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Earlier editions: 20222019

Chapter 11 — STORM DRAINAGE

1105.1 Application. Instead of sizing the storm drainage

California Plumbing Code (Title 24, Part 5) · 2025 edition · updated 2026-09-10 · California

Italicized text is a California amendment to the model code, as printed in the official publication.

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. (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 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 (nonadjustable), 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 maximum allowable water depth, and Table 1103.1 and Table 1103.2.

(6) The height of stones or other granular material above the waterproofed surface shall not be considered in water depth measurement, and the roof surface in the vicinity of the drain shall not be recessed to create a reservoir.

(7) Roof design, where controlled-flow roof drainage is used, shall be such that the design roof live load is not less than 30 lb/ft [2] (146 kg/m [2] ) to provide a safety factor exceeding the 15 lb/ft [2] (73 kg/m [2] ) represented by the depth of water stored on the roof in accordance with Table 1105.1(1). (8) Scuppers shall be provided in parapet walls. The distance of scupper bottoms above the roof level at the drains shall not exceed the maximum distances specified in Table 1105.1(2).

(9) Scupper openings shall be not less than 4 inches (102 mm) high and have a width equal to the circumference of

208 2025 CALIFORNIA PLUMBING CODE

STORM DRAINAGE

the roof drain required for the area served, sized in accordance with Table 1103.1.

(10)Flashings shall extend above the top of the scuppers.

(11)At a wall or parapet, 45 degree (0.79 rad) cants shall be installed.

(12)Separate storm and sanitary drainage systems shall be provided within the building.

(13)Calculations for the roof drainage system shall be submitted along with the plans to the Authority Having Jurisdiction for approval.

TABLE 1105.1(1) CONTROLLED-FLOW MAXIMUM ROOF WATER DEPTH

ROOF RISE*
(inches)		 MAXIMUM WATER DEPTH AT
DRAIN
(inches)

Flat		 3

2		 4

4		 5

6		 6

For SI units: 1 inch = 25.4 mm

  • 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.

TABLE 1105.1(2) DISTANCE OF SCUPPER BOTTOMS ABOVE ROOF

ROOF RISE*
(inches)		 ABOVE ROOF LEVEL
AT DRAIN
(inches)

Flat		 3

2		 4

4		 5

6		 6

For SI units: 1 inch = 25.4 mm

  • 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.

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▸Contents — California Plumbing Code (Title 24, Part 5)
California Plumbing Code (Title 24, Part 5)
  1. Chapter 1 — GENERAL CODE PROVISIONS
  2. Chapter 2 — DEFINITIONS
  3. Chapter 3 — GENERAL REGULATIONS
  4. Chapter 4 — PLUMBING FIXTURES AND FIXTURE FITTINGS
  5. Chapter 5 — WATER HEATERS
  6. Chapter 6 — WATER SUPPLY AND DISTRIBUTION
  7. Chapter 7 — SANITARY DRAINAGE
  8. Chapter 8 — INDIRECT WASTES
  9. Chapter 9 — VENTS
  10. Chapter 10 — TRAPS AND INTERCEPTORS
  11. ▸Chapter 11 — STORM DRAINAGE
    Overview
    1. 1101.1 Applicability. This chapter shall govern the materials,…
    2. 1101.2 Where Required. Roofs, paved areas, yards, courts,
    3. 1101.3 Storm Water Drainage to Sanitary Sewer Pro-
    4. 1101.4 Material Uses. Pipe, tube, and fittings conveying
    5. 1101.5 Expansion Joints Required. Expansion joints or
    6. 1101.6 Subsoil Drains. Subsoil drains shall be provided
    7. 1101.7 Building Subdrains. Building subdrains located
    8. 1101.8 Areaway Drains. Open subsurface space adjacent
    9. 1101.9 Window Areaway Drains. Window areaways at a
    10. 1101.10 Filling Stations and Motor Vehicle Washing
    11. 1101.11 Paved Areas. Where the occupant creates surface
    12. 1101.12 Roof Drainage. Roof drainage shall comply with
    13. 1101.13 Cleanouts. Cleanouts for building storm drains
    14. 1101.14 Rainwater Sumps. Rainwater sumps serving
    15. 1101.15 Traps on Storm Drains and Leaders. Leaders
    16. 1101.16 Leaders, Conductors, and Connections.
    17. 1102.1 Applications. Roof drains shall be constructed of
    18. 1102.2 Dome Strainers Required. Roof drains shall have
    19. 1102.3 Roof Drain Flashings. The connection between
    20. 1103.1 Vertical Conductors and Leaders. Vertical conductors an…
    21. 1103.2 Size of Horizontal Storm Drains and Sewers.
    22. 1103.3 Size of Roof Gutters. The size of semi-circular
    23. 1103.4 Side Walls Draining onto a Roof. Where vertical walls p…
    24. 1104.1 General. Where there is a continuous or semi-continuous…
    25. 1105.1 Application. Instead of sizing the storm drainage
    26. 1105.2 Setback Roofs. Drains on setback roofs shall be
    27. 1106.1 General. The design and sizing of a storm drainage
    28. 1106.2 Siphonic Roof Drainage Systems. The design of
    29. 1106.3 Siphonic Roof Drains. Siphonic roof drains shall
    30. 1107.1 Testing Required. New building storm drainage
    31. 1107.2 Methods of Testing Storm Drainage Systems.
  12. Chapter 12 — FUEL GAS PIPING
  13. Chapter 13 — HEALTH CARE FACILITIES AND MEDICAL GAS AND MEDICA…
  14. Chapter 14 — FIRESTOP PROTECTION
  15. Chapter 15 — ALTERNATE WATER SOURCES FOR NONPOTABLE APPLICATIONS
  16. Chapter 16 — NONPOTABLE RAINWATER CATCHMENT SYSTEMS
  17. Chapter 17 — REFERENCED STANDARDS
  18. Appendix A — RECOMMENDED RULES FOR SIZING THE WATER SUPPLY SYS…
  19. Appendix B — EXPLANATORY NOTES ON COMBINATION WASTE AND VENT S…
  20. Appendix C — ALTERNATE PLUMBING SYSTEMS
  21. Appendix D — SIZING STORM WATER DRAINAGE SYSTEMS
  22. Appendix E — MANUFACTURED/MOBILE HOME PARKS AND RECREATIONAL V…
  23. Appendix F — FIREFIGHTER BREATHING AIR REPLENISHMENT SYSTEMS
  24. Appendix G — SIZING OF VENTING SYSTEMS
  25. Appendix H — PRIVATE SEWAGE DISPOSAL SYSTEMS
  26. Appendix I — INSTALLATION STANDARDS
  27. Appendix J — COMBINATION OF INDOOR AND OUTDOOR COMBUSTION AND …
  28. Appendix K — POTABLE RAINWATER CATCHMENT SYSTEMS
  29. Appendix L — SUSTAINABLE PRACTICES
  30. Appendix M — PEAK WATER DEMAND CALCULATOR
  31. Appendix N — IMPACT OF WATER TEMPERATURE ON THE POTENTIAL FOR …
  32. Appendix O — NON-SEWERED SANITATION SYSTEMS
  33. Appendix P — PROFESSIONAL QUALIFICATIONS
  34. Appendix Q — INDOOR HORTICULTURAL FACILITIES
  35. Appendix R — TINY HOUSES
  36. Appendix S — ONSITE STORMWATER TREATMENT SYSTEMS

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