000 | 8,400 | 1,500
15 | 7,000 | Footnote c | Footnote c | Footnote c
For SI: 1 inch = 25.4 mm.
a. Does not include branches of the building drain. Refer to Table 18-29-710A.
b. Stacks shall be sized based on the total accumulated connected load at each story or branch interval. As the total accumulated connected load decreases, stacks are permitted to be reduced in size. Stack diameter shall not be reduced to less than one-half of the diameter of the largest stack size required.
c. Sizing load based on design criteria.
(Amend Coun. J. 10-14-21, p. 37722, Art. VII, § 11)
Source: City of Chicago, Municipal Code of Chicago (American Legal Publishing, codelibrary.amlegal.com)URL: https://codelibrary.amlegal.com/codes/chicago/latest/chicago_il/0-0-0-2692189Fetched: 10/24/2026