CPC · California Plumbing Code

Sizing of leaders, storm drains, gutters and controlled-flow systems

This hub summarizes CPC Chapter 11 rules and tables for sizing leaders, gutters, roof and storm drains, controlled‑flow systems, and related testing and engineered‑system requirements.

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Last reviewed: July 6, 2026

Overview

This section of the California Plumbing Code (CPC) governs sizing and installation of roof drainage components — vertical leaders/conductors, roof drains, gutters, horizontal building storm drains, and controlled‑flow roof drainage — and includes tables and required procedures for testing and engineered systems. See §1103.0 for sizing of leaders, conductors and storm drains and the sizing tables for vertical and horizontal rainwater piping, and §1102.0 for roof‑drain requirements . Controlled‑flow roof drainage and its limiting depths and scupper distances are addressed in Chapter 11 at §1105.0 and its tables, with engineered or siphonic systems covered under §1106.0 and testing requirements at §1107.0 .

Proper application matters because roof and site drainage affect structural loading (ponding), interior water intrusion, public safety and storm‑sewer capacity. The CPC requires coordinating drain/gutter locations and sizes with roof geometry and structural design and normally sizes primary drainage for a 60‑minute, 100‑year storm (see §1101.12), with specific provisions for secondary (emergency) drainage and combined systems .

You’ll use the CPC tables (Table 1103.1 for vertical leaders/roof drains, Table 1103.2 for horizontal storm piping, Table 1103.3 for gutters) and the controlled‑flow tables (Table 1105.1(1) and (2)) to convert roof area and design rainfall to pipe and gutter sizes; engineered exceptions (siphonic or other designs) must be prepared by a registered design professional and approved per §1106.0 .

In this section

Code references

Grounded in the retrieved California Plumbing Code — click a citation to read the verbatim passage:

CPC § 1103.0 High relevance — show source text

1103.0 Size of Leaders, Conductors, and Storm Drains.

1103.1 Vertical Conductors and Leaders. Vertical conductors and leaders shall be sized by the maximum projected roof area and Table 1103.1.

1103.2 Size of Horizontal Storm Drains and Sewers. The size of building storm drains, or building storm sewers or their horizontal branches shall be based on the maximum projected roof or paved area to be handled and Table 1103.2.

1103.3 Size of Roof Gutters. The size of semi-circular gutters shall be based on the maximum projected roof area and Table 1103.3.

1103.4 Side Walls Draining onto a Roof. Where vertical walls project above a roof to permit storm water to drain into the roof area below, the adjacent roof area shall be permitted to be computed from Table 1103.1 as follows:

(1) For one wall – add 50 percent of the wall area to the roof area figures.

(2) For two adjacent walls of equal height – add 35 percent of the total wall areas.

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STORM DRAINAGE

Col1	Col2	TABLE 1103.1 SIZING ROOF DRAINS, LEADERS, AND VERTICAL RAINWATER PIPING2, 3	Col4	Col5	Col6	Col7	Col8	Col9	Col10	Col11	Col12	Col13	Col14
SIZE OF DRAIN, LEADER, OR PIPE	FLOW	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)	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

CPC § 1101.16 High relevance — show source text
1101.16 Leaders, Conductors, and

Connections . . . . . . . . . . . . . . . . .207

1102.0 Roof Drains . . . . . . . . . . . . . . . . . .207

1102.1 Applications . . . . . . . . . . . . . . . . .207

1102.2 Dome Strainers Required . . . . . . .207

1102.3 Roof Drain Flashings . . . . . . . . . .207

1103.0 Size of Leaders, Conductors,

and Storm Drains . . . . . . . . . . . . .207

1103.1 Vertical Conductors and

Leaders . . . . . . . . . . . . . . . . . . . . .207

1103.2 Size of Horizontal Storm

Drains and Sewers . . . . . . . . . . . .207

1103.3 Size of Roof Gutters . . . . . . . . . . .207

1103.4 Side Walls Draining onto a Roof . . . . . . . . . . . . . . . . . .207

Table 1103.1 Sizing Roof Drains, Leaders, and Vertical Rainwater Piping . . .208

1104.0 Values for Continuous Flow . . . . .208

1104.1 General . . . . . . . . . . . . . . . . . . . . .208

1105.0 Controlled-Flow Roof

Drainage . . . . . . . . . . . . . . . . . . . .208

1105.1 Application . . . . . . . . . . . . . . . . . .208

Table 1105.1(1) Controlled-Flow Maximum Roof Water Depth . . . . . . . . . . . . .209

Table 1105.1(2) Distance of Scupper Bottoms Above Roof . . . . . . . . . . . . . . . . . .209

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TABLE OF CONTENTS

1105.2 Setback Roofs . . . . . . . . . . . . . . .209

1106.0 Engineered Storm Drainage System . . . . . . . . . . . . . . . . . . . . .209

1106.1 General . . . . . . . . . . . . . . . . . . . . .209

1106.2 Siphonic Roof Drainage Systems . . . . . . . . . . . . . . . . . . . .209

1106.3 Siphonic Roof Drains . . . . . . . . . .209

1107.0 Testing . . . . . . . . . . . . . . . . . . . . .209

1107.1 Testing Required . . . . . . . . . . . . .209

1107.2 Methods of Testing Storm Drainage Systems . . . . . . . . . . . .209

Table 1103.2 Sizing of Horizontal Rainwater Piping . . . . . . . . . . . . .210

Table 1103.3 Size of Gutters . . . . . . . . . . . . . . .211

CPC § 106.3 High relevance — show source text

K 106.3 Roof Gutters. Gutters shall maintain a minimum slope and be sized in accordance with this code. K 106.4 Drains, Conductors, and Leaders. The design and size of rainwater drains, conductors, and leaders shall comply with this code. K 106.5 Size of Potable Water Piping. Potable rainwater system distribution piping shall be sized in accordance with this code for sizing potable water piping.

K 107.0 Cleaning. K 107.1 General. The interior surfaces of tanks and equipment shall be clean before they are put into service.

K 108.0 Supply System Inspection and Test. K 108.1 General. Rainwater catchment systems shall be inspected and tested in accordance with the applicable provisions of this code for testing of potable water and storm drainage systems. Storage tanks shall be filled with water to the overflow opening for 24 hours, and during the inspection, or by other means as approved by the Authority Having Jurisdiction. Seams and joints shall be exposed during the inspection and checked for water tightness.

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CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE

APPENDIX L - SUSTAINABLE PRACTICES

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

Adopting Agency	BSC	BSC- CG	SFM	HCD	Col6	Col7	DSA	Col9	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	Col17	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting Agency	BSC	BSC- CG	SFM	1	2	1-AC	AC	SS	SS/CC	1	1R	2	3	4	5	6	6	6	6	6	6	6	6	6
Adopt Entire Chapter
Adopt Entire Chapter as amended (amended sections listed below)
Adopt only those sections that are listed below
Chapter/Section

This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.

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CPC § 106.2.1 High relevance — show source text
K 106.2.1 Size. The roof washer shall be sized to direct rainwater containing debris that has accumulated on the collection surface away from the storage tank. ARCSA/ASPE/ANSI 63 contains additional guidance on acceptable methods of sizing roof washers.

K 106.2.2 Debris Screen. The inlet to the roof washer shall be provided with a debris screen or other approved means that protects the roof washer from the intrusion of debris and vermin. Where the debris screen is installed, the debris screen shall be corrosion resistant and shall have openings not larger than [1] ⁄ 2 of an inch (12.7 mm). K 106.2.3 Drain Discharge. Water drained from the roof washer, or pre-filter shall be diverted away from the storage tank and discharged to a disposal area that does not cause property damage or erosion. Roof washer drainage shall not drain over a public way. K 106.2.4 Automatic Drain. Roof washing systems shall be provided with an automatic means of self-draining between rain events.

K 106.3 Roof Gutters. Gutters shall maintain a minimum slope and be sized in accordance with this code. K 106.4 Drains, Conductors, and Leaders. The design and size of rainwater drains, conductors, and leaders shall comply with this code. K 106.5 Size of Potable Water Piping. Potable rainwater system distribution piping shall be sized in accordance with this code for sizing potable water piping.

K 107.0 Cleaning. K 107.1 General. The interior surfaces of tanks and equipment shall be clean before they are put into service.

K 108.0 Supply System Inspection and Test. K 108.1 General. Rainwater catchment systems shall be inspected and tested in accordance with the applicable provisions of this code for testing of potable water and storm drainage systems. Storage tanks shall be filled with water to the overflow opening for 24 hours, and during the inspection, or by other means as approved by the Authority Having Jurisdiction. Seams and joints shall be exposed during the inspection and checked for water tightness.

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CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE

APPENDIX L - SUSTAINABLE PRACTICES

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
CPC § 1101.1 High relevance — show source text
1101.1 Applicability . . . . . . . . . . . . . . . . . .205

1101.2 Where Required . . . . . . . . . . . . . .205

1101.3 Storm Water Drainage to Sanitary Sewer Prohibited . . . . . .205

1101.4 Material Uses . . . . . . . . . . . . . . . .205

Table 1101.4.6 Materials for Subsoil Drainpipe and Fittings . . . . . . . . . . . . . . . . . .205

1101.5 Expansion Joints Required . . . . . .205

1101.6 Subsoil Drains . . . . . . . . . . . . . . .205

1101.7 Building Subdrains . . . . . . . . . . . .206

1101.8 Areaway Drains . . . . . . . . . . . . . .206

1101.9 Window Areaway Drains . . . . . . .206

1101.10 Filling Stations and Motor Vehicle Washing Establishments . . . . . . . . . . . . . . .206

1101.11 Paved Areas . . . . . . . . . . . . . . . . .206

1101.12 Roof Drainage . . . . . . . . . . . . . . .206

1101.13 Cleanouts . . . . . . . . . . . . . . . . . . .207

1101.14 Rainwater Sumps . . . . . . . . . . . . .207

1101.15 Traps on Storm Drains and Leaders . . . . . . . . . . . . . . . . . . . . .207

1101.16 Leaders, Conductors, and

Connections . . . . . . . . . . . . . . . . .207

1102.0 Roof Drains . . . . . . . . . . . . . . . . . .207

1102.1 Applications . . . . . . . . . . . . . . . . .207

1102.2 Dome Strainers Required . . . . . . .207

1102.3 Roof Drain Flashings . . . . . . . . . .207

1103.0 Size of Leaders, Conductors,

and Storm Drains . . . . . . . . . . . . .207

1103.1 Vertical Conductors and

Leaders . . . . . . . . . . . . . . . . . . . . .207

1103.2 Size of Horizontal Storm

Drains and Sewers . . . . . . . . . . . .207

1103.3 Size of Roof Gutters . . . . . . . . . . .207

1103.4 Side Walls Draining onto a Roof . . . . . . . . . . . . . . . . . .207

Table 1103.1 Sizing Roof Drains, Leaders, and Vertical Rainwater Piping . . .208

1104.0 Values for Continuous Flow . . . . .208

1104.1 General . . . . . . . . . . . . . . . . . . . . .208

1105.0 Controlled-Flow Roof

Drainage . . . . . . . . . . . . . . . . . . . .208
CPC § 1101.16 High relevance — show source text
1101.16 Leaders, Conductors, and Connections. Leaders or conductors shall not be used as soil, waste, or vent pipes nor shall soil, waste, or vent pipes be used as leaders or conductors.

1101.16.1 Protection of Leaders. Leaders installed along alleyways, driveways, or other locations where exposed to damage shall be protected by metal guards, recessed into the wall, or constructed from the ferrous pipe. 1101.16.2 Combining Storm with Sanitary Drainage. The sanitary and storm drainage system of a building shall be entirely separate, except where a combined sewer is used, in which case the building storm drain shall be connected in the same horizontal plane through a single wye fitting to the combined building sewer not less than 10 feet (3048 mm) downstream from a soil stack.

1102.0 Roof Drains.

1102.1 Applications. Roof drains shall be constructed of aluminum, cast-iron, copper alloy of not more than 15 percent zinc, leaded nickel bronze, stainless steel, ABS, PVC, polypropylene, polyethylene, or nylon and shall comply with ASME A112.3.1 or ASME A112.6.4.

1102.2 Dome Strainers Required. Roof drains shall have domed strainers.

Exception: Roof drain strainers for use on sun decks, parking decks, and similar areas that are normally serviced and maintained, shall be permitted to be of the flat surface type. Such roof drain strainers shall be level with the deck.

1102.3 Roof Drain Flashings. The connection between the roof and roof drains that pass through the roof and into the interior of the building shall be made watertight by the use of proper flashing material. 1102.3.1 Lead Flashing. Where lead flashing material is used, it shall be not less than 4 pounds per square foot (lb/ft [2] ) (19 kg/m [2] ). 1102.3.2 Copper Flashing. Where copper flashing material is used, it shall be not less than 12 ounces per square foot (oz/ft [2] ) (3.7 kg/m [2] ).

1103.0 Size of Leaders, Conductors, and Storm Drains.

1103.1 Vertical Conductors and Leaders. Vertical conductors and leaders shall be sized by the maximum projected roof area and Table 1103.1.

1103.2 Size of Horizontal Storm Drains and Sewers. The size of building storm drains, or building storm sewers or their horizontal branches shall be based on the maximum projected roof or paved area to be handled and Table 1103.2.

1103.3 Size of Roof Gutters. The size of semi-circular gutters shall be based on the maximum projected roof area and Table 1103.3.

1103.4 Side Walls Draining onto a Roof. Where vertical walls project above a roof to permit storm water to drain into the roof area below, the adjacent roof area shall be permitted to be computed from Table 1103.1 as follows:

(1) For one wall – add 50 percent of the wall area to the roof area figures.

(2) For two adjacent walls of equal height – add 35 percent of the total wall areas.

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CPC § 407.2.3 High relevance — show source text
LAVATORY FAUCETS

Common and public use areas . . . . . . . . . . . . . .407.2.3 Maximum flow rate . . . . . . . . . . . . . . . . .407.2.1, 407.2.2

Metering faucet . . . . . . . . . . . . . . . . . . . . . . . . . .407.2.4

Public . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .407.2.1

Residential . . . . . . . . . . . . . . . . . . . . . . . . . . . . .407.2.2

LAWN SPRINKLERS . . . . . . . . .Table 610.3, Table A 103.1,

A 103.2, M 102.5

LEAD

Allowable lead contents . . . . . . . . . . . . . .604.2, 604.2.1

Bends and traps . . . . . . . . . . . . . . . . . . . . .701.5, 906.6 Closet rings . . . . . . . . . . . . . . . . . . . . . . . . . . . .402.6.1

Flashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1102.3.1

Roof drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1102.1

Sheet . . . . . . . . . . . . . . . . . . . . . . .408.8.3, 701.5, 906.6

Water supply . . . . . . . . . . . . . . . . . . . . . .604.2, 604.2.1

LEADERS

Cleanouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1101.13

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .214.0

Installed outside . . . . . . . . . . . . . . . . . . . . . . . . .1101.4.3

Leaders, conductors, and connections . . . . . . . .1101.16 Roof drainage . . . . . . . . . . . . . . . . . . . . . . . . . . .1101.12 Size of leaders, conductors, and

storm drains . . . . . . . . . . . . . . . . . . . . . . . . . . .1103.0

Sizing roof drains, leaders, and vertical rainwater piping . . . . . . . . . . . . .Table 1103.1 Traps on storm drains and leaders . . . . . . . . . . .1101.15

LIMITED-DENSITY OWNER-BUILT

RURAL DWELLING

Connections to plumbing system . . . . . . . . . . . . . .304.1
CPC § 1101.11 High relevance — show source text
1101.11 Paved Areas. Where the occupant creates surface water drainage, the sumps, gratings, or floor drains shall be piped to a storm drain or an approved water course. 1101.12 Roof Drainage. Roof drainage shall comply with Section 1101.12.1 and Section 1101.12.2.

1101.12.1 Primary Roof Drainage. Roof areas of a building shall be drained by roof drains or gutters. The location and sizing of drains and gutters shall be coordinated with the structural design and pitch of the roof. Unless otherwise required by the Authority Having Jurisdiction, roof drains, gutters, vertical conductors or leaders, and horizontal storm drains for primary drainage shall be sized based on a storm of 60 minutes duration and 100 year return period. Refer to Table D 101.1 (in Appendix D) for 100 years, 60-minute storms at various locations. 1101.12.2 Secondary Drainage. Secondary (emergency) roof drainage shall be provided by one of the methods specified in Section 1101.12.2.1 or Section 1101.12.2.2.

1101.12.2.1 Roof Scuppers or Open Side. Secondary roof drainage shall be provided by an opensided roof or scuppers where the roof perimeter construction extends above the roof in such a manner that water will be entrapped. An open-sided roof or scuppers shall be sized to prevent the depth of ponding water from exceeding that for which the roof was designed as determined by Section 1101.12.1. Scupper openings shall be not less than 4 inches (102 mm) high and have a width equal to the circumference of the roof drain required for the area served, sized in accordance with Table 1103.1.

1101.12.2.2 Secondary Roof Drain. Secondary roof drains shall be provided. The secondary roof drains shall be located not less than 2 inches (51 mm) above the roof surface. The maximum height of the roof drains shall be a height to prevent the depth of ponding water from exceeding that for which the roof was designed as determined by Section 1101.12.1. The secondary roof drains shall connect to a piping system in accordance with Section 1101.12.2.2.1 or Section 1101.12.2.2.2.

1101.12.2.2.1 Separate Piping System. The secondary roof drainage system shall be a

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STORM DRAINAGE

separate system of piping, independent of the primary roof drainage system. The discharge shall be above grade, in a location observable by the building occupants or maintenance personnel. Secondary roof drain systems shall be sized in accordance with Section 1101.12.1

based on the rainfall rate for which the primary system is sized. 1101.12.2.2.2 Combined System. The secondary roof drains shall connect to the vertical piping of the primary storm drainage conductor downstream of the last horizontal offset located below the roof. The primary storm drainage system shall connect to the building storm water that connects to an underground public storm sewer. The combined secondary and primary roof drain systems shall be sized in accordance with Section 1103.0 based on double the rain fall rate for the local area.
CPC § 1602.6 High relevance — show source text
The test shall be ruled successful by the Authority Having Jurisdiction before final approval is granted. 1602.6 Sizing. The design and size of rainwater drains, gutters, conductors, and leaders shall comply with Chapter 11 of this code.

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NONPOTABLE RAINWATER CATCHMENT SYSTEMS

1602.7 Rainwater Catchment System Materials. Rain- 1603.3 Rainwater Catchment Collection Surfaces. water catchment system materials shall comply with Section Rainwater shall be collected from roof surfaces or other 1602.7.1 through Section 1602.7.3 . impervious manmade, aboveground collection surfaces. 1602.7.1 Water Supply and Distribution Materi- 1603.3.1 Other Surfaces. Natural precipitation colals. Rainwater catchment water supply and distribution lected from surface water runoff, vehicular parking surmaterials shall comply with the requirements of this code faces, or manmade surfaces at or below grade shall be in for potable water supply and distribution systems unless accordance with the water quality requirements for onotherwise provided for in this section. site treated nonpotable gray water systems in Section

1506.0.

1602.7.2 Rainwater Catchment System Drainage Materials. Materials used in rainwater catchment Exception: Collected rainwater or storm water used

exclusively for subsurface landscape irrigation.

drainage systems, including gutters, downspouts, conductors, and leaders shall be in accordance with the 1603.3.2 Prohibited Discharges. Overflows and requirements of this code for storm drainage. bleed-off pipes from roof-mounted equipment and appli ances shall not discharge onto roof surfaces that are

1602.7.3 Storage Tanks. Rainwater storage tanks shall

intended to collect rainwater without prior approval from

comply with Section 1603.5.

the Authority Having Jurisdiction.

1602.8 Rainwater Catchment System Color and

1603.4 Minimum Water Quality. The minimum water

Marking Information. Rainwater catchment systems shall

quality for harvested rainwater shall meet the applicable water

have a colored background in accordance with Section 601.3.

quality requirements for the intended applications as deter Rainwater catchment systems shall be marked, in lettering in

mined by the Authority Having Jurisdiction. In the absence of

accordance with Section 601.3.3, with the words: “CAU water quality requirements determined by the Authority Hav TION: NONPOTABLE RAINWATER, DO NOT DRINK.”

ing Jurisdiction, the minimum treatment and water quality
CPC § 408.8.3 High relevance — show source text
Sheet . . . . . . . . . . . . . . . . . . . . . . .408.8.3, 701.5, 906.6

Water supply . . . . . . . . . . . . . . . . . . . . . .604.2, 604.2.1

LEADERS

Cleanouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1101.13

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .214.0

Installed outside . . . . . . . . . . . . . . . . . . . . . . . . .1101.4.3

Leaders, conductors, and connections . . . . . . . .1101.16 Roof drainage . . . . . . . . . . . . . . . . . . . . . . . . . . .1101.12 Size of leaders, conductors, and

storm drains . . . . . . . . . . . . . . . . . . . . . . . . . . .1103.0

Sizing roof drains, leaders, and vertical rainwater piping . . . . . . . . . . . . .Table 1103.1 Traps on storm drains and leaders . . . . . . . . . . .1101.15

LIMITED-DENSITY OWNER-BUILT

RURAL DWELLING

Connections to plumbing system . . . . . . . . . . . . . .304.1

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .214.0

Disposal of liquid waste . . . . . . . . . . . . . . . . . . . . .303.1 Water supply and flushing . . . . . . . . . . . . . . . . . . .601.2 LIQUEFIED PETROLEUM

GAS (LP-GAS) . . . . . . . . . . . . . . . 214.0, 1202.1, 1208.4.1,

1208.5.6.3, 1208.5.10.4,

1212.11, E 401.2,

E 403.1, E 403.10

LIQUID WASTES . . . . . . . . . . . . . . . . .214.0, 303.0, L 302.0

LISTED . . . . . . . . . . . . . . . . . . . . . . . .214.0, 301.2, 402.6.2,

501.1

LISTING AGENCY . . . . . . . . . . . . . . . . . . . . . . .214.0, 301.2

LOCATION OF

Backwater valves . . . . . . . . .710.1, 710.3, 710.4, 710.6,

1006.0, 1101.6.4, 1503.2.3,

1503.9.1, 1503.9.7
CPC § 1101.7 High relevance — show source text
(1) They do not serve continuously flowing springs or groundwater.

(2) The point of discharge is not less than 10 feet (3048 mm) from a property line.

(3) It is impracticable to discharge such drains to a storm drain, to an approved water course, to the front street curb or gutter, or to an alley. 1101.7 Building Subdrains. Building subdrains located below the public sewer level shall discharge into a sump or receiving tank, the contents of which shall be automatically lifted and discharged into the drainage system as required for building sumps. 1101.8 Areaway Drains. Open subsurface space adjacent to a building, serving as an entrance to the basement or cellar of a building, shall be provided with a drain or drains. The areaway drains shall be not less than 2 inches (50 mm) in diameter for areaways at a maximum of 100 square feet (9.29 m [2] ) in area, and shall be discharged in the manner provided for subsoil drains not serving continuously flowing springs or groundwater (see Section 1101.6.1). Areaways exceeding 100 square feet (9.29 m [2] ) shall not drain into subsoil drains.

The drains for areaways exceeding 100 square feet (9.29 m [2] ) shall be sized in accordance with Table 1103.2.

1101.9 Window Areaway Drains. Window areaways at a maximum of 10 square feet (0.93 m [2] ) in area shall be permitted to discharge to the subsoil drains through a 2 inch (50 mm) diameter pipe. However, window areaways exceeding 10 square feet (0.93 m [2] ) in area shall be handled in the manner provided for entrance areaways (see Section 1101.8). 1101.10 Filling Stations and Motor Vehicle Washing Establishments. Public filling stations and motor vehicle washing establishments shall have the paved area sloped toward sumps or gratings within the property lines. Curbs not less than 6 inches (152 mm) high shall be placed where required to direct water to gratings or sumps.

1101.11 Paved Areas. Where the occupant creates surface water drainage, the sumps, gratings, or floor drains shall be piped to a storm drain or an approved water course. 1101.12 Roof Drainage. Roof drainage shall comply with Section 1101.12.1 and Section 1101.12.2.

1101.12.1 Primary Roof Drainage. Roof areas of a building shall be drained by roof drains or gutters. The location and sizing of drains and gutters shall be coordinated with the structural design and pitch of the roof. Unless otherwise required by the Authority Having Jurisdiction, roof drains, gutters, vertical conductors or leaders, and horizontal storm drains for primary drainage shall be sized based on a storm of 60 minutes duration and 100 year return period. Refer to Table D 101.1 (in Appendix D) for 100 years, 60-minute storms at various locations. 1101.12.2 Secondary Drainage. Secondary (emergency) roof drainage shall be provided by one of the methods specified in Section 1101.12.2.1 or Section 1101.12.2.2.
CPC § 2.4 High relevance — show source text
The vent terminal shall be directed downward and covered with a [3] ⁄ 32 of an inch (2.4 mm) mesh screen to prevent the entry of vermin and insect.

K 105.11 Pumps. Pumps serving rainwater catchment systems shall be listed for potable water use. Pumps supplying water to water closets, urinals, and trap primers shall be capable of delivering not less than the minimum residual pressure required by the highest and most remote outlet served. Where the water pressure in the rainwater supply system within the building exceeds 80 psi (552 kPa), a pressure reducing valve reducing the pressure to 80 psi (552 kPa) or less to water outlets in the building shall be installed in accordance with this code.

K 105.12 Roof Drains. Primary and secondary roof drains, conductors, leaders, overflows, and gutters shall be designed and installed in accordance with this code.

K 106.0 Freeze Protection.

K 106.1 General. Tanks and piping installed in locations subject to freezing shall be provided with an approved means of freeze protection. K 106.2 Roof Washer or Pre-Filtration System. Collected rainwater shall pass through a roof washer or pre-filtration system before the water enters the rainwater storage tank. Roof washer systems shall comply with Section K 106.2.1 through Section K 106.2.4.

K 106.2.1 Size. The roof washer shall be sized to direct rainwater containing debris that has accumulated on the collection surface away from the storage tank. ARCSA/ASPE/ANSI 63 contains additional guidance on acceptable methods of sizing roof washers.

K 106.2.2 Debris Screen. The inlet to the roof washer shall be provided with a debris screen or other approved means that protects the roof washer from the intrusion of debris and vermin. Where the debris screen is installed, the debris screen shall be corrosion resistant and shall have openings not larger than [1] ⁄ 2 of an inch (12.7 mm). K 106.2.3 Drain Discharge. Water drained from the roof washer, or pre-filter shall be diverted away from the storage tank and discharged to a disposal area that does not cause property damage or erosion. Roof washer drainage shall not drain over a public way. K 106.2.4 Automatic Drain. Roof washing systems shall be provided with an automatic means of self-draining between rain events.

K 106.3 Roof Gutters. Gutters shall maintain a minimum slope and be sized in accordance with this code. K 106.4 Drains, Conductors, and Leaders. The design and size of rainwater drains, conductors, and leaders shall comply with this code. K 106.5 Size of Potable Water Piping. Potable rainwater system distribution piping shall be sized in accordance with this code for sizing potable water piping.

K 107.0 Cleaning. K 107.1 General. The interior surfaces of tanks and equipment shall be clean before they are put into service.

Frequently asked questions

What rainfall event does the CPC use to size primary roof drainage?

Primary roof drainage is typically sized for a 60‑minute duration, 100‑year return‑period storm, as required by §1101.12; secondary/emergency drainage must be provided per the same section and may require doubled rainfall rates when combined with primary systems .

Where are the sizing tables for leaders, gutters and horizontal storm piping?

Use Table 1103.1 for vertical leaders and roof drains, Table 1103.2 for horizontal storm drains/sewers, and Table 1103.3 for gutters; these are referenced in §1103.0 and adjacent text in Chapter 11 .

When can I use a controlled‑flow or engineered storm drainage system?

Controlled‑flow roof drainage is covered in §1105.0 with maximum allowable ponding depths and scupper distances in Tables 1105.1(1) and 1105.1(2); engineered systems (including siphonic systems) are permitted when designed by a registered design professional and approved per §1106.0 .

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Related in the CPC

General requirements & materials for storm drainage

Roof drains, gutters, scuppers and secondary (emergency) drainage

Engineered storm systems, siphonic drains and testing

Storm Drainage

California Plumbing Code