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Earlier editions: 20222019

Chapter 11 — STORM DRAINAGE

1107.2 Methods of Testing Storm Drainage Systems.

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.

Except for outside leaders and perforated or open-jointed drain tile, the piping of storm drain systems shall be tested upon completion of the rough piping installation by water or air, except that plastic pipe shall not be tested with air, and proved tight. The Authority Having Jurisdiction shall be permitted to require the removal of cleanout plugs to ascertain whether the pressure has reached parts of the system. One of the following test methods shall be used in accordance with Section 1107.2.1 through Section 1107.2.3. 1107.2.1 Water Test. After piping has been installed, the water test shall be applied to the drainage system, either to the entire system or sections. Where the test is applied to the entire system, all openings in the piping shall be tightly closed except for the highest opening, and the system shall be filled with water to the point of overflow. Where the system is tested in sections, each opening shall be tightly plugged except for the highest opening of the section under test, and each section shall be filled with water, but no section shall be tested with less than a 10 foot (3048 mm) head of water. In testing successive sections, not less than the upper 10 feet (3048 mm) of the next preceding section shall be tested so that no joint of pipe in the building except the uppermost 10 feet (3048 mm) of a roof drainage system, which shall be filled with water to the flood level of the uppermost roof drain, shall have been submitted to a test of less than 10 foot (3048 mm) head of water. The water shall be kept in the system or the portion of the test for not less than 15 minutes before inspection starts; the system shall then be tight. 1107.2.2 Air Test. The air test shall be made by attaching an air compressor testing apparatus to a suitable opening after closing other inlets and outlets to the system, forcing air into the system until there is a uniform gauge pressure of 5 pounds-force per square inch (psi) (34 kPa) or sufficient pressure to balance a column of mercury 10 inches (34 kPa) in height. This pressure shall be held without the introduction of additional air for not

less than 15 minutes.

1107.2.3 Exceptions. Where circumstances exist that make air and water tests described in Section 1107.2.1 and Section 1107.2.2 impractical, see Section 105.3.

STORM DRAINAGE

TABLE 1103.2 SIZING OF HORIZONTAL RAINWATER PIPING1, 2
SIZE OF PIPE FLOW
(1⁄8 inch per foot
slope)		 MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS AT VARIOUS RAINFALL RATES
(square feet)		 MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS AT VARIOUS RAINFALL RATES
(square feet)		 MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS AT VARIOUS RAINFALL RATES
(square feet)		 MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS AT VARIOUS RAINFALL RATES
(square feet)		 MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS AT VARIOUS RAINFALL RATES
(square feet)		 MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS AT VARIOUS RAINFALL RATES
(square feet)
inches gpm 1 (in/h) 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 34 3288 1644 1096 822 657 548
4 78 7520 3760 2506 1880 1504 1253
5 139 13 360 6680 4453 3340 2672 2227
6 222 21 400 10 700 7133 5350 4280 3566
8 478 46 000 23 000 15 330 11 500 9200 7670
10 860 82 800 41 400 27 600 20 700 16 580 13 800
12 1384 133 200 66 600 44 400 33 300 26 650 22 200
15 2473 238 000 119 000 79 333 59 500 47 600 39 650
SIZE OF PIPE FLOW
(1⁄4 inch per foot
slope)		 MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS AT VARIOUS RAINFALL RATES
(square feet)
inches gpm 1 (in/h) 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 48 4640 2320 1546 1160 928 773
4 110 10 600 5300 3533 2650 2120 1766
5 196 18 880 9440 6293 4720 3776 3146
6 314 30 200 15 100 10 066 7550 6040 5033
8 677 65 200 32 600 21 733 16 300 13 040 10 866
10 1214 116 800 58 400 38 950 29 200 23 350 19 450
12 1953 188 000 94 000 62 600 47 000 37 600 31 350
15 3491 336 000 168 000 112 000 84 000 67 250 56 000
SIZE OF PIPE FLOW
(1⁄2 inch per foot
slope)		 MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS AT VARIOUS RAINFALL RATES
(square feet)
inches gpm 1 (in/h) 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 68 6576 3288 2192 1644 1310 1096
4 156 15 040 7520 5010 3760 3010 2500
5 278 26 720 13 360 8900 6680 5320 4450
6 445 42 800 21 400 14 267 10 700 8580 7140
8 956 92 000 46 000 30 650 23 000 18 400 15 320
10 1721 165 600 82 800 55 200 41 400 33 150 27 600
12 2768 266 400 133 200 88 800 66 600 53 200 44 400
15 4946 476 000 238 000 158 700 119 000 95 200 79 300

For SI units: 1 inch = 25 mm, 1 gallon per minute = 0.06 L/s, [1] ⁄ 8 inch per foot = 10.4 mm/m, 1 inch per hour = 25.4 mm/h, 1 square foot = 0.0929 m [2]

Notes: 1 The sizing data for horizontal piping are based on the pipes flowing full. 2 For rainfall rates other than those listed, determine the allowable roof area by dividing the area given in the 1 inch per hour (25.4 mm/h) column by the desired rainfall rate.

210 2025 CALIFORNIA PLUMBING CODE

STORM DRAINAGE

TABLE 1103.3 SIZE OF GUTTERS
DIAMETER OF GUTTER
(1⁄16inch per foot slope)		 MAXIMUM RAINFALL RATES BASED ON ROOF AREA
(square feet)		 MAXIMUM RAINFALL RATES BASED ON ROOF AREA
(square feet)		 MAXIMUM RAINFALL RATES BASED ON ROOF AREA
(square feet)		 MAXIMUM RAINFALL RATES BASED ON ROOF AREA
(square feet)		 MAXIMUM RAINFALL RATES BASED ON ROOF AREA
(square feet)
inches 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 340 226 170 136 113
4 720 480 360 288 240
5 1250 834 625 500 416
6 1920 1280 960 768 640
7 2760 1840 1380 1100 918
8 3980 2655 1990 1590 1325
10 7200 4800 3600 2880 2400
DIAMETER OF GUTTER
(1⁄8 inch per foot slope)		 MAXIMUM RAINFALL RATES BASED ON ROOF AREA
(square feet)
inches 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 480 320 240 192 160
4 1020 681 510 408 340
5 1760 1172 880 704 587
6 2720 1815 1360 1085 905
7 3900 2600 1950 1560 1300
8 5600 3740 2800 2240 1870
10 10 200 6800 5100 4080 3400
DIAMETER OF GUTTER
(1⁄4 inch per foot slope)		 MAXIMUM RAINFALL RATES BASED ON ROOF AREA
(square feet)
inches 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 680 454 340 272 226
4 1440 960 720 576 480
5 2500 1668 1250 1000 834
6 3840 2560 1920 1536 1280
7 5520 3680 2760 2205 1840
8 7960 5310 3980 3180 2655
10 14 400 9600 7200 5750 4800
DIAMETER OF GUTTER
(1⁄2 inch per foot slope)		 MAXIMUM RAINFALL RATES BASED ON ROOF AREA
(square feet)
inches 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 960 640 480 384 320
4 2040 1360 1020 816 680
5 3540 2360 1770 1415 1180
6 5540 3695 2770 2220 1850
7 7800 5200 3900 3120 2600
8 11 200 7460 5600 4480 3730
10 20 000 13 330 10 000 8000 6660

For SI units: 1 inch = 25 mm, [1] ⁄ 16 inch per foot = 5.2 mm/m, 1 inch per hour = 25.4 mm/h, 1 square foot = 0.0929 m [2]

212 2025 CALIFORNIA PLUMBING CODE

CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE

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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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