18-29-1110.1.1 Design.

   The flow rate (gpm) shall be determined by the use of Chart 18-29-1110.1.1 A for flat roofs and Chart 18-29-1110.1.1 B for slope roofs. The size of the vertical pipe and horizontal pipe shall be determined by the use of Tables 18-29-1110.1.1 C for vertical pipe and Table 18-29-1110.1.1 D for horizontal pipe and in no case shall be less than 3 inches (75 mm). The capacity rating (gpm) of any controlled flow downspout, branch or storm drain shall be converted to an equivalent square foot area by multiplying the gallons per minute (gpm) by 24 (24 square feet of roof area equals 1 gpm) before connecting to any combined house drain or house sewer, and add this value to the total drained area of Section 18-29-1106 of this chapter. Downspouts that are offset at 90 degrees shall be full size to the storm drain or sewer or combined drain or sewer.

Chart 18-29-1110.1.1 A and
Chart 18-29-1110.1.1 B

Table 18-29-1110.1.1

Diameter of Downspout	Max. Horizontal Projected Roof Area Square Feet
2"	720
2 1/2"	1,300
3"	2,150
4"	4,600
5"	8,300
6"	13,000
8"	29,000
10"	52,000
12"	83,000
13"	155,000

 

Table 18-29-1110.1.1C
Vertical

Diameter of Downspout	Max. Vertical Projected Roof Area Square Feet
3"	88
4"	190
5"	345
6"	560
8"	1,210
10"	2,185
12"	3,570
15"	6,450

 

Table 18-29-1110.1.1D
Horizontal

Maximum Controlled Flow in GPM
Pipe Diameter in Inches	Slope in Inches in gpm
	1/2	1/4	1/8	1/16
3"	72	51	N.P.	N.P.
4"	156	110	78	N.P.
5"	282	200	140	N.P.
6"	460	325	230	N.P.
8"	990	700	495	N.P.
10"	1,795	1,265	895	630
12"		2,065	1,460	1,030
15"			2,650	1,870

 

18-29-1110.2 Control devices.

   The control devices shall be installed so that the rate of discharge of water per minute shall not exceed the values for continuous flow as indicated in Section 18-29-1110.1.1. A scupper drain or drains shall be placed in the parapet wall at an invert elevation 1/2 inch (12 mm) above the maximum designed head. The scupper shall have a cross sectional area equal to that as required for conventional roof drainage. Control of runoff from roofs shall be by pre-calibrated tamper proof weirs; no valves or mechanical devices shall be permitted.

   Exception: Scuppers are not permitted in fire walls provided in accordance with Chapter 15-8 or 14B-7, as applicable.

(Amend Coun. J. 4-10-19, p. 100029, Art. XVI, § 13)

18-29-1110.3 Installation.

   Runoff control shall be by control devices. Control devices shall be protected by strainers.

18-29-1110.4 Minimum number of roof drains.

   Not less than two drains shall be installed in roof areas 10,000 square feet (930 m 2 ) or less and not less than four roof drains shall be installed in roofs over 10,000 square feet (930 m 2 ) in area.

18-29-1111 Sumps.