CPC · California Plumbing Code
Leader, downspout and other roof drainage terms
A leader (downspout) is the exterior vertical pipe that conveys roof stormwater to a storm drain or other discharge; the CPC requires leaders be sized by projected roof area (Table 1103.1), have a cleanout at their base, be trapped when tied into combined sewers, be protected where exposed, and use domed strainers on roof drains — see Chapter 11 provisions such as **§ 1101.13.1**, **§ 1101.15**, **§ 1101.16**, **§ 1102.2**, and **§ 1103.1** for the detailed rules.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
The California Plumbing Code treats roof drainage components by name and function: Leader, Downspout, Conductor, and Roof Drain are defined and then regulated by the storm-drainage rules in Chapter 11. Key installation controls are sizing, protection, cleanouts, traps for combined sewers, and scupper/secondary-drain requirements. See § 1101.13.1, § 1101.15, § 1101.16, § 1102.2, and § 1103.1 for the operative provisions used below.
Note: the user-requested controlling section § 215.0 was not present in the files I was able to retrieve. I therefore ground all specific requirements below in the Chapter 11 (storm drainage) and definitions material that is available in the provided CPC file excerpts. If you specifically need text from § 215.0, I can fetch it if you upload that page or allow another search.
A leader (rain leader/downspout) is the exterior vertical pipe that carries roof-collected stormwater into a building storm drain, combined sewer, or to an approved discharge point — and it must be sized, trapped (when required), provided with cleanouts, and protected where exposed, per Chapter 11.
Requirements in detail
Short definitions (first use bolded)
- Leader — an exterior vertical drainage pipe conveying storm water from roof or gutter drains. See Downspout. § 211.0 (Leader definition).
- Downspout — the rain leader from the roof to the building storm drain, combined building sewer, or other means of disposal located outside the building. See Conductor and Leader. § (Downspout definition).
- Roof Drain — a drain installed to receive water collecting on a roof surface and discharge into a leader, downspout, or conductor. § (Roof Drain definition).
(Definitions above are taken from the CPC definitions pages available in the uploaded file set.)
Basic installation & layout rules (by topic)
- Cleanouts: install a cleanout at the base of any rain leader or conductor before it connects to the horizontal building storm drain. § 1101.13.1.
- Traps: Where a leader or storm drain connects to a combined sewer, the leader or the main storm drain must be trapped; traps on leaders shall be the same size as the horizontal drain they serve. § 1101.15, § 1101.15.2, § 1101.15.3.
- Exception: no trap is required for leaders/conductors connected to a sewer carrying storm water exclusively, or where roof inlets are permitted by vent termination rules. § 1101.15.1 and exception language.
- Use limitation: Leaders and conductors shall not be used as soil, waste, or vent pipes, nor shall soil, waste or vent pipes be used as leaders/conductors. § 1101.16.
- Protection from damage: leaders exposed to vehicle or other mechanical damage (alleys, driveways) must be protected with metal guards, recessed mounts, or be of ferrous pipe. § 1101.16.1.
- Roof drains: Roof drains must have domed strainers (flat strainers only permitted on certain serviceable decks). § 1102.2.
- Secondary (emergency) roof drainage: Secondary roof drains must be provided by scuppers/open sided roof or dedicated secondary drains sized per primary design rules; secondary drains located not less than 2 inches above the roof surface. § 1101.12.2, § 1101.12.2.2.
Sizing and design reference rules
- Sizing drivers: Vertical conductors, leaders and downspouts are sized by the maximum projected roof area served and Table 1103.1; horizontal storm drains are sized by Table 1103.2; gutters by 1103.3. § 1103.1, § 1103.2, § 1103.3.
- Controlled-flow roof design: When a controlled-flow (stored water) roof system is used, the permitted maximum water depth at the drain depends on roof rise; see Table 1105.1(1) (examples in the CPC: Flat = 3 in, 2 in rise = 4 in, 4 in rise = 5 in, 6 in rise = 6 in) and associated design notes. § 1105.1 / Table 1105.1(1).
- Catchment & rainwater systems: rainwater catchment drains/gutters/leaders used for rainwater collection must follow the CPC storm drainage rules; sizing design and materials cross-reference Chapter 11. § 1602.6, § 1602.7.2.
Quick decision table (values, thresholds, code reference)
| Decision item | Rule / Value | Code Reference |
|---|---|---|
| Cleanout at base of leader/conductor | Required before connection to horizontal drain | § 1101.13.1 |
| Trapping when connected to combined sewer | Leaders/storm drains must be trapped; trap size = same as horizontal drain | § 1101.15, § 1101.15.2 |
| Where no trap required | Sewers carrying storm water exclusively; certain vent termination locations | § 1101.15.1; exception text |
| Secondary roof drain elevation | Not less than 2 inches above roof surface | § 1101.12.2.2 |
| Minimum scupper height | Scupper openings not less than 4 inches high | § 1101.12.2.1 |
| Roof drain strainers | Domed strainers required (flat permitted for serviceable decks) | § 1102.2 |
| Controlled-flow max water depth (examples) | Flat = 3 in; 2 in rise = 4 in; 4 in rise = 5 in; 6 in rise = 6 in | Table 1105.1(1) / § 1105.1 |
| Sizing reference | Leaders/conductors sized by projected roof area using Table 1103.1 | § 1103.1 |
Exceptions & special cases
- Combined sewer situations: When a building uses a combined building sewer, the CPC requires traps on leaders/storm drains (or a single trap on main before combined sewer). See § 1101.15.3 for installation method and cleanout requirements.
- Storm-only sewers: No traps when the sewer carries only storm water (§ 1101.15.1).
- Roof-strainer exceptions: Flat/parking/sun decks may use flat strainers if regularly serviced; otherwise domed strainers are required. § 1102.2.
- Secondary drainage alternatives: Secondary drainage may be scuppers/open sides sized to avoid ponding, OR secondary roof drains connected to a separate system or combined downstream as described in § 1101.12.2.1–.2.2.
Common mistakes
- Treating a leader as a soil/waste/vent pipe (or vice versa). The code explicitly forbids this. § 1101.16.
- Omitting the required cleanout at the base of an exterior leader before the horizontal storm drain connection. § 1101.13.1.
- Forgetting to trap connections to a combined sewer (or installing incorrectly sized traps). § 1101.15 and § 1101.15.2.
- Using flat strainers on unsupervised roofs (flat strainers only permitted for serviceable decks). § 1102.2.
- Sizing leaders only by roof length instead of projected roof area per Table 1103.1. Always use the projected roof area method. § 1103.1.
Worked example — single-family roof to leader/downspout
Scenario: A house has a simple rectangular roof with a projected roof area of 1,200 ft² that drains to a single leader/downspout located at a corner. Local design uses CPC Chapter 11 sizing tables.
Steps (what the CPC requires):
- Determine leader size from projected roof area using Table 1103.1 and the local rainfall rate per § 1103.1. (Table 1103.1 is the sizing table for vertical conductors and leaders; the CPC directs this method.) § 1103.1.
- Provide a cleanout at the base of the leader before it connects to the horizontal building storm drain. § 1101.13.1.
- If the building storm sewer is combined with sanitary sewer (combined sewer), install a trap sized equal to the horizontal drain or follow the single-trap option in § 1101.15.3. If it is storm-only, no trap is required per § 1101.15.1.
- Protect the leader if it’s exposed to vehicles (e.g., along a driveway) with guards or use ferrous pipe per § 1101.16.1.
Note: I cannot quote the numerical leader pipe diameter directly here because the table entries (Table 1103.1) and the local rainfall intensity together determine the allowable roof area per pipe size. The CPC requires you to use Table 1103.1 with the local rainfall rate to pick the correct pipe size. § 1103.1.
Related provisions
- § 1101.12.1 — Primary roof drainage sizing and basis for storm event (60-minute, 100-year default unless AHJ says otherwise).
- § 1101.12.2 — Secondary (emergency) roof drainage rules (scuppers or secondary drains).
- § 1102.1 / § 1102.2 — Roof drain construction and domed strainer requirement.
- § 1103.1 / Table 1103.1 — Sizing vertical conductors, leaders, and downspouts by projected roof area.
- § 1103.2 / Table 1103.2 — Sizing horizontal storm drains.
- § 1105.1 / Table 1105.1(1) — Controlled-flow maximum roof water depth values and rules.
- § 1101.13.1 — Cleanouts for rain leaders and conductors.
- § 1101.15 — Traps on leaders and storm drains when connected to combined sewer.
- § 1602.6 — Rainwater system sizing cross-reference to Chapter 11.
Code references
Grounded in the retrieved California Plumbing Code — click a citation to read the verbatim passage:
CPC § 207.0 High relevance — show source text
Disposal Field. [BSC-CG & HCD 1] An intended desti- nation for gray water, including but not limited to, a mulch basin or receiving landscape feature, gray water leach field, or other approved method of disposal.
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DEFINITIONS
Domestic Sewage. The liquid and water-borne wastes derived from the ordinary living processes, free from industrial wastes, and of such character as to permit satisfactory disposal, without special treatment, into the public sewer or by means of a private sewage disposal system.
Downspout. The rain leader from the roof to the building storm drain, combined building sewer, or other means of disposal located outside of the building. See Conductor and Leader.
Drain. A pipe that carries waste or waterborne wastes in a building drainage system. Drainage System. Includes all the piping within public or private premises that conveys sewage, storm water, or other liquid wastes to a legal point of disposal, but does not include the mains of a public sewer system or a public sewage treatment or disposal plant.
Drinking Fountain. A plumbing fixture connected to the potable water distribution system and sanitary drainage system that provides drinking water in a flowing stream so that the user can consume water directly from the fixture without the use of accessories. Drinking fountains should also incorporate a bottle filling station and can incorporate a water filter and a cooling system for chilling the drinking water.
Dry Vent. A vent that does not receive the discharge of any sewage or waste. Durham System. Soil or waste system in which all piping is threaded pipe, tubing, or other such rigid construction, using recessed drainage fittings to correspond to the types of piping.
207.0 – E –
Effective Ground-Fault Current Path. An intentionally constructed, low impedance electrically conductive path designed and intended to carry current under ground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground-fault detectors. [NFPA 70:100]
Effective Opening. The minimum cross-sectional area at the point of water supply discharge measured or expressed in terms of (1) diameter of a circle or (2) where the opening is not circular, the diameter of a circle of equivalent cross-sectional area. (This applies to an air gap).
Emergency Floor Drain. A floor drain that does not receive discharge from any fixture drain or indirect waste pipe, and serves to protect from damage where accidental spills, leaks or fixture backups occur.
Enforcing Agency. [BSC, BSC-CG, HCD 1, HCD 2 & HCD 1-AC] “Enforcing Agency” is the designated depart- ment or agency as specified by statute or regulation.
Essentially Nontoxic Transfer Fluid. A fluid generally recognized as safe by the Food and Drug Administration (FDA) as food grade. Exam Room Sink. A sink used in the patient exam room of a medical or dental office with a primary purpose of the washing of hands.
CPC § 207.0 High relevance — show source text
Department Having Jurisdiction. The Authority Having Jurisdiction, including any other law enforcement agency affected by a provision of this code, whether such agency is specifically named or not.
[HCD 1 & HCD 2] “Department Having Jurisdiction” shall mean “Enforcing Agency” as defined in Section 207.0 of this code.
Design Flood Elevation. The elevation of the “design flood,” including wave height, relative to the datum specified on the community’s legally designated flood hazard map. In areas designated as Zone AO, the design flood elevation is the elevation of the highest existing grade of the building’s perimeter plus the depth number (in feet) specified on the flood hazard map. In areas designated as Zone AO where a depth number is not specified on the map, the depth number is taken as being equal to 2 feet (610 mm).
Developed Length. The length along the centerline of a pipe and fittings.
Diameter. Unless specifically stated, “diameter” is the nominal diameter as designated commercially.
Direct-Vent Appliances. Appliances that are constructed and installed so that all air for combustion is derived directly from the outdoors and all flue gases are discharged to the outdoors. [NFPA 54:3.3.4.2]
Disinfected Tertiary Recycled Water. [DWR] Filtered and subsequently disinfected wastewater that meets the approved method of treatment and minimum level of water quality specified in California Code of Regulations, Title 22, Division 4, Chapter 3 for the purpose of direct beneficial use.
Disposal Field. [BSC-CG & HCD 1] An intended desti- nation for gray water, including but not limited to, a mulch basin or receiving landscape feature, gray water leach field, or other approved method of disposal.
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DEFINITIONS
Domestic Sewage. The liquid and water-borne wastes derived from the ordinary living processes, free from industrial wastes, and of such character as to permit satisfactory disposal, without special treatment, into the public sewer or by means of a private sewage disposal system.
Downspout. The rain leader from the roof to the building storm drain, combined building sewer, or other means of disposal located outside of the building. See Conductor and Leader.
Drain. A pipe that carries waste or waterborne wastes in a building drainage system. Drainage System. Includes all the piping within public or private premises that conveys sewage, storm water, or other liquid wastes to a legal point of disposal, but does not include the mains of a public sewer system or a public sewage treatment or disposal plant.
Drinking Fountain. A plumbing fixture connected to the potable water distribution system and sanitary drainage system that provides drinking water in a flowing stream so that the user can consume water directly from the fixture without the use of accessories. Drinking fountains should also incorporate a bottle filling station and can incorporate a water filter and a cooling system for chilling the drinking water.
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 § 1101.12.2.2 High relevance — show source text
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.
1101.13 Cleanouts. Cleanouts for building storm drains shall comply with the requirements of Section 719.0 of this code.
1101.13.1 Rain Leaders and Conductors. Rain leaders and conductors connected to a building storm sewer shall have a cleanout installed at the base of the
leader or conductor before it connects to the horizontal
drain.
1101.14 Rainwater Sumps. Rainwater sumps serving “public use” occupancy buildings shall be provided with dual pumps arranged to function alternately in the case of overload or mechanical failure. Pumps rated 600 V or less shall comply with UL 778 and shall be installed in accordance with the manufacturer’s installation instructions.
1101.15 Traps on Storm Drains and Leaders. Leaders and storm drains, where connected to a combined sewer, shall be trapped. Floor and area drains connected to a storm drain shall be trapped.
Exception: Traps shall not be required where roof drains, rain leaders, and other inlets are at locations permitted under Section 906.0, Vent Termination.
1101.15.1 Where Not Required. No trap shall be required for leaders or conductors that are connected to a sewer carrying storm water exclusively. 1101.15.2 Trap Size. Traps, where installed for individual conductors, shall be the same size as the horizontal drain to which they are connected.
1101.15.3 Method of Installation of Combined Sewer. Individual storm-water traps shall be installed on the stormwater drain branch serving each storm-water inlet, or a single trap shall be installed in the main storm drain just before its connection with the combined building sewer. Such traps shall be provided with an accessible cleanout on the outlet side of the trap.
CPC § 221.0 High relevance — show source text
Recycled Water Supply System. [DWR] The building supply pipe, the water distribution pipes, and the necessary connecting pipes, fittings, control valves, backflow preven- tion devices, and all appurtenances carrying or supplying reclaimed (recycled) water in or adjacent to the building or within the premises.
Registered Design Professional. An individual who is registered or licensed by the laws of the state to perform such design work in the jurisdiction.
Regulating Equipment. Includes valves and controls used in a plumbing system that is required to be accessible or readily accessible.
Relief Vent. A vent, the primary function of which is to provide circulation of air between drainage and vent systems or to act as an auxiliary vent on a specially designed system.
Remote Outlet. Where used for sizing water piping, it is the furthest outlet dimension, measuring from the meter, either the developed length of the cold-water piping or through the water heater to the furthest outlet on the hot-water piping.
Rim. See Flood-Level Rim.
Riser. A water supply pipe that extends vertically one full story or more to convey water to branches or fixtures.
Roof Drain. A drain installed to receive water collecting on the surface of a roof and to discharge it into a leader, downspout, or conductor.
Roof Washer. A device or method for removal of sediment
and debris from a collection surface by diverting initial rainfall from entry into the cistern(s). Also, known as a first flush device.
Roughing-In. The installation of all parts of the plumbing system that can be completed prior to the installation of fixtures. This includes drainage, water supply, gas piping, vent piping, and the necessary fixture supports.
221.0 – S –
Sand Interceptor. See Interceptor (Clarifier).
Scavenging. Evacuation of exhaled mixtures of oxygen and nitrous oxide. [NFPA 99:3.3.163]
Scrub Sink. [OSHPD 1, 2, 3, 4 & 5] Is a sink used to wash and scrub the hands and arms during the septic preparation
for surgery and equipped with a supply spout as required for a handwashing fixture. The scrub sink shall be trimmed with foot, knee or electronic sensor controls that do not involve contact with the upper extremities. Sensor operated fixtures shall be capable of functioning during loss of normal power. Single-lever wrist blades shall not be permitted except for the temperature pre-set valve.
SDR. An abbreviation for “standard dimensional ratio,” which is the specific ratio of the average specified outside diameter to the minimum wall thickness for outside controlled
diameter plastic pipe.
Seam, Welded. See Joint, Welded.
Seepage Pit. A lined excavation in the ground which receives the discharge of a septic tank so designed as to permit the effluent from the septic tank to seep through its bottom and sides.
Septic Tank. A watertight receptacle that receives the discharge of a drainage system or part thereof, designed and constructed so as to retain solids, digest organic matter through a period of detention, and allow the liquids to discharge into the soil outside of the tank through a system of open joint piping or a seepage pit meeting the requirements of this code.
CPC § 4-11 Medium relevance — show source text
(Equation A4.4-11) Weight of material (percent) = [Weight of material (lbs) ÷ Weight of assembly (lbs)] × 100 (See Equation A4.4-7) RC M (percent) = Postconsumer content percentage + ( [1] / 2 ) Preconsumer content percentage
Method 2: Recycled content (postconsumer and preconsumer) provided in pounds
(Equation A4.4-12) PRC M (percent) = [RC M (lbs) ÷ Weight of material (lbs)] × 100 (Equation A4.4-13) RC M (lbs) = Postconsumer content (lbs) + ( [1] / 2 ) Preconsumer content (lbs)
Note: If the manufacturer reports total recycled content of a material as one percentage in lieu of separately reporting preconsumer and postconsumer values, the total shall be considered preconsumer recycled material.
A4.405.3.1.5 Alternate method for concrete. When Supplementary Cementitious Materials (SCMs), such as fly ash or ground blast furnace slag cement, are used in concrete, an alternate method of calculating and reporting recycled content in concrete products shall be permitted. When determining the recycled content value, the percent recycled content shall be multiplied by the cost of the cementitious materials only, not the total cost of the concrete.
A4.405.4 Use of building materials from rapidly renewable sources. One or more of the following materials manufactured from rapidly renewable sources or agricultural by-products is used:
Insulation.
Bamboo or cork.
Engineered products.
Agricultural based products.
Other products acceptable to the enforcing agency.
Note: The intent of this section is to utilize building materials and products which are typically harvested within a 10-year or shorter cycle.
SECTION A4.406—ENHANCED DURABILITY AND REDUCED MAINTENANCE (RESERVED)
SECTION A4.407—WATER RESISTANCE AND MOISTURE MANAGEMENT
A4.407.1 Drainage around foundations. Install foundation and landscape drains which discharge to a dry well, sump, bioswale or other approved on-site location.
A4.407.2 Roof drainage. Install gutter and downspout systems to route water at least 5 feet away from the foundation or connect to landscape drains which discharge to a dry well, sump, bioswale, rainwater capture system or other approved on-site location.
A4.407.3 Flashing details. Provide flashing details on the building plans which comply with accepted industry standards or manufacturer’s instructions. Details are shown on house plans at all of the following locations:
Around windows and doors.
Roof valleys.
Deck connections to the structure.
Roof-to-wall intersections.
Chimneys to roof intersections.
Drip caps above windows and doors with architectural projections.
Note: Reference details may be found in the Residential Sheet Metal Guidelines published by the Sheet Metal and Air Conditioning Contractors’ National Association Inc.
A4.407.4 Material protection. Protect building materials delivered to the construction site from rain and other sources of moisture.
A4.407.5 Ice and water barriers. In Climate Zone 16, an ice and water barrier is installed at valley, eaves and wall to roof intersections. The ice and water barrier shall extend at least 24 inches inside the exterior wall line or as specified by the manufacturer’s installation instructions.
CPC § 220.0 Medium relevance — show source text
220.0 – R –
Rainwater. [BSC-CG & HCD 1] Precipitation on any pub- lic or private parcel that has not entered an offsite storm drain system or channel, a flood control channel, or any other stream channel, and has not previously been put to beneficial use. Rainwater Catchment System. [BSC-CG & HCD 1] A facility designed to capture, retain, and store rainwater flow- ing off a building, parking lot, or any other manmade imper- vious surface for subsequent onsite use. Rainwater catchment system is also known as “Rainwater Harvesting System” or “Rainwater Capture System.” Rainwater Storage Tank. The central component of the rainwater catchment system. Also, known as a cistern or rain barrel.
2025 CALIFORNIA PLUMBING CODE 41
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DEFINITIONS
Receiving Landscape. [BSC-CG & HCD 1] Includes features such as soil, basins, swales, mulch, and plants.
Receptor. An approved plumbing fixture or device of such material, shape, and capacity as to adequately receive the discharge from indirect waste pipes, so constructed and located as to be readily cleaned.
Reclaimed (Recycled) Water. [BSC-CG, HCD 1 & DWR] Nonpotable water that meets California State Water Resources Control Board statewide uniform criteria for dis- infected tertiary recycled water. Reclaimed (recycled) water is also known as “recycled water” or “reclaimed water”.
Recycled Water Supply System. [DWR] The building supply pipe, the water distribution pipes, and the necessary connecting pipes, fittings, control valves, backflow preven- tion devices, and all appurtenances carrying or supplying reclaimed (recycled) water in or adjacent to the building or within the premises.
Registered Design Professional. An individual who is registered or licensed by the laws of the state to perform such design work in the jurisdiction.
Regulating Equipment. Includes valves and controls used in a plumbing system that is required to be accessible or readily accessible.
Relief Vent. A vent, the primary function of which is to provide circulation of air between drainage and vent systems or to act as an auxiliary vent on a specially designed system.
Remote Outlet. Where used for sizing water piping, it is the furthest outlet dimension, measuring from the meter, either the developed length of the cold-water piping or through the water heater to the furthest outlet on the hot-water piping.
Rim. See Flood-Level Rim.
Riser. A water supply pipe that extends vertically one full story or more to convey water to branches or fixtures.
Roof Drain. A drain installed to receive water collecting on the surface of a roof and to discharge it into a leader, downspout, or conductor.
Roof Washer. A device or method for removal of sediment
and debris from a collection surface by diverting initial rainfall from entry into the cistern(s). Also, known as a first flush device.
CPC § 1101.13.1 Medium relevance — show source text
1101.13.1 Rain Leaders and Conductors. Rain leaders and conductors connected to a building storm sewer shall have a cleanout installed at the base of the
leader or conductor before it connects to the horizontal
drain.
1101.14 Rainwater Sumps. Rainwater sumps serving “public use” occupancy buildings shall be provided with dual pumps arranged to function alternately in the case of overload or mechanical failure. Pumps rated 600 V or less shall comply with UL 778 and shall be installed in accordance with the manufacturer’s installation instructions.
1101.15 Traps on Storm Drains and Leaders. Leaders and storm drains, where connected to a combined sewer, shall be trapped. Floor and area drains connected to a storm drain shall be trapped.
Exception: Traps shall not be required where roof drains, rain leaders, and other inlets are at locations permitted under Section 906.0, Vent Termination.
1101.15.1 Where Not Required. No trap shall be required for leaders or conductors that are connected to a sewer carrying storm water exclusively. 1101.15.2 Trap Size. Traps, where installed for individual conductors, shall be the same size as the horizontal drain to which they are connected.
1101.15.3 Method of Installation of Combined Sewer. Individual storm-water traps shall be installed on the stormwater drain branch serving each storm-water inlet, or a single trap shall be installed in the main storm drain just before its connection with the combined building sewer. Such traps shall be provided with an accessible cleanout on the outlet side of the trap.
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.
CPC § 1103.1 Medium relevance — show source text
(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
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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)
Flat3
24
45
66 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
CPC § 1103.0 Medium 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 PIPEFLOW 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 § 407.1 Medium relevance — show source text
SECTION A4.406—ENHANCED DURABILITY AND REDUCED MAINTENANCE (RESERVED)
SECTION A4.407—WATER RESISTANCE AND MOISTURE MANAGEMENT
A4.407.1 Drainage around foundations. Install foundation and landscape drains which discharge to a dry well, sump, bioswale or other approved on-site location.
A4.407.2 Roof drainage. Install gutter and downspout systems to route water at least 5 feet away from the foundation or connect to landscape drains which discharge to a dry well, sump, bioswale, rainwater capture system or other approved on-site location.
A4.407.3 Flashing details. Provide flashing details on the building plans which comply with accepted industry standards or manufacturer’s instructions. Details are shown on house plans at all of the following locations:
Around windows and doors.
Roof valleys.
Deck connections to the structure.
Roof-to-wall intersections.
Chimneys to roof intersections.
Drip caps above windows and doors with architectural projections.
Note: Reference details may be found in the Residential Sheet Metal Guidelines published by the Sheet Metal and Air Conditioning Contractors’ National Association Inc.
A4.407.4 Material protection. Protect building materials delivered to the construction site from rain and other sources of moisture.
A4.407.5 Ice and water barriers. In Climate Zone 16, an ice and water barrier is installed at valley, eaves and wall to roof intersections. The ice and water barrier shall extend at least 24 inches inside the exterior wall line or as specified by the manufacturer’s installation instructions.
2025 CALIFORNIA GREEN BUILDING STANDARDS CODE APPENDIX A4-17
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
APPENDIX A4 — RESIDENTIAL VOLUNTARY MEASURES
A4.407.6 Door protection. Exterior doors to the dwelling are covered to prevent water intrusion by one or more of the following:
An awning at least 4 feet in depth is installed.
The door is protected by a roof overhang at least 4 feet in depth.
The door is recessed at least 4 feet.
Other methods which provide equivalent protection.
A4.407.7 Roof overhangs. A permanent overhang or awning at least 2 feet in depth is provided at all exterior walls.
SECTION A4.408—CONSTRUCTION WASTE REDUCTION, DISPOSAL AND RECYCLING
A4.408.1 Enhanced construction waste reduction. Nonhazardous construction and demolition debris generated at the site is diverted to recycle or salvage in compliance with one of the following:
Tier 1. At least a 65 percent reduction. Any mixed recyclables that are sent to mixed-waste recycling facilities shall include a qualified third party verified facility average diversion rate. Verification of diversion rates shall meet minimum certification eligibility guidelines, acceptable to the local enforcing agency.
Tier 2. At least a 75 percent reduction with a third-party verification as required for Tier 1.
Exceptions:
- Equivalent or alternative waste reduction methods are developed by working with local agencies if diversion or recycle facilities capable of compliance with this item do not exist.
- The enforcing agency may make exceptions to the requirements of this section when jobsites are located in areas beyond the haul boundaries of the diversion facility.
CPC § 17958.2. Medium relevance — show source text
(3) A plumbing fixture or other waste discharging receptor or device that is not supplied with water sufficient to flush and maintain the fixture or receptor in a clean condition.
(4) A defective fixture, trap, pipe, or fitting.
(5) A trap, except where in this code exempted, directly connected to a drainage system, the seal of which is not protected against siphonage and backpressure by a vent pipe.
(6) A connection, cross-connection, construction, or condition, temporary or permanent that would permit or make possible by any means whatsoever for an unapproved foreign matter to enter a water distribution system used for domestic purposes.
(7) The preceding enumeration of conditions to which the term “insanitary” shall apply, shall not preclude the application of that term to conditions that are, in fact, insanitary.
2025 CALIFORNIA PLUMBING CODE 37
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DEFINITIONS
that maintains a periodic inspection program of production of labeled products, installations, equipment, or materials and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.
Lavatories in Sets. Two or three lavatories that are served by one trap. Lavatory. [HCD 1 & HCD 2] “Lavatory” shall mean a plumbing fixture used for washing the hands, arms, face and head.
Leader. An exterior vertical drainage pipe for conveying storm water from roof or gutter drains. See Downspout. Limited-Density Owner-Built Rural Dwelling. [HCD 1] “Limited-density owner-built rural dwelling” shall mean any structure consisting of one or more habitable rooms intended or designed to be occupied by one family with facilities for living or sleeping, with use restricted to rural areas desig- nated by local jurisdiction in compliance with the require- ments of Health and Safety Code Section 17958.2. Liquefied Petroleum Gas (LP-Gas) Facilities. Liquefied petroleum gas (LP-Gas) facilities include tanks, containers, container valves, regulating equipment, meters, appurtenances, or any combination thereof for the storage and supply of liquefied petroleum gas for a building, structure, or premises. Liquid Waste. The discharge from a fixture, appliance, or appurtenance in connection with a plumbing system that does not receive fecal matter.
Listed. [HCD 1 & HCD 2] “Listed” means all products that appear in a list published by an approved testing or listing agency. For additional information, see Health and Safety Code Section 17920(h). Listed (Third-Party Certified). Equipment or materials included in a list published by a listing agency (accredited conformity assessment body) that maintains periodic inspection of current production of listed equipment or materials and whose listing states either that the equipment or material complies with approved standards or has been tested and found suitable for use in a specified manner. Listing Agency. An agency accredited by an independent and authoritative conformity assessment body to operate a material and product listing and labeling (certification) system and that are accepted by the Authority Having Jurisdiction, which is in the business of listing or labeling.
CPC § 1014.2.1. Medium relevance — show source text
(2) External flow control, without air intake (vent), directly connected.
(3) Without external flow control, directly connected.
(4) Without external flow control, indirectly connected.
These interceptors comply with the requirements of Table 1014.2.1. Hydromechanical grease interceptors are generally installed inside.
211.0 – I –
Indirect-Fired Water Heater. A water heater consisting of a storage tank equipped with an internal or external heat exchanger used to transfer heat from an external source to heat potable water. The storage tank either contains heated potable water or water supplied from an external source, such as a boiler.
Indirect Waste Pipe. A pipe that does not connect directly to the drainage system but conveys liquid wastes by discharging into a plumbing fixture, interceptor, or receptacle that is directly connected to the drainage system.
Individual Vent. A pipe installed to vent a fixture trap, and that connects with the vent system above the fixture served or terminates in the open air.
Industrial Waste. Liquid or water-borne waste from industrial or commercial processes, except domestic sewage.
Insanitary. A condition that is contrary to sanitary principles or is injurious to health.
Conditions to which “insanitary” shall apply include the following:
(1) A trap that does not maintain a proper trap seal.
(2) An opening in a drainage system, except where lawful that is not provided with an approved liquid-sealed trap.
(3) A plumbing fixture or other waste discharging receptor or device that is not supplied with water sufficient to flush and maintain the fixture or receptor in a clean condition.
(4) A defective fixture, trap, pipe, or fitting.
(5) A trap, except where in this code exempted, directly connected to a drainage system, the seal of which is not protected against siphonage and backpressure by a vent pipe.
(6) A connection, cross-connection, construction, or condition, temporary or permanent that would permit or make possible by any means whatsoever for an unapproved foreign matter to enter a water distribution system used for domestic purposes.
(7) The preceding enumeration of conditions to which the term “insanitary” shall apply, shall not preclude the application of that term to conditions that are, in fact, insanitary.
2025 CALIFORNIA PLUMBING CODE 37
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DEFINITIONS
that maintains a periodic inspection program of production of labeled products, installations, equipment, or materials and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.
Lavatories in Sets. Two or three lavatories that are served by one trap. Lavatory. [HCD 1 & HCD 2] “Lavatory” shall mean a plumbing fixture used for washing the hands, arms, face and head.
Leader. An exterior vertical drainage pipe for conveying storm water from roof or gutter drains. See Downspout. _**Limited-Density Owner-Built Rural Dwelling.
CPC § 0.9 Medium relevance — show source text
003)|Tension-controlled_3_|0.9|(e)|0.9|(f)| |1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
2. ε_t_
* is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
2. ε_t_
* is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
2. ε_t_
* is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
2. ε_t_
* is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
2. ε_t_
* is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
2. ε_t_
* is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1909A.1.12 ACI 318, Section 24.2.1. Add Section 24.2.1.1 to ACI 318 as follows:
CPC § 17.44 Medium relevance — show source text
85| |60|30|7:12|17.44|18.99|22.29|25.85|29.67|33.76|12.54| |60|30|12:12|24.62|26.81|31.46|36.49|41.89|47.66|14.48| |60|45|< 1:12|10.27|11.18|13.12|15.21|17.47|19.87|10.50| |60|45|5:12|14.26|15.52|18.22|21.13|24.26|27.60|12.82| |60|45|7:12|20.21|22.01|25.83|29.95|34.39|39.12|13.86| |60|45|12:12|31.20|33.97|39.87|46.23|53.07|60.39|16.76| |60|60|< 1:12|10.64|11.59|13.60|15.77|18.11|20.60|10.70| |60|60|5:12|14.77|16.09|18.88|21.90|25.14|28.60|13.79| |60|60|7:12|23.05|25.09|29.45|34.15|39.21|44.61|15.18| |60|60|12:12|37.97|41.34|48.52|56.27|64.60|73.49|19.05| |For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 pound force per linear foot = 0.146 kN/m, 1 pound per square foot = 47.88 Pa.
a. Tabulated lengths were derived by calculating design wind pressures in accordance with Figure 28.4-1 of ASCE 7 for a building with a mean roof height of 35 feet, topographic
factor,Kzt, equal to 1.0, and Risk Category II. For wind perpendicular to the ridge, the effects of a 2-foot overhang on each endwall are included. The design pressures were
used to calculate forces to be resisted by solid wall segments in each endwall. The forces to be resisted by each wall line were then divided by the default design strength of
840 pounds per linear foot of length to determine the unreduced length,UR, of solid wall length required in each endwall. The actual mean roof height of the building shall
not exceed the least horizontal dimension of the building.
b. Tabulated lengths in the “minimum” column are based on the requirement of Section 28.4.4 of ASCE 7 that the main windforce-resisting system be designed for a minimum
pressure of 1016 psf multiplied by the wall area of the building and 8 psf multiplied by the roof area of the building projected onto a vertical plane normal to the assumed
wind direction. Tabulated lengths in shaded cells are less than the “minimum” value. Where the minimum controls, it is permitted to be reduced in accordance with Notes c,
d and e. See Section R608.7.1.1.
c.
Frequently asked questions
What is the difference between a leader and a downspout?
A Leader is the exterior vertical pipe conveying stormwater; Downspout is the rain leader specifically from the roof to the building storm drain or other disposal point outside the building. These terms are defined in the CPC definitions.
Do leaders always need traps?
No — traps are required where leaders connect to a combined sewer; they are not required where the sewer carries storm water only. See § 1101.15 and § 1101.15.1.
Where must I put a cleanout for a leader?
A cleanout is required at the base of any rain leader or conductor before it connects to the horizontal building storm drain. § 1101.13.1.
Can I use a soil stack as a leader if it’s convenient?
No. Leaders/conductors cannot be used as soil, waste, or vent pipes — they are separate systems. § 1101.16.
How do I size a downspout for my roof?
Size vertical leaders/downspouts by the projected roof area they serve using Table 1103.1 and the applicable rainfall rate per § 1103.1. If you want, provide the roof area and local rainfall intensity and I can walk through the table selection.
More in California Plumbing Code
- Administration
- Definitions
- General Regulations
- Plumbing Fixtures and Fixture Fittings
- Water Heaters
- Water Supply and Distribution
- Sanitary Drainage (Drain, Waste, and Vent)
- Indirect Wastes
- Vents
- Traps and Interceptors
- Storm Drainage
- Fuel Gas Piping
- Health Care Facilities — Medical Gas and Medical Vacuum Systems
- Alternate Water Sources and Nonpotable Rainwater Catchment Systems
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