Exception: The repair or replacement of an existing combined building sewer as of the initial adoption date of this code.
P-1109.3 Size of existing combined building drains and building sewers when adding additional load. The size of a combination sanitary and storm drain or sewer shall be computed in accordance with the method in Table 1109.4. The fixture units shall be converted into an equivalent projected roof or paved area. Allowance in square feet of pitched roofs or paved areas for fixture units shall be as follows: 7 square feet for each of the first 1,500 Fixture Units; 5 square feet for each of the next 1,500 Fixture Units, 4 square feet for each of the next 2,000 Fixture Units, and 3 square feet for each Fixture Unit thereafter. These values are based on a rainfall rate of 6 inches (127 mm) per hour. 330.1
Note: Bring in Table 1106.3 from the 2012 IPC for 6" rainfall rate only
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TABLE P-1109.4
MAXIMUM HORIZONTAL PROJECTED ROOF AREA IN SQUARE FEET FOR BUILDING STORM DRAINS AT VARIOUS SLOPES 330.2
MAXIMUM HORIZONTAL PROJECTED ROOF AREA IN SQUARE FEET FOR BUILDING STORM DRAINS AT VARIOUS SLOPES 330.2
Diameter (Inches) | Fall Per Foot | Vertical Leaders | ||
1/8" | 1/4" | 1/2" | ||
Diameter (Inches) | Fall Per Foot | Vertical Leaders | ||
1/8" | 1/4" | 1/2" | ||
3 | 930 | 1,300 | 1,750 | |
4 | 1,585 | 2,100 | 3,300 | 3,650 |
5 | 2,875 | 3,800 | 5,300 | 6,000 |
6 | 4,300 | 6,000 | 9,000 | 10,800 |
8 | 9,200 | 13,000 | 18,000 | 23,000 |
10 | 16,500 | 25,000 | 35,000 | 40,000 |
12 | 26,600 | 40,000 | 60,000 | 65,000 |
15 | 47,500 | 75,000 | 100,000 | 115,000 |
16 | 57,250 | 92,500 | 131,000 | |
18 | 67,000 | 110,000 | 162,000 | |
20 | 85,500 | 135,000 | 196,000 | |
24 | 155,000 | 225,000 | ||
30 | 295,000 | 416,000 | ||
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Notes
| 330.1 | Amended,
Bill No. 230653 (approved December 20, 2023), effective April 1, 2024. |
| 330.2 | Amended,
Bill No. 230653 (approved December 20, 2023), effective April 1, 2024. |