CPC · California Plumbing Code
What are the rules for controlled‑flow roof drainage (precalibrated weirs, ponding depths)?
Controlled‑flow roof drainage lets a roof hold and meter stormwater instead of sizing for full runoff, but the CPC requires that 25‑year storm water be released within 24 hours, ponding depths be limited to values in Table 1105.1(1) (e.g., 3" for flat roofs), each drain use a precalibrated fixed notched weir (no valves), a minimum number of drains be installed based on roof area, and scuppers and pipe sizing meet the tabulated limits and code rules (see **§ 1105.1** and Tables **1105.1(1)** and **1105.1(2)**).
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
Controlled‑flow roof drainage lets you size roof drainage by storing and metering storm water on the roof rather than sizing for the full storm runoff—but only when specific limits are met. Key limits include that water from a 25‑year frequency storm may not be stored on the roof for more than 24 hours, ponding depths at drains may not exceed the values in Table 1105.1(1), and each drain must have a precalibrated, fixed, proportional (notched) weir; these requirements are in § 1105.1 and § 1105.0 of the CPC.
The single most important rule: water from a 25‑year storm must not remain stored on a roof for more than 24 hours; controlled‑flow systems must limit ponding to the depths listed in Table 1105.1(1). § 1105.1
Requirements in detail
Applicability and overall limits
- The controlled‑flow option is an alternative to sizing storm drainage under Section 1103.0; it is only allowed when the conditions in § 1105.1 are satisfied. § 1105.1
- The stored volume from a 25‑year storm must be released within 24 hours. § 1105.1(1)
Number of drains and placement
- Minimum of two drains for roof areas up to 10,000 ft² (929 m²).
- One additional drain is required for each additional 10,000 ft² (929 m²) (or fraction) beyond 10,000 ft². § 1105.1(3)
Weirs and mechanical restrictions
- Each roof drain must have a precalibrated, fixed (non‑adjustable), proportional (notched) weir located in a standing water collar inside the strainer. No mechanical devices or valves are permitted for the controlled discharge. § 1105.1(4)
Pipe sizing and measurement rules
- Pipe sizing is to be based on the pre‑calibrated flow rate (gpm or L/s) of the manufacturer’s weir at the maximum allowable ponding depth, and then sized using Table 1103.1 and Table 1103.2. The code requires the designer to use the weir’s rated flow at the permitted ponding depth to select piping. § 1105.1(5)
- When measuring ponding depth, do not count the height of stones or granular ballast above the waterproofing, and the roof surface near the drain must not be recessed to create a reservoir. § 1105.1(6)
Structural live load and safety
- Roofs using controlled drainage must have a design roof live load of not less than 30 lb/ft² (146 kg/m²) so the roof’s structural capacity exceeds the 15 lb/ft² (73 kg/m²) represented by the stored water per Table 1105.1(1). § 1105.1(7)
Scuppers and parapet requirements
- Scuppers are required in parapet walls. The bottom of scuppers above the roof at the drain location may not exceed the distances shown in Table 1105.1(2). § 1105.1(8)
- Scupper openings must 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 per Table 1103.1). Flashings must extend above the top of scuppers, and 45° cants are required at walls or parapets. § 1105.1(9)–(11)
Submission and documentation
- Calculations for controlled‑flow roof drainage must be submitted to the Authority Having Jurisdiction for approval. § 1105.1(13)
Decision‑relevant values (quick reference table)
| Item | Key value / dimension | Code reference |
|---|---|---|
| Maximum storage time for a 25‑yr storm | 24 hours | § 1105.1(1) |
| Required minimum drains | 2 drains for ≤ 10,000 ft²; +1 per 10,000 ft² over | § 1105.1(3) |
| Required drain device | Precalibrated, fixed proportional (notched) weir (no valves/mechanics) | § 1105.1(4) |
| Pipe sizing basis | Use weir-rated gpm at max ponding depth → Table 1103.1/1103.2 | § 1105.1(5) |
| Max water depth — flat roof | 3 in. at drain | Table 1105.1(1) |
| Max water depth — 2 in. rise | 4 in. at drain | Table 1105.1(1) |
| Max water depth — 4 in. rise | 5 in. at drain | Table 1105.1(1) |
| Max water depth — 6 in. rise | 6 in. at drain | Table 1105.1(1) |
| Scupper bottom heights above roof level | See Table 1105.1(2) (Flat = 3 in., 2 in. rise = 4 in., 4 in. rise = 5 in., 6 in. rise = 6 in.) | Table 1105.1(2) |
| Minimum scupper opening height | 4 in. (102 mm) | § 1105.1(9) |
| Required roof live load (design) | ≥ 30 lb/ft² (146 kg/m²) | § 1105.1(7) |
Exceptions & special cases
- Setback roofs: Drains on setback roofs may connect to a controlled‑flow system only if the setback is designed for storing water, or the setback area is converted (per § 1105.0) to an equivalent gpm and the controlled‑flow piping is sized for the combined loading. Branches from roof drains not provided with controlled flow must be sized per Table 1103.1. § 1105.2
- Controlled drainage requires a secondary means of emergency drainage (see related CPC sections on secondary roof drainage and the Building Code requirements for ponding/structural checks). The Building Code also requires checking for ponding instability and providing a secondary drain elevation. (See Related provisions below.)
Common mistakes
- Installing adjustable valves, pumps, flappers, or other mechanical flow controllers instead of a precalibrated, fixed, proportional weir (this violates § 1105.1(4)).
- Measuring ponding depth including ballast, gravel, or stones (the code explicitly excludes granular ballast in depth measurement — § 1105.1(6)).
- Using fewer drains than required for the roof area (missed application of the 2 drains per 10,000 ft² rule — § 1105.1(3)).
- Not sizing horizontal and vertical piping from the manufacturer’s weir flow rating at the code maximum ponding depth, then cross‑referencing Table 1103.1/1103.2 (§ 1105.1(5)).
- Allowing a recessed “reservoir” near the drain (roof surface must not be recessed to create extra storage — § 1105.1(6)).
Worked example — concrete scenario
Scenario: Flat commercial roof, 12,000 ft², owner wants controlled‑flow design.
Number of drains: Roof ≤ 10,000 ft² requires 2 drains; for the extra 2,000 ft² add 1 drain (one per 10,000 ft² over). Required total = 3 drains. § 1105.1(3)
Maximum allowable ponding depth at each drain: For a flat roof the maximum water depth at the drain is 3 inches (Table 1105.1(1)). Use 3 in. as the design ponding depth when reading the manufacturer’s pre‑calibrated weir flow. Table 1105.1(1)
Determine weir flow and pipe size (method, not numeric here):
- Obtain the precalibrated weir manufacturer rating (gpm) for the weir when the roof has 3 in. depth. § 1105.1(4)–(5)
- For each drain, use that gpm and then select the required vertical and horizontal pipe sizes from Table 1103.1 and Table 1103.2 (these tables list pipe capacity vs. rainfall/flow). The CPC requires this step but the numeric entries of Table 1103.1 are not reproduced here; consult Table 1103.1 and the weir spec to pick pipe sizes. § 1105.1(5)
Check structural load: Confirm roof is designed for ≥ 30 lb/ft² live load so the stored water (per the ponding depth) does not exceed the code safety requirement. § 1105.1(7)
Scuppers & secondary drainage: Provide scuppers sized and located per Table 1105.1(2) and provide emergency drainage per the Building Code and CPC secondary drainage rules. § 1105.1(8)–(11)
(Important: specific weir gpm values and exact pipe sizes require the manufacturer’s weir table and Table 1103.1/1103.2; those numeric tables are necessary to complete final sizing and were not reproduced in the text excerpts used here.)
Related provisions (CPC & referenced tables)
- § 1105.0 — Controlled‑flow roof drainage scope and introductory language.
- § 1105.1 — Detailed application requirements for controlled‑flow (drains, weirs, ponding limits, live load, scuppers, documentation).
- Table 1105.1(1) — Controlled‑flow maximum roof water depth (flat, 2", 4", 6" rise).
- Table 1105.1(2) — Distance of scupper bottoms above roof level corresponding to roof rise.
- § 1105.2 — Setback roofs connection rules for controlled‑flow systems.
- § 1104.1 — Values for continuous or semi‑continuous discharges (used when combining pumped or continuous sources with storm drainage).
- § 1101.12 — Primary and secondary roof drainage requirements (secondary/emergency drainage sizing and methods).
- Table 1103.1 / Table 1103.2 — Required for final pipe sizing (use weir gpm → select pipe). These tables are referenced by § 1105.1(5) but the table contents must be consulted in the CPC for numerical selection.
Code references
Grounded in the retrieved California Plumbing Code — click a citation to read the verbatim passage:
CPC § 1103.4 High 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 § 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 § 25.4 High relevance — show source text
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
- 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.
tered design professional and approved in accordance with Section 301.5.
1106.2 Siphonic Roof Drainage Systems. The design of a siphonic roof drainage system shall comply with ASPE/ANSI 45.
1106.3 Siphonic Roof Drains. Siphonic roof drains shall comply with ASME A112.6.9.
1107.0 Testing. 1107.1 Testing Required. New building storm drainage systems and parts of existing systems that have been altered, extended, or repaired shall be tested in accordance with Section 1107.2.1 or Section 1107.2.2 to disclose leaks and
defects.
1107.2 Methods of Testing Storm Drainage Systems. Except for outside leaders and perforated or open-jointed drain tile, the piping of storm drain systems shall be tested upon completion of the rough piping installation by water or air, except that plastic pipe shall not be tested with air, and proved tight. The Authority Having Jurisdiction shall be permitted to require the removal of cleanout plugs to ascertain whether the pressure has reached parts of the system. One of the following test methods shall be used in accordance with Section 1107.2.1 through Section 1107.2.3. 1107.2.1 Water Test. After piping has been installed, the water test shall be applied to the drainage system, either to the entire system or sections. Where the test is applied to the entire system, all openings in the piping shall be tightly closed except for the highest opening, and the system shall be filled with water to the point of overflow.
CPC § 5.2 High relevance — show source text
Rainfall intensity shall be determined in inches per hour for 15-minute duration storms for the risk categories given in Table 1611 A .1. The ponding head shall be based on structural analysis as the depth of water due to deflections of the roof subjected to unfactored rain load and unfactored dead load.
Equation 16 A -20 R = 5.2( d s + d h + d p ) For SI: R = 0.0098( d s + d h + d p )
where:
d h = Hydraulic head equal to the depth of water on the undeflected roof above the inlet of the secondary drainage system for structural loading (SDSL) required to achieve the design flow, in inches (mm). d p = Ponding head equal to the depth of water due to deflections of the roof subjected to unfactored rain load and unfactored dead load, in inches (mm).
d s = Static head equal to the depth of water on the undeflected roof up to the inlet of the secondary drainage system for structural loading (SDSL), in inches (mm). R = Rain load, in pounds per square foot (kN/m [2] ).
16A-32 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
STRUCTURAL DESIGN
SDSL is the roof drainage system through which water is drained from the roof when the drainage systems listed in ASCE 7 Section 8.2 (a) through (d) are blocked or not working.
TABLE 1611A.1—DESIGN STORM RETURN PERIOD BY RISK CATEGORY Col2 RISK CATEGORY DESIGN STORM RETURN PERIOD I & II 100 years III 200 years IV 500 years 1611 A .2 Ponding instability. Ponding instability on roofs shall be evaluated in accordance with ASCE 7.
1611 A .3 Controlled drainage. Roofs equipped with hardware to control the rate of drainage shall be equipped with a secondary drainage system at a higher elevation that limits accumulation of water on the roof above that elevation. Such roofs shall be designed to sustain the load of rainwater that will accumulate on them to the elevation of the secondary drainage system plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow determined from Section 1611 A .1. Such roofs shall be checked for ponding instability in accordance with Section 1611 A .2.
SECTION 1612 A —FLOOD LOADS
1612 A .1 General. Within flood hazard areas as established in Section 1612 A .3, all new construction of buildings, structures and portions of buildings and structures, including substantial improvement and restoration of substantial damage to buildings and structures, shall be designed and constructed to resist the effects of flood hazards and flood loads. For buildings that are located in more than one flood hazard area, the provisions associated with the most restrictive flood hazard area shall apply.
CPC § 1101.16 High relevance — show source text
1101.16 Leaders, Conductors, and
Connections . . . . . . . . . . . . . . . . .207
1102.0 Roof Drains . . . . . . . . . . . . . . . . . .207
1102.1 Applications . . . . . . . . . . . . . . . . .207
1102.2 Dome Strainers Required . . . . . . .207
1102.3 Roof Drain Flashings . . . . . . . . . .207
1103.0 Size of Leaders, Conductors,
and Storm Drains . . . . . . . . . . . . .207
1103.1 Vertical Conductors and
Leaders . . . . . . . . . . . . . . . . . . . . .207
1103.2 Size of Horizontal Storm
Drains and Sewers . . . . . . . . . . . .207
1103.3 Size of Roof Gutters . . . . . . . . . . .207
1103.4 Side Walls Draining onto a Roof . . . . . . . . . . . . . . . . . .207
Table 1103.1 Sizing Roof Drains, Leaders, and Vertical Rainwater Piping . . .208
1104.0 Values for Continuous Flow . . . . .208
1104.1 General . . . . . . . . . . . . . . . . . . . . .208
1105.0 Controlled-Flow Roof
Drainage . . . . . . . . . . . . . . . . . . . .208
1105.1 Application . . . . . . . . . . . . . . . . . .208
Table 1105.1(1) Controlled-Flow Maximum Roof Water Depth . . . . . . . . . . . . .209
Table 1105.1(2) Distance of Scupper Bottoms Above Roof . . . . . . . . . . . . . . . . . .209
xxxviii 2025 CALIFORNIA PLUMBING CODE
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TABLE OF CONTENTS
1105.2 Setback Roofs . . . . . . . . . . . . . . .209
1106.0 Engineered Storm Drainage System . . . . . . . . . . . . . . . . . . . . .209
1106.1 General . . . . . . . . . . . . . . . . . . . . .209
1106.2 Siphonic Roof Drainage Systems . . . . . . . . . . . . . . . . . . . .209
1106.3 Siphonic Roof Drains . . . . . . . . . .209
1107.0 Testing . . . . . . . . . . . . . . . . . . . . .209
1107.1 Testing Required . . . . . . . . . . . . .209
1107.2 Methods of Testing Storm Drainage Systems . . . . . . . . . . . .209
Table 1103.2 Sizing of Horizontal Rainwater Piping . . . . . . . . . . . . .210
Table 1103.3 Size of Gutters . . . . . . . . . . . . . . .211
CPC § 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 § 8.2 Medium relevance — show source text
STRUCTURAL DESIGN
R = Rain load, in pounds per square foot (kN/m [2] ).
SDSL is the roof drainage system through which water is drained from the roof when the drainage systems listed in ASCE 7 Section 8.2 (a) through (d) are blocked or not working.
TABLE 1611.1—DESIGN STORM RETURN PERIOD BY RISK CATEGORY Col2 RISK CATEGORY DESIGN STORM RETURN PERIOD I & II 100 years III 200 years IV 500 years 1611.2 Ponding instability. Ponding instability on roofs shall be evaluated in accordance with ASCE 7.
1611.3 Controlled drainage. Roofs equipped with hardware to control the rate of drainage shall be equipped with a secondary drainage system at a higher elevation that limits accumulation of water on the roof above that elevation. Such roofs shall be designed to sustain the load of rainwater that will accumulate on them to the elevation of the secondary drainage system plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow determined from Section 1611.1. Such roofs shall be checked for ponding instability in accordance with Section 1611.2.
SECTION 1612—FLOOD LOADS
1612.1 General. Within flood hazard areas as established in Section 1612.3, all new construction of buildings, structures and portions of buildings and structures, including substantial improvement and restoration of substantial damage to buildings and structures, shall be designed and constructed to resist the effects of flood hazards and flood loads. For buildings that are located in more than one flood hazard area, the provisions associated with the most restrictive flood hazard area shall apply.
1612.2 Design and construction. The design and construction of buildings and structures located in flood hazard areas, including coastal high hazard areas and coastal A zones, shall be in accordance with Chapter 5 of ASCE 7 and ASCE 24. Elevators, escalators, conveying systems and their components shall conform to ASCE 24 and ASME A17.1/CSA B44 as applicable.
Exception: Temporary structures complying with Section 3103.6.1.3.
1612.3 Establishment of flood hazard areas. To establish flood hazard areas, the applicable governing authority shall adopt a flood hazard map and supporting data. The flood hazard map shall include, at a minimum, areas of special flood hazard as identified by the Federal Emergency Management Agency in an engineering report entitled “The Flood Insurance Study for [ INSERT NAME OF JURISDIC -
TION ],” dated [ INSERT DATE OF ISSUANCE ], as amended or revised with the accompanying Flood Insurance Rate Map (FIRM) and Flood Boundary and Floodway Map (FBFM) and related supporting data along with any revisions thereto. The adopted flood hazard map and supporting data are hereby adopted by reference and declared to be part of this section.
Exception: [OSHPD 1R, 2 & 5] The flood hazard map shall include, at a minimum, areas of special flood hazard as identified by the Federal Emergency Management Agency’s Flood Insurance Study (FIS) adopted by the local authority having jurisdiction where the project is located.
CPC § 1611A.1 Medium relevance — show source text
TABLE 1611A.1—DESIGN STORM RETURN PERIOD BY RISK CATEGORY Col2 RISK CATEGORY DESIGN STORM RETURN PERIOD I & II 100 years III 200 years IV 500 years 1611 A .2 Ponding instability. Ponding instability on roofs shall be evaluated in accordance with ASCE 7.
1611 A .3 Controlled drainage. Roofs equipped with hardware to control the rate of drainage shall be equipped with a secondary drainage system at a higher elevation that limits accumulation of water on the roof above that elevation. Such roofs shall be designed to sustain the load of rainwater that will accumulate on them to the elevation of the secondary drainage system plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow determined from Section 1611 A .1. Such roofs shall be checked for ponding instability in accordance with Section 1611 A .2.
SECTION 1612 A —FLOOD LOADS
1612 A .1 General. Within flood hazard areas as established in Section 1612 A .3, all new construction of buildings, structures and portions of buildings and structures, including substantial improvement and restoration of substantial damage to buildings and structures, shall be designed and constructed to resist the effects of flood hazards and flood loads. For buildings that are located in more than one flood hazard area, the provisions associated with the most restrictive flood hazard area shall apply.
1612 A .2 Design and construction. The design and construction of buildings and structures located in flood hazard areas, including coastal high hazard areas and coastal A zones, shall be in accordance with Chapter 5 of ASCE 7 and ASCE 24. Elevators, escalators, conveying systems and their components shall conform to ASCE 24 and ASME A17.1/CSA B44 as applicable.
Exception: Temporary structures complying with Section 3103.6.1.3.
1612 A .3 Establishment of flood hazard areas. To establish flood hazard areas, the applicable governing authority shall adopt a flood hazard map and supporting data. The flood hazard map shall include, at a minimum, areas of special flood hazard as identified by the Federal Emergency Management Agency’s Flood Insurance Study (FIS) adopted by the local authority having jurisdiction where the project is located, as amended or revised with the accompanying Flood Insurance Rate Map ( FIRM ) and Flood Boundary and Flood- way Map (FBFM) and related supporting data along with any revisions thereto. The adopted flood hazard map and supporting data are hereby adopted by reference and declared to be part of this section.
1612 A .3.1 Design flood elevations. Where design flood elevations are not included in the flood hazard areas established in Section 1612 A .3, or where floodways are not designated, the building official is authorized to require the applicant to do one of the following:
- Obtain and reasonably utilize any design flood elevation and floodway data available from a federal, state or other
source.
- Determine the design flood elevation or floodway in accordance with accepted hydrologic and hydraulic engineering practices used to define special flood hazard areas. Determinations shall be undertaken by a registered design professional who shall document that the technical methods used reflect currently accepted engineering practice.
California Plumbing Code Medium relevance — show source text
(feet)|FAN|FAN|NAT|FAN|FAN|NAT|FAN|FAN|NAT|FAN|FAN|NAT|FAN|FAN|NAT| |HEIGHT
H
(feet)|LATERAL
L
(feet)**|Min|Max|Max|Min|Max|Max|Min|Max|Max|Min|Max|Max|Min|Max|Max| |6|0
2
4
6|0
53
79
93|698
425
419
413|370
285
279
273|0
63
93
110|897
543
536
530|470
370
362
354|0
75
110
128|1121
675
668
661|570
455
445
435|0
103
147
171|1645
982
975
967|850
650
640
630|0
138
191
219|2267
1346
1338
1330|1170
890
880
870| |8|0
2
5
8|0
50
83
99|780
483
473
463|415
322
313
303|0
60
99
117|1006
619
607
596|537
418
407
396|0
71
115
137|1261
770
758
746|660
515
503
490|0
98
154
180|1858
1124
1110
1097|970
745
733
720|0
130
199
231|2571
1543
1528
1514|1320
1020
1010
1000| |10|0
2
5
10|0
48
81
104|847
533
522
504|450
355
346
330|0
57
95
122|1096
684
671
651|585
457
446
427|0
68
112
142|1377
852
839
817|720
560
547
525|0
93
149
187|2036
1244
1229
1204|1060
850
829
795|0
124
192
238|2825
1713
1696
1669|1450
1130
1105
1080| |15|0
2
5California Plumbing Code Medium relevance — show source text
2
5
10
15|0
45
76
99
115|970
633
620
600
580|525
414
403
386
373|0
53
90
116
134|1263
815
800
777
755|682
544
529
507
491|0
63
105
135
155|1596
1019
1003
977
953|840
675
660
635
610|0
86
140
177
202|2380
1495
1476
1446
1418|1240
985
967
936
905|0
114
182
227
257|3323
2062
2041
2009
1976|1720
1350
1327
1289
1250| |20|0
2
5
10
15
20|0
41
73
95
111
125|1057
711
697
675
654
634|575
470
460
443
427
410|0
50
86
112
129
145|1384
917
902
877
853
830|752
612
599
576
557
537|0
59
101
130
150
167|1756
1150
1133
1105
1078
1052|930
755
738
710
688
665|0
81
135
172
195
217|2637
1694
1674
1641
1609
1578|1350
1100
1079
1045
1018
990|0
107
174
220
248
273|3701
2343
2320
2282
2245
2210|1900
1520
1498
1460
1425
1390| |30|0
2
5
10
15
20
30|0
33
69
91
105
119
149|1173
826
811
788
765
743
702|650
535
524
507
490
473
444|0
42
82
107
124
139
171|1548
1072
1055
1028
1002
977
929|855
700
688
668
648
628
594|0
54
96
125
143
160
195|1977
1351
1332
1301
1272
1243
1189|1060
865
851
829
807
784
745|0California Plumbing Code Medium relevance — show source text
50
83
99|780
483
473
463|415
322
313
303|0
60
99
117|1006
619
607
596|537
418
407
396|0
71
115
137|1261
770
758
746|660
515
503
490|0
98
154
180|1858
1124
1110
1097|970
745
733
720|0
130
199
231|2571
1543
1528
1514|1320
1020
1010
1000| |10|0
2
5
10|0
48
81
104|847
533
522
504|450
355
346
330|0
57
95
122|1096
684
671
651|585
457
446
427|0
68
112
142|1377
852
839
817|720
560
547
525|0
93
149
187|2036
1244
1229
1204|1060
850
829
795|0
124
192
238|2825
1713
1696
1669|1450
1130
1105
1080| |15|0
2
5
10
15|0
45
76
99
115|970
633
620
600
580|525
414
403
386
373|0
53
90
116
134|1263
815
800
777
755|682
544
529
507
491|0
63
105
135
155|1596
1019
1003
977
953|840
675
660
635
610|0
86
140
177
202|2380
1495
1476
1446
1418|1240
985
967
936
905|0
114
182
227
257|3323
2062
2041
2009
1976|1720
1350
1327
1289
1250| |20|0
2
5
10
15
20|0
41
73
95
111
125|1057
711
697
675
654
634|575
470
460
443
427
410|0
50
86
112
129
145|1384
917
902
877
853
830|752
612
599
576
557
537|0
Frequently asked questions
Can I use a motorized valve or pump to control roof drainage?
No. The CPC requires a precalibrated, fixed, proportional (notched) weir in a standing water collar inside the strainer; mechanical devices or valves are not permitted for controlled‑flow drains. § 1105.1(4)
How deep can water pond on a flat roof under controlled flow?
Maximum water depth at the drain for a flat roof is 3 inches, per Table 1105.1(1).
How many drains do I need for a 25,000 ft² roof using controlled flow?
Minimum of 2 drains for the first 10,000 ft², plus 1 additional drain for each additional 10,000 ft² (or fraction). For 25,000 ft² that equals 2 + 2 = 4 drains. § 1105.1(3)
Do I include gravel or ballast when measuring ponding depth?
No. The height of stones or other granular material above the waterproofed surface is not considered in the water depth measurement. § 1105.1(6)
What must I submit to the building official?
Calculations for the roof drainage system (including controlled‑flow calculations and pipe sizing based on the weir ratings) must be submitted for approval. § 1105.1(13)
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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