Size of Conductors, Leaders and Storm Drains
NYC Plumbing Code § PC 1106
in effectSection PC 1106: Size of Conductors, Leaders and Storm Drains
1106.1 General.
The size of the vertical conductors and leaders, gutters, building storm drains, building storm sewers and any horizontal branches of such drains or sewers shall be based on the 100-year hourly rainfall rate of 3 inches (76 mm) per hour. Sizing for secondary and combined primary and secondary conductors, leaders and drains shall be in accordance with Section 1108.
(Am. L.L. 2023/077, 6/11/2023, eff. 6/11/2023)
Editor's note: For related unconsolidated provisions, see Appendix A at L.L. 2023/077.
1106.2 Size of storm drain piping.
Vertical and horizontal storm drain piping shall be sized based on the flow rate through the roof drain. The flow rate in storm drain piping shall not exceed that specified in Table 1106.2.
Table 1106.2
Storm Drain Pipe Sizing
Pipe Size (inches) Capacity (gpm)
Vertical Drain Slope of Horizontal Drain
1/16 inch per foot 1/8 inch per foot 1/4 inch per foot 1/2 inch per foot
2 34 15 22 31 44
3 87 39 55 79 111
4 180 81 115 163 231
5 311 117 165 234 331
6 538 243 344 487 689
8 1,117 505 714 1,010 1,429
10 2,050 927 1,311 1,855 2,623
12 3,272 1,480 2,093 2,960 4,187
14 4,204 1,312 1,856 2,621 3,713
15 5,543 2,508 3,546 5,016 7,093
16 5,543 2,508 3,546 5,016 7,093
18 8.218 3,100 4,386 6,192 8,773
1106.2.1 Values for continuous flow.
Where there is a continuous or semicontinuous discharge into the building storm drain or building storm sewer, such as from a pump, ejector, air conditioning plant or similar device, each gallon per minute of such discharge shall be computed as being equivalent to 32 square feet (2.97 m2) of roof area, based on a rainfall rate of 3 inches (75 mm) per hour.
1106.3 Vertical leader sizing.
Vertical leaders shall be sized based on the flow rate from horizontal gutters or the maximum flow rate through roof drains. The flow rate through vertical leaders shall not exceed that specified in Table 1106.3.
Table 1106.3
Vertical Leader Sizing
Size of Leader (inches) Capacity (gpm)
2 30
2 × 2 30
1 1/2 × 2 1/2 30
2 1/2 54
2 1/2 × 2 1/2 54
3 92
2 × 4 92
2 1/2 × 3 92
4 192
3 × 4 1/4 192
3 1/2 × 4 192
5 360
4 × 5 360
4 1/2 × 4 1/2 360
6 563
5 × 6 563
5 1/2 × 5 1/2 563
8 1208
6 × 8 1208
For SI: 1 inch = 25.4 mm, 1 gallon per minute = 3.785 L/m.
1106.4 Vertical walls.
In sizing roof drains and storm drainage piping, one-fourth of the area of any vertical wall that diverts rainwater to the roof or the setback roof of a building shall be added to the projected roof area for inclusion in calculating the required size of vertical conductors, leaders and horizontal storm drainage piping.
Exceptions:
1. Where vertical conductors or leaders and downstream piping has been sized for secondary roof drainage in accordance with Section 1108, the contribution from vertical walls need not be added to the projected roof area.
2. Section 1106.4 shall not be applicable to vertical walls fronting a public right-of-way.
1106.5 Parapet wall scupper location.
Parapet wall roof drainage scupper and overflow scupper location shall comply with the requirements of Section 1503.4 of the New York City Building Code.
1106.6 Size of roof gutters.
Horizontal gutters shall be sized based on the flow rate from the roof surface. The flow rate in horizontal gutters shall not exceed that specified in Table 1106.6.
Table 1106.6
Horizontal Gutter Sizing
Gutter Dimensions a (inches) Slope (inch per foot) Capacity (gpm)
1 1/2 × 2 1/2 1/4 26
1 1/2 × 2 1/2 1/2 40
4 1/8 39
2 1/4 × 3 1/4 55
2 1/4 × 3 1/2 87
5 1/8 74
4 × 2 1/2 1/4 106
3 × 3 1/2 1/2 156
6 1/8 110
3 × 5 1/4 157
3 × 5 1/2 225
8 1/16 172
8 1/8 247
4 1/2 × 6 1/4 348
4 1/2 × 6 1/2 494
10 1/16 331
10 1/8 472
5 × 8 1/4 651
4 × 10 1/2 1055
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 3.785 L/m, 1 inch per foot = 83.3 mm/m.
a. Dimensions are width by depth for rectangular shapes. Single dimensions are diameters of a semicircle.
Source: City of New York, Charter, Administrative Code and Rules (American Legal Publishing XML export, codelibrary.amlegal.com)URL: https://codelibrary.amlegal.com/codes/newyorkcity/latest/NYCadmin/0-0-0-163440Fetched: 10/24/2026