1105.0 Controlled-Flow Roof Drainage.1105.1 Application.

Instead of sizing the storm drainage system in accordance with Section 1103.0, the roof drainage shall be permitted to be sized by controlled flow and storage of the storm water on the roof, provided the following conditions are met: (1) The water from a 25-year frequency storm shall not be

stored on the roof exceeding 24 hours.

(1) The water from a 25-year frequency storm shall not be

stored on the roof exceeding 24 hours. (2) During the storm, the water depth on the roof shall not

exceed the depths specified in Table 1105.1(1).

(2) During the storm, the water depth on the roof shall not

exceed the depths specified in Table 1105.1(1). (3) Not less than two drains shall be installed in roof areas of

10 000 square feet (929 m ² ) or less, and not less than one

• Vertical measurement from the roof surface at the drain to the highest point of the roof surface served by the drain, ignoring a local depression immediately adjacent to the drain.

(3) Not less than two drains shall be installed in roof areas of

10 000 square feet (929 m ² ) or less, and not less than one additional drain shall be installed for each 10 000 square feet (929 m ² ) of roof area exceeding 10 000 square feet (929 m ² ). (4) Each roof drain shall have a precalibrated, fixed (non adjustable), and proportional weir (notched) in a standing

TABLE 1105.1(2)

(4) Each roof drain shall have a precalibrated, fixed (non adjustable), and proportional weir (notched) in a standing water collar inside the strainer. No mechanical devices or valves shall be permitted. (5) Pipe sizing shall be based on the pre-calibrated rate of

flow (gpm) (L/s) of the pre-calibrated weir for the max

Pipe sizing shall be based on the pre-calibrated rate of

flow (gpm) (L/s) of the pre-calibrated weir for the maximum allowable water depth, and Table 1103.1 and Table 1103.2.

• Vertical measurement from the roof surface at the drain to the highest point of the roof surface served by the drain, ignoring a local depression immediately adjacent to the drain.

214 2019 CALIFORNIA PLUMBING CODE

STORM DRAINAGE