Page 111 - 2018_IPC

STORM DRAINAGE

1106.2 Size of storm drain piping. Vertical and horizontal SECTION 1108
storm drain piping shall be sized based on the flow rate SECONDARY (EMERGENCY) ROOF DRAINS
through the roof drain. The flow rate in storm drain piping 1108.1 Secondary (emergency overflow) drains or scup-
shall not exceed that specified in Table 1106.2. pers. Where roof drains are required, secondary (emergency
1106.3 Vertical leader sizing. Vertical leaders shall be sized overflow) roof drains or scuppers shall be provided where the
based on the flow rate from horizontal gutters or the maxi- roof perimeter construction extends above the roof in such a
mum flow rate through roof drains. The flow rate through manner that water will be entrapped if the primary drains
vertical leaders shall not exceed that specified in Table allow buildup for any reason. Where primary and secondary
1106.3. roof drains are manufactured as a single assembly, the inlet
1106.4 Vertical walls. In sizing roof drains and storm drain- and outlet for each drain shall be independent.
age piping, one-half of the area of any vertical wall that TABLE 1106.3
diverts rainwater to the roof shall be added to the projected VERTICAL LEADER SIZING
roof area for inclusion in calculating the required size of ver-
SIZE OF LEADER CAPACITY
tical conductors, leaders and horizontal storm drainage pip- (inches) (gpm)
ing. 2 30
1106.5 Parapet wall scuppers. Where scuppers are used for 2 × 2 30
primary roof drainage or for secondary (emergency overflow) 1 1
roof drainage or both, the quantity, size, location and inlet 1 / × 2 / 2 30
2
1
elevation of the scuppers shall be chosen to prevent the depth 2 / 2 54
of ponding water on the roof from exceeding the maximum 2 / × 2 / 54
1
1
water depth that the roof was designed for as determined by 2 2
Section 1611.1 of the International Building Code. Scupper 3 92
openings shall be not less than 4 inches (102 mm) in height 2 × 4 92
and have a width that is equal to or greater than the circum- 2 / × 3 92
1
2
ference of a roof drain sized for the same roof area. The flow 4 192
through the primary system shall not be considered when
1
locating and sizing secondary scuppers. 3 × 4 / 4 192
1
1106.6 Size of roof gutters. Horizontal gutters shall be sized 3 / × 4 192
2
based on the flow rate from the roof surface. The flow rate in 5 360
horizontal gutters shall not exceed that specified in Table 4 × 5 360
1106.6.
1
1
4 / × 4 / 360
2 2
6 563
SECTION 1107
SIPHONIC ROOF DRAINAGE SYSTEMS 5 × 6 563
1
1
5 / × 5 / 563
1107.1 General. Siphonic roof drains and drainage systems 2 2
shall be designed in accordance with ASME A112.6.9 and 8 1208
ASPE 45. 6 × 8 1208
For SI: 1 inch = 25.4 mm, 1 gallon per minute = 3.785 L/m.
TABLE 1106.2
STORM DRAIN PIPE SIZING
CAPACITY (gpm)
PIPE SIZE SLOPE OF HORIZONTAL DRAIN
(inches) VERTICAL DRAIN
1 1 1 1
/ 16 inch per foot / 8 inch per foot / 4 inch per foot / 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
15 5,543 2,508 3,546 5,016 7,093
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 3.785 L/m.

94 2018 INTERNATIONAL PLUMBING CODE ®
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