CRC · California Residential Code
Storm drainage materials & roof/roof‑leader sizing
A homeowner must use approved materials for subsoil and roof drains, install perimeter subsoil drains of at least 3" diameter set in at least 4" of porous aggregate, and if stormwater cannot drain by gravity provide an accessible sump with an automatic pump; roof drains, gutters and downspouts are sized using local rainfall rates (Table D101.1) and the code sizing tables (Table 1103.1) and secondary/emergency drains (scuppers or secondary drains) must meet the code dimensions and locations (see **§ 1101.4** and **§ 1101.6.2**) .
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
The California storm‑drain rules require that materials for storm and subsoil drains be approved materials and that subsoil drains be sized, installed and discharged per the plumbing code; see § 1101.4 for permitted materials and § 1101.6.2 for sump requirement where gravity discharge is not possible. Roof drainage (primary and secondary) and sizing of gutters, leaders and drains are sized using the rainfall rates and sizing tables referenced in the code (Table D101.1 and Table 1103.1) and primary systems are sized for a 60‑minute, 100‑year storm unless the AHJ requires otherwise (see § 1101.12 and § 1103.1) .
The essential rule: use only approved materials for storm and subsoil drains, install subsoil drains at no less than 3 inches diameter with proper surround, and if gravity discharge isn’t possible provide an accessible sump with an automatic pump (see § 1101.4 and § 1101.6.2) .
Requirements in detail
Key defined terms (first use bolded)
- Subsoil drain — open‑jointed or perforated drain tile/pipe used around foundations; materials listed in § 1101.4 and Table 1101.4.6.
- Leader (rain leader/vertical conductor) — vertical downspout piping; sizing by projected roof area using Table 1103.1.
- Sump — accessible sump with approved automatic pump used when gravity discharge is not possible (see § 1101.6.2).
- Primary drainage / Secondary (emergency) drainage — primary sized for the design storm; secondary must be provided by scuppers, secondary drains or other methods specified in § 1101.12.
Materials: what the code permits
- Materials for subsoil drains are required to conform to the referenced standards and are listed in Table 1101.4.6 under § 1101.4 (examples: PE per ASTM F667, PVC per ASTM D2729, vitrified clay per ASTM C4/C700).
- Roof drains themselves must be constructed of approved metals or plastics and comply with ASME standards (see § 1102.1).
- Leaders installed outside must meet the applicable aboveground pipe or sheet‑metal standards (see § 1101.4.3).
Sizing rules — how to size gutters, leaders and drains
- Primary roof drainage and vertical/horizontal storm drains are sized using the local rainfall intensity for a 60‑minute duration, 100‑year return period (see § 1101.12), using Table D101.1 to obtain inches/hour or gpm/sf and then applying Table 1103.1 / Table 1103.2 to get pipe/gutter sizes or allowable roof area per inlet.
- Secondary (emergency) drainage must be provided (scuppers or secondary drains) and secondary drains are located not less than 2 inches above the roof surface (see § 1101.12.2.2) .
- Scupper openings must be not less than 4 inches high; width shall equal the circumference of the roof drain required for the area served (see § 1101.12.2.1) .
Compact decision table (decision‑relevant dimensions/values)
| Parameter / decision input | Requirement / value to use | When/why | Code Reference |
|---|---|---|---|
| Allowed subsoil drain materials | PE (ASTM F667), PVC (ASTM D2729), vitrified clay (ASTM C4/C700), etc. | Use approved material per table | § 1101.4 / Table 1101.4.6 |
| Minimum subsoil drain diameter | 3 inches (80 mm) | Perimeter subsoil drains around basements/crawlspaces | § 1101.6 |
| Surrounding filter/aggregate | Not less than 4 inches (102 mm) of gravel/approved porous material around pipe; provide exterior filter media | To prevent clogging and ensure free drainage | § 1101.6 |
| Sump required when gravity not possible | Provide accessible sump with approved automatic electric pump | Where gravity discharge cannot be provided | § 1101.6.2 |
| Primary roof drainage storm design | 60‑minute duration, 100‑year return period (unless AHJ requires otherwise) | Basis for sizing gutters, leaders, drains | § 1101.12.1 |
| Secondary roof drain minimum elevation | Not less than 2 inches (51 mm) above roof | Location of secondary roof drains | § 1101.12.2.2 |
| Scupper minimum opening height | 4 inches (102 mm) | Secondary scupper sizing | § 1101.12.2.1 |
| Leader/vertical conductor sizing | Use projected roof area → Table 1103.1 | Size vertical conductors by max projected roof area | § 1103.1 / Table 1103.1 |
| Use of local rainfall rates | Use Table D101.1 (gpm/sf or in/hr) for local city | To convert roof area to required flow (gpm) | Appendix D / Table D101.1 |
Installation & ancillary requirements
- Leaders must not be used as soil, waste or vent pipes and vice versa (prohibition on mixing functions) — § 1101.16.
- Cleanouts: Rain leaders and conductors connected to a building storm sewer require a cleanout at the base before the horizontal drain — § 1101.13.1.
- Roof drains require dome strainers and watertight flashings; where lead/copper flashing is used minimum weights are specified (see § 1102.2 and § 1102.3).
Exceptions & special cases
- Where subsoil drains are not required: HCD jurisdictions may make subsoil drains mandatory only when required by the Authority Having Jurisdiction due to geological conditions (exception in § 1101.6) — check local AHJ. .
- Secondary drain systems may be installed as a separate piping system that discharges above grade observable by occupants (sized per primary design rainfall) or combined into the primary vertical piping but then sized for double the rainfall rate for the local area (see § 1101.12.2.2.1 and § 1101.12.2.2.2) .
- Controlled‑flow and engineered systems: If using storage/controlled flow on roofs or siphonic systems, alternate sizing and design standards apply (see § 1105.0 and § 1106.2) — these are engineered approaches with additional requirements. .
Common mistakes
- Using sanitary sewer outlets for storm water (storm → sanitary is prohibited by § 1101.3) — do not connect storm discharge to sanitary sewers unless a combined sewer exists and you meet the combined‑sewer rules. .
- Failing to size leaders/gutters from the correct local rainfall intensity (forgetting to consult Table D101.1 and Table 1103.1). The code requires using those tables unless the AHJ specifies otherwise. .
- Installing subsoil drain piping smaller than 3 inches or without the required aggregate/filter wrap (violates § 1101.6) — leads to clogging and noncompliance. .
- Not providing an accessible sump and automatic pump where gravity discharge cannot be achieved (required by § 1101.6.2). .
- Using non‑listed materials or ignoring agency‑specific limitations (e.g., OSHPD restrictions on ABS/PVC in certain facilities) — confirm the applicable adoption table for your agency. .
Worked example — roof leader sizing (code method shown in the text)
The code provides a worked approach in Appendix D to convert allowable roof area to a rainfall rate. The commentary example in D103.1 shows:
- Given: a 6‑inch leader/drain at 1/8 inch per foot slope has an allowable roof area of 21,400 ft² per 1 inch/hour. For a local rainfall intensity of 3.2 in/hr, allowable roof area = 21,400 / 3.2 = 6,688 ft². That is, a 6‑inch downspout can serve up to 6,688 ft² at 3.2 in/hr using the table method (example in D103.1). Use Table 1103.1 to find the base area per 1 in/hr for the selected pipe size and then divide by the actual local in/hr to get allowable area at your location. .
Step‑by‑step (how you would apply it to your project):
- Look up your city in Table D101.1 to obtain the design rainfall intensity (in/hr or gpm/sf) for the 60‑minute, 100‑year event. .
- From Table 1103.1, note the allowable square feet of roof area per 1 in/hr for candidate leader/gutter sizes (the table lists allowable areas at various slopes). .
- Divide the table value (ft² per 1 in/hr) by your local in/hr to obtain the allowable ft² for that leader size at your locality (as in the D103.1 example). .
- Choose the smallest leader/gutter size whose allowable area ≥ your actual projected roof area. Ensure secondary/emergency drainage is provided per § 1101.12 and scuppers/secondary drains meet required dimensions. .
Related provisions
- § 1101.3 — Storm water drainage to sanitary sewer prohibited.
- § 1101.4 — Material uses and Table 1101.4.6 (materials for subsoil drainpipe).
- § 1101.6 / § 1101.6.2 — Subsoil drains and sump requirement.
- § 1101.12 — Roof drainage (primary and secondary roof drainage).
- § 1102.1 — Roof drain permitted materials and standards (ASME references).
- § 1103.1 and Table 1103.1 — Size of vertical conductors/leaders (by projected roof area).
- Appendix D (Table D101.1) — Local rainfall intensities for sizing (60‑minute, 100‑year).
- § 1101.13.1 — Cleanouts at base of leaders.
- § 1101.15 — Traps on storm drains and leaders when connected to combined sewer.
- § 1105.0 — Controlled‑flow roof drainage rules (alternate method).
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 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.
CRC § 1.11.0. High relevance — show source text
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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APPENDIX D
SIZING STORM WATER DRAINAGE SYSTEMS
The provisions contained in this appendix are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance.
D 101.0 General.
D 101.1 Applicability. This appendix provides general guidelines for the sizing of storm water drainage systems based on maximum rates of rainfall for various cities. The rainfall rates in Table D 101.1 shall be permitted to be used for design unless higher values are established locally.
D 102.0 Sizing by Flow Rate. D 102.1 General. Storm drainage systems shall be permitted to be sized by storm water flow rates, using the gallons per minute per square foot [(L/s)/m [2] ] of rainfall listed in Table D 101.1 for the local area. Multiplying the listed gallons per minute per square foot [(L/s)/m [2] ] by the roof area being drained (in square feet) (m [2] ) by each inlet produces the gallons per minute (gpm) (L/s) of required flow for sizing each drain inlet. The flow rates shall be permitted to be added to determine the flows in each of the drainage systems. Required pipe sizes for various flow rates are listed in Table 1103.1 and Table 1103.2.
D 103.0 Sizing by Roof Area. D 103.1 General. Storm drainage systems shall be permitted to be sized using the roof area served by each of the
drainage systems. Maximum allowable roof areas with various rainfall rates are listed in Table 1103.1 and Table 1103.2, along with the required pipe sizes. By using this method, it shall be permitted to interpolate between two listed rainfall rate columns (inches per hour) (mm/h). To determine the allowable roof area for a listed pipe size at a listed slope, divide the allowable square feet (m [2] ) of the roof for a 1 inch per hour (in/h) (25.4 mm/h) rainfall rate by the listed rainfall rate for the local area. For example, the allowable roof area for a 6 inch (150 mm) drain at [1] ⁄ 8 inch per foot (10.4 mm/m) slope with a rainfall rate of 3.2 in/h (81 mm/h) is 21 400/3.2 = 6688 square feet (621.3 m [2] ).
D 104.0 Capacity of Rectangular Scuppers. D 104.1 General. Table D 104.1 lists the discharge capacity of rectangular roof scuppers of various widths with various heads of water. The maximum allowable level of water on the roof shall be obtained from the registered design professional, based on the design of the roof.
TABLE D 101.1
CRC § 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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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 CRC § 103.0 High relevance — show source text
D 103.0 Sizing by Roof Area. D 103.1 General. Storm drainage systems shall be permitted to be sized using the roof area served by each of the
drainage systems. Maximum allowable roof areas with various rainfall rates are listed in Table 1103.1 and Table 1103.2, along with the required pipe sizes. By using this method, it shall be permitted to interpolate between two listed rainfall rate columns (inches per hour) (mm/h). To determine the allowable roof area for a listed pipe size at a listed slope, divide the allowable square feet (m [2] ) of the roof for a 1 inch per hour (in/h) (25.4 mm/h) rainfall rate by the listed rainfall rate for the local area. For example, the allowable roof area for a 6 inch (150 mm) drain at [1] ⁄ 8 inch per foot (10.4 mm/m) slope with a rainfall rate of 3.2 in/h (81 mm/h) is 21 400/3.2 = 6688 square feet (621.3 m [2] ).
D 104.0 Capacity of Rectangular Scuppers. D 104.1 General. Table D 104.1 lists the discharge capacity of rectangular roof scuppers of various widths with various heads of water. The maximum allowable level of water on the roof shall be obtained from the registered design professional, based on the design of the roof.
TABLE D 101.1
MAXIMUM RATES OF RAINFALL FOR VARIOUS CITIES*
STATES AND CITIES STORM DRAINAGE 60-MINUTE DURATION, 100-YEAR RETURN Col3 STATES AND CITIES inches per hour gallons per minute per square foot ALABAMA – – Birmingham 3.7 0.038 Huntsville 3.3 0.034 Mobile 4.5 0.047 Montgomery 3.8 0.039 ALASKA – – Aleutian Islands 1.0 0.010 Anchorage 0.6 0.006 Bethel 0.8 0.008 Fairbanks 1.0 0.010 Juneau 0.6 0.006 ARIZONA – – Flagstaff 2.3 0.024 Phoenix 2.2 0.023 Tucson 3.0 0.031 ARKANSAS – – Eudora 3.8 0.039 Ft. Smith 3.9 0.041 Jonesboro 3.5 0.036 Little Rock 3.7 0.0382025 CALIFORNIA PLUMBING CODE 397
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CRC § 1103.4 Medium relevance — show source text
area.
(5) Two opposite walls of differing heights – add 50 percent of the wall area above the top of the lower wall. (6) Walls on three sides – add 50 percent of the area of the inner wall below the top of the lowest wall, plus an allowance for the area of the wall above the top of the lowest wall, in accordance with Section 1103.4(3) and Section 1103.4(5) above. (7) Walls on four sides – no allowance for wall areas below the top of the lowest wall – add for areas above the top of the lowest wall in accordance with Section 1103.4(1), Section 1103.4(3), Section 1103.4(5), and Section 1103.4(6) above.
1104.0 Values for Continuous Flow.
1104.1 General. Where there is a continuous or semi-continuous discharge into the building storm drain or building storm sewer, as from a pump, ejector, air-conditioning plant, or similar device, 1 gpm (0.06 L/s) of such discharge shall be computed as being equivalent to 24 square feet (2.2 m [2] ) of roof area, based upon a rate of rainfall of 4 inches per hour (in/h) (102 mm/h).
1105.0 Controlled-Flow Roof Drainage. 1105.1 Application. Instead of sizing the storm drainage system in accordance with Section 1103.0, the roof drainage shall be permitted to be sized by controlled flow and storage of the storm water on the roof, provided the following conditions are met:
(1) The water from a 25-year frequency storm shall not be stored on the roof exceeding 24 hours. (2) During the storm, the water depth on the roof shall not exceed the depths specified in Table 1105.1(1). (3) Not less than two drains shall be installed in roof areas of 10 000 square feet (929 m [2] ) or less, and not less than one additional drain shall be installed for each 10 000 square feet (929 m [2] ) of roof area exceeding 10 000 square feet (929 m [2] ). (4) Each roof drain shall have a precalibrated, fixed (nonadjustable), and proportional weir (notched) in a standing water collar inside the strainer. No mechanical devices or valves shall be permitted. (5) Pipe sizing shall be based on the pre-calibrated rate of flow (gpm) (L/s) of the pre-calibrated weir for the maximum allowable water depth, and Table 1103.1 and Table 1103.2.
(6) The height of stones or other granular material above the waterproofed surface shall not be considered in water depth measurement, and the roof surface in the vicinity of the drain shall not be recessed to create a reservoir.
(7) Roof design, where controlled-flow roof drainage is used, shall be such that the design roof live load is not less than 30 lb/ft [2] (146 kg/m [2] ) to provide a safety factor exceeding the 15 lb/ft [2] (73 kg/m [2] ) represented by the depth of water stored on the roof in accordance with Table 1105.1(1). (8) Scuppers shall be provided in parapet walls. The distance of scupper bottoms above the roof level at the drains shall not exceed the maximum distances specified in Table 1105.1(2).
CRC § 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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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
CRC § 408.8.3 Medium 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
CRC § 1103.1. Medium relevance — show source text
(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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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
ROOF RISE*
(inches)ABOVE ROOF LEVEL
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.
1105.2 Setback Roofs. Drains on setback roofs shall be permitted to be connected to the controlled-flow drainage systems provided:
(1) The setback is designed for storing water, or
(2) The square footage of the setback drainage area is converted as outlined in Section 1105.0 to gpm, and the storm-water pipe sizes in the controlled-flow system are based on the sum of the loads.
(3) The branch from each of the roof drains that are not provided with controlled flow shall be sized in accordance
with Table 1103.1.
1106.0 Engineered Storm Drainage System. 1106.1 General. The design and sizing of a storm drainage system shall be permitted to be determined by accepted engineering practices. The system shall be designed by a regis
TABLE 1105.1(1) CONTROLLED-FLOW MAXIMUM ROOF WATER DEPTH
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
For SI units: 1 inch = 25.4 mm
CRC § 1101.7 Medium 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.
CRC § 1101.12.2.2 Medium 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
206 2025 CALIFORNIA PLUMBING CODE
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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.
CRC § 1101.16 Medium 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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), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
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
CRC § 1101.16 Medium 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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Frequently asked questions
Do subsoil drains always have to be installed around a house?
Not always. The code requires subsoil drains around buildings with basements, cellars, crawl spaces or floors below grade, but in some HCD jurisdictions subsoil drains are mandatory only where the Authority Having Jurisdiction requires them due to geological conditions (see § 1101.6) .
What if I cannot get gravity discharge for my subsoil drain?
If gravity discharge is not possible, you must provide an accessible sump equipped with an approved automatic electric pump to lift and discharge the subsoil drain water (see § 1101.6.2) .
How do I know what rainfall intensity to use for sizing?
Use the local rainfall intensity for a 60‑minute, 100‑year storm from Table D101.1 (Appendix D) unless the AHJ directs otherwise; convert that to gpm/sf or use Table 1103.1 per the code method. .
Are there limits on materials for roof drains and leaders?
Yes. Roof drains must be constructed of listed metals or plastics and comply with ASME standards (see § 1102.1). Subsoil and underground storm piping must use materials listed in Table 1101.4.6 under § 1101.4. Also check any agency‑specific restrictions (e.g., OSHPD). .
Do I need a cleanout for an exterior leader?
Yes — rain leaders and conductors that connect to a building storm sewer require a cleanout at the base before they connect to the horizontal drain (see § 1101.13.1) .
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