CPC · California Plumbing Code
When are scuppers required and how must they be sized and located?
If your roof has a parapet or raised edge that can trap water, the California Plumbing Code requires scuppers (or a secondary drain system). Scuppers must be at least 4 inches high, have a width equal to the circumference of the required roof drain (sized per Table 1103.1), and — for controlled‑flow roofs — the scupper bottom must be no higher than the maximums in Table 1105.1(2). Use Appendix D (Table D104.1) for rectangular‑scupper capacity guidance and always confirm Appendix acceptance with the Authority Having Jurisdiction.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Scuppers are required where the roof perimeter construction extends above the roof such that water will be entrapped (i.e., the roof can pond) — see § 1101.12.2.1. When used for secondary (emergency) drainage, scuppers must be sized so ponding does not exceed the depth the roof was designed for and scupper openings must be at least 4 inches high and have a width equal to the circumference of the roof drain required for the area served (sized per Table 1103.1) § 1101.12.2.1 . Where controlled‑flow storage is used, scuppers in parapet walls must not have their bottoms higher than the limits shown in Table 1105.1(2) .
The single most important rule: when the roof edge (parapet or raised curb) will trap water, you must provide scuppers or an alternate secondary drain sized and located so the water never ponds deeper than the roof was designed to support (§ 1101.12.2.1).
Requirements in detail
When scuppers are required
- Scuppers (or an open‑sided roof) are required where the roof perimeter extends above the roof plane in a way that will entrap water and cause ponding — § 1101.12.2.1.
- Alternative to scuppers: a secondary roof drain arrangement is permitted (see § 1101.12.2.2), but scuppers are the specified method when using open‑sided roof or parapet solutions.
Minimum shape/size/height of scupper openings
- Minimum opening height: 4 inches (102 mm). Width must equal the circumference of the roof drain required for the area served, sized in accordance with Table 1103.1 — § 1101.12.2.1.
- Additional installation details (flashing and cants): flashings must extend above the top of the scuppers and 45° cants are required at a wall or parapet — these requirements are stated in the storm drainage provisions.
Vertical location (how high above the roof)
- For roofs using controlled‑flow storage, scupper bottom elevation above the roof must not exceed the values in Table 1105.1(2). The table ties allowable scupper bottom heights to the roof rise (slope) because the maximum allowable ponding depth varies with roof slope — Table 1105.1(2).
Decision‑relevant dimensions (quick reference)
| Requirement / value | Decision use | Code Reference |
|---|---|---|
| Scupper minimum opening height: 4 in (102 mm) | Minimum vertical opening for any scupper | § 1101.12.2.1 |
| Scupper width = circumference of required roof drain (per Table 1103.1) | Horizontal opening width sizing rule | § 1101.12.2.1 |
| Maximum distance of scupper bottom above roof (flat): 3 in | Controlled‑flow limit for flat roofs | Table 1105.1(2) |
| Maximum distance of scupper bottom above roof (2" rise): 4 in | Controlled‑flow limit for 2" rise | Table 1105.1(2) |
| Maximum distance of scupper bottom above roof (4" rise): 5 in | Controlled‑flow limit for 4" rise | Table 1105.1(2) |
| Maximum distance of scupper bottom above roof (6" rise): 6 in | Controlled‑flow limit for 6" rise | Table 1105.1(2) |
| Appendix D guidance — rectangular scupper capacity table | Use Table D104.1 to select scupper width vs head when checking capacity (guidance table) | Table D104.1 (Appendix D) |
Notes on capacity and head:
- The CPC Appendix D contains a capacity table for rectangular scuppers (Table D104.1) giving discharge (gpm) for various widths and heads; it also states the head is measured above the bottom of the scupper and recommends the scupper height be not less than two times the design head (Appendix guidance) — see Table D104.1 and notes. Appendix D is guidance/engineering support; consult the Authority Having Jurisdiction about mandatory adoption of Appendix provisions.
How sizing ties to roof‑drain sizing tables
- The scupper width must equal the circumference of the roof drain required for the area — that roof‑drain requirement is determined using Table 1103.1 (sizing by roof area or flow). In practice you determine the roof drain size per Table 1103.1, calculate its circumference, and provide scupper(s) whose width equals that circumference (or use Appendix D capacity guidance to size rectangular scuppers) — § 1101.12.2.1.
Exceptions & special cases
- Controlled‑flow roofs (storage on roof) have explicit maximum ponding depths and parapet scupper height limits in Table 1105.1(1) and Table 1105.1(2); scuppers in parapet walls must meet the heights in Table 1105.1(2) when controlled‑flow is used. The controlled‑flow method itself has conditions (storage limits, number of drains, prefabricated weirs, etc.) — see § 1105.0 and associated tables.
- Setback roofs: drains on setback roofs may be connected to a controlled‑flow system only under the conditions in § 1105.2 (for example, if the setback is designed for storing water, or the area is converted to gpm and pipe sizes adjusted) — check § 1105.2 before assuming scuppers suffice.
- Appendix D (including Table D104.1) is prescriptive guidance for scupper hydraulic capacity but is part of the Appendix; verify with the AHJ whether Appendix methods are required for your project.
Common mistakes
- Assuming any hole in a parapet counts as a scupper — scuppers must meet the minimum 4 in height and width rules tied to required roof drain circumference (not arbitrary openings) — § 1101.12.2.1.
- Placing the scupper bottom higher than permitted for controlled‑flow roofs — always check Table 1105.1(2) when the controlled‑flow approach or parapet storage is used.
- Using Appendix D discharge numbers as mandatory without confirming AHJ adoption — Appendix D provides useful capacity tables (Table D104.1) but is guidance unless adopted. Always confirm whether Appendix methods are acceptable.
- Forgetting flashing detail and cants — the code requires flashings to extend above the top of scuppers and 45° cants at walls/parapets; omitting these leads to water intrusion/roof damage.
Worked example — concrete scenario applying the rule
Scenario: flat commercial roof (parapet that will trap water), design requires secondary scuppers. The design maximum ponding depth allowable (from the registered design professional) is 3 inches. The hydraulic design indicates the scupper(s) must evacuate ≈300 gpm during the emergency condition.
Minimum vertical height: code requires scupper opening height ≥ 4 in (102 mm) — § 1101.12.2.1. If Appendix D guidance is used and it recommends scupper height ≥ 2×design head, for a 3 in head that would be 6 in tall; confirm with AHJ whether Appendix D rule is required.
Capacity check with Appendix D (guidance): Table D104.1 (Appendix D) shows for a head = 3 in the rectangular scupper discharge:
- 12 in wide → 177 gpm
- 18 in wide → 271 gpm
- 24 in wide → 364 gpm
To meet the required ~300 gpm at 3 in head you would select a 24 in wide rectangular scupper (because 18 in is ~271 gpm which is under 300 gpm, 24 in is 364 gpm which meets the requirement). Confirm the scupper height (≥4 in per § 1101.12.2.1; Appendix D recommends ≥6 in for a 3 in head) with the AHJ and structural engineer.
Vertical location: because this example is a flat roof, Table 1105.1(2) requires the scupper bottom be no more than 3 in above the roof level at the drain (for controlled‑flow situations). If using controlled‑flow storage, ensure scupper bottom meets that limit.
Width rule alternative: if the project uses standard circular roof drains sized per Table 1103.1, determine the required roof drain diameter and compute its circumference; the scupper width must equal that circumference per § 1101.12.2.1 (this is the mandatory code rule, whereas Appendix D gives rectangular weir capacities as guidance).
Always document the calculations and submit them with plans as required — the CPC requires drainage calculations be submitted to the AHJ.
Related provisions
- § 1101.12.2.1 — Roof scuppers / open‑sided roof (primary requirement)
- Table 1105.1(2) — Distance of scupper bottoms above roof (controlled‑flow limits)
- § 1105.2 — Setback roofs (conditions when setback drains connect to controlled‑flow systems)
- Appendix D, Table D104.1 — Discharge capacities for rectangular scuppers (guidance)
- § 1101.12.2.2 — Secondary roof drains (alternative to scuppers)
Code references
Grounded in the retrieved California Plumbing Code — click a citation to read the verbatim passage:
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
206 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
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 § 1103.1. High 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
208 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
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
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
CPC § 1103.1 High 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
208 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
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 § 1.11.0. Medium 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.
2025 CALIFORNIA PLUMBING CODE 395
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
396 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
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
CPC § 1502.2 Medium relevance — show source text
1||||X|X|||||||||||||||||||| |1502.2||||X|X|||||||||||||||||||| |1503.3 – 1503.4|||X|||||||||||||||||||||| |1505 – 1507|||X|||||||||||||||||||||| |1507.3.10||||||||X|X|X|X|X||X|X|||||||||| |1507.7.8||||||||X|X|X|X|X||X|X|||||||||| |1509 – 1511|||X|||||||||||||||||||||| |1511.9.6||||||X|X|||||||||||||||||| |1511.10– 1511.10.1|X|||X|X|||X|X|X|X|X||X|X|||||||||| |1512|||X|||||||||||||||||||||| |1513||||||||X|X|X|X|X||X|X||||||||||
The state agency does not adopt sections identified by 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.
2025 CALIFORNIA BUILDING CODE 15-1
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
15-2 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
15 ROOF ASSEMBLIES AND ROOFTOP STRUCTURES
User notes:
About this chapter: Chapter 15 provides minimum requirements for the design and construction of roof assemblies and rooftop structures. The criteria address the weather-protective barrier at the roof and, in most circumstances, a fire-resistant barrier. The chapter is largely prescriptive in nature and is based on decades of experience with various traditional materials, but it also recognizes newer products. Section 1511 addresses rooftop structures, which include penthouses, tanks, towers and spires. Rooftop penthouses larger than prescribed in this chapter must be treated as a story under Chapter 5.
ICC code development note: Code change proposals to sections preceded by the designation [BF] or [P] will be considered by one of the code development committees meeting during the 2024 (Group A) Code Development Cycle. All other code change proposals will be considered by a code development committee meeting during the 2025 (Group B) Code Development Cycle.
SECTION 1501—GENERAL
1501.1 Scope. The provisions of this chapter shall govern the design, materials, construction and quality of roof assemblies, and rooftop structures.
SECTION 1502—ROOF DRAINAGE
[P] 1502.1 General. Design and installation of roof drainage systems shall comply with this section, Section 1611 of this code and Chapter 11 of the California Plumbing Code .
[P] 1502.2 Secondary (emergency overflow) drains or scuppers. Where roof drains are required, secondary (emergency overflow) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason. The installation and sizing of secondary emergency overflow drains, leaders and conductors shall comply with Section 1611 of this code and Chapter 11 of the California Plumbing Code .
CPC § 1501.1 Medium relevance — show source text
ICC code development note: Code change proposals to sections preceded by the designation [BF] or [P] will be considered by one of the code development committees meeting during the 2024 (Group A) Code Development Cycle. All other code change proposals will be considered by a code development committee meeting during the 2025 (Group B) Code Development Cycle.
SECTION 1501—GENERAL
1501.1 Scope. The provisions of this chapter shall govern the design, materials, construction and quality of roof assemblies, and rooftop structures.
SECTION 1502—ROOF DRAINAGE
[P] 1502.1 General. Design and installation of roof drainage systems shall comply with this section, Section 1611 of this code and Chapter 11 of the California Plumbing Code .
[P] 1502.2 Secondary (emergency overflow) drains or scuppers. Where roof drains are required, secondary (emergency overflow) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason. The installation and sizing of secondary emergency overflow drains, leaders and conductors shall comply with Section 1611 of this code and Chapter 11 of the California Plumbing Code .
1502.3 Gutters. Gutters and leaders placed on the outside of buildings, other than Group R-3, private garages and buildings of Type V construction, shall be of noncombustible material or not less than Schedule 40 plastic pipe.
SECTION 1503—WEATHER PROTECTION
1503.1 General. Roof decks shall be covered with approved roof coverings secured to the building or structure in accordance with the provisions of this chapter. Roof coverings shall be designed in accordance with this code, and installed in accordance with this code and the manufacturer’s approved instructions.
1503.2 Flashing. Flashing shall be installed in such a manner so as to prevent water from entering the wall and roof through joints in copings, through moisture-permeable materials and at intersections with parapet walls and other penetrations through the roof plane.
1503.2.1 Locations. Flashing shall be installed at wall and roof intersections, at gutters, wherever there is a change in roof slope or direction and around roof openings. Where flashing is of metal, the metal shall be corrosion resistant with a thickness of not less than 0.019 inch (0.483 mm) (No. 26 galvanized sheet).
1503.3 Parapet walls. Parapet walls shall be coped or covered in accordance with Sections 1503.3.1 and 1503.3.2. The top surface of the parapet wall shall provide positive drainage.
1503.3.1 Fire-resistance-rated parapet walls. Parapet walls required by Section 705.12 shall be coped or covered with weatherproof materials of a width not less than the thickness of the parapet wall such that the fire-resistance rating of the wall is not decreased.
1503.3.2 Other parapet walls. Parapet walls meeting one of the exceptions in Section 705.12 shall be coped or covered with weatherproof materials of a width not less than the thickness of the parapet wall.
1503.4 Attic and rafter ventilation. Intake and exhaust vents for ventilation of attic and enclosed rafter assemblies shall be provided in accordance with Section 1202.2 and the vent product manufacturer’s installation instructions.
CPC § 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).
CPC § 103.0 Medium 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
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
CPC § 0.004 Medium relevance — show source text
35|0.004|–|–| |0.71|0.014|–|–| |1.06|0.029|–|–| |1.41|0.047|–|–| |1.77|0.070|–|–| |2.12|0.096|–|–| |2.47|0.125|–|–| |2.82|0.159|–|–| |3.18|0.195|–|–| |3.53|0.235|0.045|–| |4.24|0.324|0.062|–| |4.94|0.425|0.081|–| |5.65|0.539|0.103|–| |6.36|0.664|0.127|–| |7.06|0.802|0.153|0.038| |7.77|0.950|0.181|0.045| |8.47|1.110|0.211|0.053| |9.18|1.281|0.243|0.061| |9.89|1.463|0.278|0.070| |10.59|1.656|0.314|0.079| |12.36|2.186|0.413|0.103| |14.12|2.752|0.525|0.131| |15.89|3.442|0.648|0.162| |17.66|4.166|0.783|0.195| |19.42|–|0.929|0.231| |21.19|–|0.744|0.270| |22.95|–|0.858|0.312| |24.72|–|0.980|0.356| |28.25|–|1.244|0.453| |31.78|–|1.537|0.560| |35.31|–|1.858|0.677| |38.84|–|2.205|0.804| |42.37
|–
|2.581
|0.941
| |45.90
|–
|2.982
|1.088
| |49.43
|–
|3.411
|1.245
| |52.97
|–
|4.249
|1.411
| |56.50
|–
|–
|1.587
| |60.03
|–
|–
|1.772
| |63.56|–|–|1.967| |67.09|–|–|2.174| |70.62|–|–|2.385| |79.45|–|–|2.959| |88.28|–|–|3.589|For SI units: 1 standard cubic foot per minute = 28.32 SLPM, 1 inch = 25 mm, 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa
Notes: 1 Based on the pressure of 14.7 psig (101 kPa) at 68°F (20°C). 2 Based on the pressure of 55 psig (379 kPa) at 68°F (20°C).
CPC § 710.5 Medium relevance — show source text
Sizing . . . . . . . . . . . . .710.5, 717.0, Table 717.1, C 304.2 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .723.0 BUILDING SUPPLY . . . . . . . . . . . . . . . . . .204.0, Chapter 6 BURRED ENDS . . . . . . . . . . . . . . . . .309.3, 609.1, 701.3.1,
903.3, 1208.5.7, 1321.7.2
– C –
CAPACITY OF
Breathing air cylinders . . . . . . . . . . . . . . . . . . . .F 1001.1 Graywater systems . . . . . . . . . . . . . . . . . . . . . .1503.2.1 Interceptors . . . . . . . . . . . . . . . . . . . . . . . . . . . .1014.2.1 Irrigation field and
mulch basin . . . . . . . . . .1504.2, Table 1504.2, 1504.3
564 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
INDEX
Medical air compressors . . . . . . . . . . . .1310.3.1, 1311.2
Rectangular scuppers . . . . . . . . . . . . . . . . . . . .D 104.0
Sewage ejectors or pumps . . . . . . . . . . . . . . . . . .710.3
Sump pump . . . . . . . . . . . . . . . . . . . . . . . . . . . .1101.6.2
Water heaters . . . . . . . . . . . . . . . . . . .501.1, Table 501.1(1)
CAST-IRON PIPE
Approved standards . . . . . . . . . . . . . . . . . . . . . .301.2.4
Discharge line from ejectors . . . . . . . . . . . . . . . . .710.4
Drainage piping . . . . . . . . . . . . . . . . . . . . . . . . . . .701.2
Fittings . . . . . . . . . . . . . . . . . .301.2.3, 604.6, 1208.5.9.5
Flanges . . . . . . . . . . . . . . . . . . . . . . . . . . . .1208.5.11.1
Joining . . . . . . . . . . . . . . . . . . . . . . . . . .705.2, 705.10.1
Prohibited use . . . . . . . . . . . . . . . . . . . .316.1, 1208.5.2
CPC § 2.1 Medium relevance — show source text
R903.2.1 Locations. Flashings shall be installed at wall and roof intersections, wherever there is a change in roof slope or direction and around roof openings. A flashing shall be installed to divert the water away from where the eave of a sloped roof intersects a vertical sidewall. Where flashing is of metal, the metal shall be corrosion resistant with a thickness of not less than 0.019 inch (0.5 mm) (No. 26 galvanized sheet).
R903.2.2 Crickets and saddles. A cricket or saddle shall be installed on the ridge side of any chimney or penetration more than 30 inches (762 mm) wide as measured perpendicular to the slope. Cricket or saddle coverings shall be sheet metal or of the same material as the roof covering.
Exception: Unit skylights installed in accordance with Section R324.6 and flashed in accordance with the manufacturer’s instructions shall be permitted to be installed without a cricket or saddle.
R903.3 Coping. Parapet walls shall be properly coped with noncombustible, weatherproof materials of a width not less than the thickness of the parapet wall.
R903.4 Roof drainage. Unless roofs are sloped to drain over roof edges, roof drains shall be installed at each low point of the roof.
R903.4.1 Secondary (emergency overflow) drains or scuppers. Where roof drains are required, secondary emergency overflow roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason. Overflow drains having the same size as the roof drains shall be installed with the inlet flow line located 2 inches (51 mm) above the low point of the roof, or overflow scuppers having three times the size of the roof drains and having a minimum opening height of 4 inches (102 mm) shall be installed in the adjacent parapet walls with the inlet flow located 2 inches (51 mm) above the low point of the roof served. The installation and sizing of overflow drains, leaders and conductors shall comply with the California Plumbing Code .
SECTION R904—MATERIALS
R904.1 Scope. The requirements set forth in this section shall apply to the application of roof covering materials specified herein. Roof assemblies shall be applied in accordance with this chapter and the manufacturer’s installation instructions. Installation of roof assemblies shall comply with the applicable provisions of Section R905.
R904.2 Compatibility of materials. Roof assemblies shall be of materials that are compatible with each other and with the building or structure to which the materials are applied.
R904.3 Material specifications and physical characteristics. Roof covering materials shall conform to the applicable standards listed in this chapter.
R904.4 Product identification. Roof covering materials shall be delivered in packages bearing the manufacturer’s identifying marks and approved testing agency labels required. Bulk shipments of materials shall be accompanied by the same information issued in the form of a certificate or on a bill of lading by the manufacturer.
SECTION R905—REQUIREMENTS FOR ROOF COVERINGS
R905.1 Roof covering application. Roof coverings shall be applied in accordance with the applicable provisions of this section and the manufacturer’s installation instructions. Unless otherwise specified in this section, roof coverings shall be installed to resist the component and cladding loads specified in Table R301.2.1(1), adjusted for height and exposure in accordance with Table R301.2.1(2).
CPC § 104.1 Medium relevance — show source text
402 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
APPENDIX D
Col1 TABLE D 104.1 DISCHARGE FROM RECTANGULAR SCUPPERS (gallons per minute)1, 2, 3, 4 Col3 Col4 Col5 Col6 Col7 WATER HEAD
(inches)WIDTH OF SCUPPER (inches) WIDTH OF SCUPPER (inches) WIDTH OF SCUPPER (inches) WIDTH OF SCUPPER (inches) WIDTH OF SCUPPER (inches) WIDTH OF SCUPPER (inches) WATER HEAD
(inches)6 12 18 24 30 36 1⁄2 6 13 19 25 32 38 1 17 35 53 71 89 107 11⁄2 31 64 97 130 163 196 2 – 98 149 200 251 302 21⁄2 – 136 207 278 349 420 3 – 177 271 364 458 551 31⁄2 – – 339 457 575 693 4 – – 412 556 700 844 For SI units: 1 inch = 25.4 mm, 1 gallon per minute = 0.06 L/s
Notes: 1 Table D 104.1 is based on discharge over a rectangular weir with end contractions. 2 The head is the depth of water above the bottom of the scupper opening. 3 The height of the scupper opening shall be not less than two times the design head. 4 Coordinate the allowable head of water with the structural design of the roof.
2025 CALIFORNIA PLUMBING CODE 403
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
404 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE
APPENDIX E - MANUFACTURED/MOBILE HOME PARKS AND RECREATIONAL VEHICLE PARKS
(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
Frequently asked questions
When exactly must I use a scupper instead of a secondary roof drain?
Use a scupper (or open‑sided edge) when the roof perimeter extends above the roof and will entrap water. A secondary roof drain system is an alternate method; the code lists both options — see § 1101.12.2.1 and § 1101.12.2.2.
How tall must a scupper opening be?
Scupper openings must be at least 4 inches (102 mm) high per § 1101.12.2.1. Appendix D guidance may require the scupper height to be at least 2× the design head; confirm AHJ adoption.
How do I pick a scupper width?
The code mandates the scupper width equal the circumference of the roof drain required for the area served (determine roof drain size per Table 1103.1) — § 1101.12.2.1. Alternatively, Appendix D Table D104.1 gives rectangular‑weir capacities for selecting width by required gpm and head.
How high above the roof can the scupper bottom be?
When using controlled‑flow (storage) methods, scupper bottoms must not be higher than the values in Table 1105.1(2) (for example, 3 in for flat roofs) — Table 1105.1(2).
Is Appendix D required for scupper sizing?
Appendix D provides hydraulic tables (e.g., Table D104.1) that are guidance/engineering support. Appendix material is not mandatory unless specifically adopted by the AHJ; confirm whether Appendix methods are required or accepted for your project.
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
Ask about the CPC
Get cited, plain-English answers on the California Plumbing Code for your project — any code section, any scenario.
Start Free Trial