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The minimum required pipe size for water closets or pedestal urinal branches and stacks shall be 4 inches (100 mm).
Exception: A building three stories or less in height may utilize a 3-inch (75 mm) soil stack and 3-inch (75 mm) horizontal soil branches when not exceeding 48 fixture units, with not more than six water closets per soil stack and not more than three water closets per horizontal soil branch.
The minimum required pipe size for underground branches from downspouts, floor drains, laundry trays and sink stacks shall be 2 inches (51 mm).
(Amend Coun. J. 10-14-21, p. 37722, Art. VII, § 11; Amend Coun. J. 12-14-22, p. 58278, Art. VI, § 17)
Horizontal stack offsets shall be sized as required for building drains in accordance with Table 18-29-710A, except as required by Section 18-29-711.4.
Vertical stack offsets shall be sized as required for straight stacks in accordance with Table 18-29-710B, except when required to be sized as a building drain in accordance with Section 18-29-711.1.
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.
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.
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)
If a horizontal branch connects to the stack within 2 feet (610 mm) above or below a vertical stack offset, and the offset is located more than four branch intervals below the top of the stack, the offset shall be vented in accordance with Section 18-29-915.
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