SECTION P-1109 COMBINED SANITARY AND STORM PUBLIC SEWER

P-1109.1 General. Where the public sewer is a combined system for both sanitary and storm water, the storm sewer shall be connected independently to the lateralpublic sewer.

Exception: The repair or replacement of an existing combined building sewer as of the initial adoption date of this code.

P-1109.2 Size of the existing combined building drains and building sewers. The size of the existing combined building drains and building sewers when being replaced in kind shall not be less than 4" and not having a slope less than 1/8" per foot (1 percent).

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. Where the total fixture load on the combined drain is less than or equal to 256 fixture units, the equivalent drainage area in horizontal projection shall be taken as 4,000 square feet (372 m 2). Where the total fixture load exceeds 256 fixture units, each additional fixture unit shall be considered the equivalent of 15.6 square feet (1.5 m 2) of drainage area. These values are based on a rainfall rate of 6" (127 mm) per hour.

Note: Bring in Table 1106.3 from the 2012 IPC for 6" rainfall rate only

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TABLE P-1109.4
SIZE OF HORIZONTAL STORM DRAINAGE PIPING

 

SIZE OF HORIZONTAL PIPE

HORIZONTALLY PROJECTED ROOF AREA (square feet)

1/8 unit vertical in 12 units horizontal (1% slope)
3	548
4	1,253
5	2,227
6	3,566
8	7,600
10	13,800
12	22,200
15	39,650
1/4 unit vertical in 12 units horizontal (2% slope)
3	773
4	1,766
5	3,146
6	5,033
8	10,866
10	19,450
12	31,350
15	56,000
1/2 unit vertical in 12 units horizontal (4% slope)
3	1,096
4	2,500
5	4,450
6	7,140
8	15,320
10	27,600
12	44,400
15	79,250

 

For SI: 1 inch = 25.4 mm, 1 square foot = 0.0929 m2

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