1. A. Vertical Leaders. Vertical leaders shall be sized for the maximum projected roof area, according to Table 1111.A of this code below. If a vertical offset is 45 degrees or less, the leader can be sized as a vertical pipe. If the offset is greater than 45 degrees, the pipe must be sized as a horizontal pipe.

   Table 1111.A Size of Vertical Leaders
   Size of Leader or Conductor1 (in)	Maximum Projected Roof Area (sq ft)
   2	720
   2 1/2	1300
   3	2200
   4	4600
   5	8650
   6	13,500
   8	29,000

   1. The equivalent diameter of square or rectangular leader may be taken as the diameter of that circle which may be inscribed within the cross-sectional area of the leader. See also §1111.B.2 of this code.

2. B. Building Storm Drains. Building storm drains shall comply with the following.

   1. 1. The size of the building storm drain or any of its horizontal branches having a slope of 1/2-inch or less per foot (41.6 mm/m) shall be based upon the maximum projected roof area to be handled according to Table 1111.B of this code below.

      Table 1111.B Size of Horizontal Storm Drains
      Diameter of Drain (in)	Maximum Projected Roof Area for Drains of Various Slopes (sq ft)
      	1/8 in Slope	1/4 in Slope	1/2 in Slope
      3	822	1,160	1,644
      4	1,880	2,650	3,760
      5	3,340	4,720	6,680
      6	5,350	7,550	10,700
      8	11,500	16,300	23,000
      10	20,700	29,200	41,400
      12	33,300	47,000	66,600
      15	59,500	84,000	119,000

   2. 2. Tables 1111.A and 1111.B of this code above are based upon a rate of rainfall of 4 inches (102 mm) per hour. If in any state, city or other political subdivision, the maximum rate of rainfall is more or less than 4 inches (102 mm) per hour, then the figures for roof area shall be adjusted proportionately by dividing the figure by four and multiplying by the maximum rate of rainfall in inches (mm) per hour. See §1111.E of this code.
3. C. Blockage Avoidance. To avoid stoppages, building drainage piping cannot be reduced in size in the direction of flow throughout its length. i.e., an 8-inch (203-mm) horizontal building storm drain must tie to an 8-inch (203-mm) vertical leader, even if Table 1111.A of this code allows for a smaller size for the vertical leader.
4. D. Vertical Walls. In sizing roof drains and storm drainage piping, one-half (1/2) of the area of any vertical wall which diverts rain water to the roof shall be added to the projected roof area for inclusion in calculating the required size of vertical leaders and horizontal storm drainage piping.

5. E. Maximum Rates of Rainfall. Primary roof drain systems shall be designed using Tables 1111.A and 1111.B of this code and adjusted in accordance with §1111.B.2 of this code for the local rainfall for a 60 minute duration and a 100-year return period in Figure 1111.E of this Part. The plumbing official may approve local weather data on the maximum rate of rainfall when available.

   Figure 1111.ERainfall Rate for Primary Roof Drains (in./hr.)

6. F. Parapet Wall Scupper Location. The location of parapet wall roof drainage scuppers and overflow scuppers shall be such that discharge can cause no personal injury or property damage. When neither conductor heads nor gutters are used to catch the water, scupper spouts shall extend past the exterior surface of the building to avoid wetting the building surface.

NOTE:

Authority Note

AUTHORITY NOTE: Promulgated in accordance with R.S. 40:4(A)(7) and R.S. 40:5(2)(3)(7)(9)(16)(17)(20).

Historical Note

HISTORICAL NOTE: Promulgated by the Department of Health and Hospitals, Office of Public Health, LR 38:2879 (November 2012).