Louisiana Administrative Code
Title 51 - PUBLIC HEALTH-SANITARY CODE
Part XIV - Plumbing
Chapter 11 - Storm Drainage
Section XIV-1111 - Size of Leaders and Storm Drains

Universal Citation: LA Admin Code XIV-1111

Current through Register Vol. 50, No. 9, September 20, 2024

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

NOTE:

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.

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

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. 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.

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.

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.

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.

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Figure 1111.E - Rainfall Rate for Primary Roof Drains (in./hr.)

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.

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

Disclaimer: These regulations may not be the most recent version. Louisiana may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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