CBC · California Building Code

How must roof drainage and secondary (emergency overflow) drains be provided and sized?

If a parapet or raised roof edge can trap water, the CBC requires secondary (emergency) roof drains or scuppers sized and placed so ponding never exceeds the roof’s design depth; secondary inlets are typically set 2 inches above the roof and scuppers must be at least 4 inches high — hydraulic sizing and storm intensity come from the California Plumbing Code (Chapter 11) and structural ponding checks from CBC §1611.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

Where roof drains are required the California Building Code mandates provision of secondary (emergency overflow) drains or scuppers wherever the roof perimeter or parapet can trap water if the primary drains fail; the design and installation must follow Chapter 15 (roof drainage), Section 1611 (structural ponding/roof drainage) and Chapter 11 of the California Plumbing Code (storm drainage) for sizing and installation. Primary drainage sizing is coordinated with structural design and the plumbing rules; secondary drains must be located and sized so ponding will not exceed the depth for which the roof was designed (see §1502.1 and §1502.2).

Requirements in detail

Basic obligation and where it applies

  • The CBC requires secondary (emergency overflow) roof drains or scuppers whenever the roof perimeter construction “extends above the roof in such a manner that water will be entrapped” if primary drains become blocked — so check parapets, raised copings, and any curb/edge details that can form a trap (§1502.2).

  • Section 1502.1 ties roof drainage design and installation to Section 1611 (ponding and structural checks) and Chapter 11 of the California Plumbing Code (CPC) — so the CBC establishes the requirement and defers sizing and hydraulic rules to CPC and the structural provisions in §1611.

How secondary drainage may be provided (methods)

  • Scuppers / open-sided roof: provide open scuppers or an open-sided roof where the parapet would trap water. Scuppers must be sized and located so that ponding depth does not exceed the roof’s design depth; scupper openings shall be not less than 4 inches high and the scupper width shall equal the circumference of the roof drain required for the area served (sized per CPC Table 1103.1). These requirements are in the plumbing code chapter referenced by the CBC.

  • Secondary roof drain (standby inlet): provide one or more secondary roof drains with inlet flow lines located not less than 2 inches above the roof surface (so they act only when primary drains are blocked), and sized per CPC/Section 1611 so that ponding remains within the structural design limits. The secondary drain’s maximum inlet elevation is the elevation that prevents ponding deeper than the roof’s design depth.

  • Two piping options for secondary drains in the CPC:

    • Separate piping system: the secondary roof drain(s) discharge to a separate piping system that is independent of the primary system; the outlet should be observable (above grade) and the secondary system sized in accordance with primary-sizing rules for the same rainfall rate (§1101.12.2.2.1).
    • Combined system: the secondary drains may tie into the primary vertical conductor downstream of the last horizontal offset below the roof; if combined, the vertical/horizontal system must be sized based on double the local rainfall rate used for the primary system (i.e., capacity for combined flow) (§1101.12.2.2.2).

Sizing basis and reference storm

  • The CPC directs primary roof drainage (drains, gutters, leaders and horizontal storm drains) to be sized based on a 60‑minute duration storm at the 100‑year return period unless the AHJ requires otherwise; refer to the local rainfall intensity tables (CPC Table D101.1 or the local required source) to determine the inches/hour intensity used for sizing. The CBC requires designers to use Section 1611 plus Chapter 11 CPC for hydraulic and structural determinations.

Residential variant (prescriptive)

  • For roofs governed by the California Residential Code, overflow drains may be either:
    • overflow drains sized the same as the roof drains with the inlet flow line located 2 inches above the low point, OR
    • overflow scuppers having three times the size of the roof drains with a minimum opening height of 4 inches, with the scupper inlet located 2 inches above the low point. The installation and sizing must comply with the California Plumbing Code. (§R903.4.1)

Decision-relevant dimensions / values

Item Decision value you must apply Code Reference
When secondary drainage is required Where parapet/perimeter can entrap water (any condition that would trap water if primary drains fail) §1502.2
Secondary inlet elevation (minimum above roof surface / low point) 2 inches (51 mm) above the roof surface/low point for secondary roof drains or overflow inlets §1101.12.2.2 and §R903.4.1
Minimum scupper opening height 4 inches (102 mm) §1101.12.2.1 and §R903.4.1
Scupper width when sized to match drain Width = circumference of required roof drain (sized per Table 1103.1) §1101.12.2.1
Primary drainage design storm 60‑minute duration, 100‑year return (unless AHJ requires otherwise) — use local intensity tables (Table D101.1) §1101.12.1
Combined-system sizing requirement If secondary connects into primary vertical below the roof, size system for double the local rainfall rate §1101.12.2.2.2
Sizing standard for ponding/structural checks Use Section 1611 (ponding head and structural capacity) when determining allowable ponding depth and SDSL (structural drainage load) §1502.1 and §1611

Exceptions & special cases

  • Reroof work: recovering or replacing an existing low‑slope roof that already provides positive roof drainage and meets Sections 1608.3 and 1611.2 may be exempt from installing new secondary drains/scuppers required by §1502.2 (i.e., do not force new overflow devices on certain reroofs). However, existing required secondary systems must not be removed unless replaced in conformance with §1502.2. See the reroofing/alteration exceptions.

  • Controlled‑flow or engineered systems: where controlled hardware or siphonic systems are used, follow the engineered design guides (CPC §1106 and ASPE/ANSI standards) and include a secondary system at a higher elevation as required by Section 1611A for controlled drainage. The CBC defers these detailed hydraulic designs to CPC/ASCE/ANSI referenced standards.

  • Separate-discharge secondary systems must discharge to a location observable by occupants/maintenance (above grade) and be sized using the same rainfall rate used for the primary system; combined systems change the sizing basis (double the rate). Confirm with AHJ for acceptable discharge locations.

Common mistakes

  • Placing overflow/scupper inlet too low (less than 2" above roof low point) — secondary inlets must be set so they operate only when primary drains are blocked (CPC requires 2 inches).
  • Undersizing scuppers (less than 4" height) or not matching scupper width to the required drain circumference.
  • Combining secondary into primary without increasing capacity; combined systems must be sized for double the local rainfall rate.
  • Forgetting to coordinate hydraulic sizing with structural ponding capacity — the secondary inlet elevation and allowable ponding must keep water within the roof’s design depth per Section 1611.
  • Removing existing secondary drains during reroofing where the exception does not apply; follow reroofing exceptions closely.

Worked example — concrete scenario (methodology; note where code tables are used)

This example shows the method you must follow; the CPC sizing tables and local rainfall intensities are required inputs (those tables are not reproduced here).

Scenario:

  • Flat commercial roof area = 2,000 ft².
  • Assume (hypothetical example only — you must obtain the actual local rainfall intensity from CPC Table D101.1 or AHJ): design rainfall intensity = 2.5 in/hr (60‑minute storm, 100‑year) for demonstration.

Step 1 — determine design flow rate to roof drains:

  • Convert intensity to feet per hour: 2.5 in/hr = 2.5 / 12 = 0.2083 ft/hr.
  • Volumetric flow = intensity (ft/hr) × area (ft²) = 0.2083 × 2,000 = 416.7 ft³/hr.
  • Convert to gallons per minute (gpm): 1 ft³ = 7.4805 gallons; 416.7 ft³/hr × 7.4805 = 3,119 gal/hr. Divide by 60 → ~52.0 gpm.

Step 2 — size primary drain(s) using CPC tables:

  • Use CPC Table 1103.1 (and applicable tables) to select a roof drain and leader/pipe size that can pass ~52 gpm for this roof area and slope. The CPC and Table 1103.1 provide the standard pipe diameter/capacity selections; consult the table and the AHJ.

Step 3 — provide secondary (emergency) drainage per code:

  • Option A — secondary overflow drain(s): install secondary drains with inlet flow line located 2" above the roof surface/low point (per §1101.12.2.2); size the secondary system in accordance with the same rainfall rate used for the primary (i.e., sized for 2.5 in/hr in this example) if the secondary is on a separate independent discharge. If you elect separate piping, route to an above‑grade observable discharge per §1101.12.2.2.1.
  • Option B — scuppers / residential-style overflow: provide scuppers with minimum 4" opening height; scupper width must equal the circumference of the roof drain required for the area served (for prescriptive residential, scuppers may be 3× the roof drain size with 4" minimum height and inlet at 2"). Verify which option applies by occupancy/type and local practice.

Step 4 — combined system check (if tying secondary into primary):

  • If you tie the secondary into the primary vertical below the roof (combined system), size the combined vertical/horizontal system for double the local rainfall rate (i.e., design as if rainfall intensity = 5.0 in/hr in our hypothetical) per §1101.12.2.2.2. That will change required pipe diameters; consult CPC Table 1103.1 for the doubled-rate capacities.

Step 5 — structural/ponding verification:

  • Check Section 1611 (ponding/structural) to ensure the roof structure can safely carry any allowable ponding head associated with the selected secondary inlet elevation (SDSL and ponding head calculations per §1611). If ponding depth resulting from inlet elevation exceeds roof design, adjust inlet elevations or increase drain capacity.

Important: the numeric gpm and pipe sizes selected in Step 2/3 must be confirmed against the CPC tables (Table 1103.1 and local intensity Table D101.1). Those tables are required design references and are part of the plumbing code chapter referenced by the CBC.

Related provisions (selected)

  • §1502.1 (Roof drainage design and compliance with §1611 and CPC Chapter 11) — CBC.
  • §1502.2 (Secondary/emergency overflow drains or scuppers required where water can be entrapped) — CBC.
  • §1611 (Structural design — ponding and SDSL checks) — CBC (referenced for allowable ponding/structural checks).
  • §1101.12.1 (Primary roof drainage sizing: 60‑minute, 100‑year default) — California Plumbing Code (Chapter 11).
  • §1101.12.2 (Secondary drainage methods: scuppers or secondary drains) — California Plumbing Code.
  • §1101.12.2.2.1 (Separate piping system requirements for secondary drains) — California Plumbing Code.
  • §1101.12.2.2.2 (Combined system sizing — double rainfall rate) — California Plumbing Code.
  • §R903.4.1 (Residential prescriptive overflow sizing options: equal-size overflow drain at 2" or 3× scupper with 4" min) — California Residential Code.
  • Reroofing exceptions referencing §1502.2 (when secondary drains/scuppers are not required for certain recover/replacement situations) — California Existing Building Code / CBC exceptions.

Code references

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

  • CBC § 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.

  • CBC § 1101.12.2.2 High relevance — show source text

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

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

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    STORM DRAINAGE

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

    based on the rainfall rate for which the primary system is sized. 1101.12.2.2.2 Combined System. The secondary roof drains shall connect to the vertical piping of the primary storm drainage conductor downstream of the last horizontal offset located below the roof. The primary storm drainage system shall connect to the building storm water that connects to an underground public storm sewer. The combined secondary and primary roof drain systems shall be sized in accordance with Section 1103.0 based on double the rain fall rate for the local area.

    1101.13 Cleanouts. Cleanouts for building storm drains shall comply with the requirements of Section 719.0 of this code.

    1101.13.1 Rain Leaders and Conductors. Rain leaders and conductors connected to a building storm sewer shall have a cleanout installed at the base of the

    leader or conductor before it connects to the horizontal

    drain.

    1101.14 Rainwater Sumps. Rainwater sumps serving “public use” occupancy buildings shall be provided with dual pumps arranged to function alternately in the case of overload or mechanical failure. Pumps rated 600 V or less shall comply with UL 778 and shall be installed in accordance with the manufacturer’s installation instructions.

    1101.15 Traps on Storm Drains and Leaders. Leaders and storm drains, where connected to a combined sewer, shall be trapped. Floor and area drains connected to a storm drain shall be trapped.

    Exception: Traps shall not be required where roof drains, rain leaders, and other inlets are at locations permitted under Section 906.0, Vent Termination.

    1101.15.1 Where Not Required. No trap shall be required for leaders or conductors that are connected to a sewer carrying storm water exclusively. 1101.15.2 Trap Size. Traps, where installed for individual conductors, shall be the same size as the horizontal drain to which they are connected.

    1101.15.3 Method of Installation of Combined Sewer. Individual storm-water traps shall be installed on the stormwater drain branch serving each storm-water inlet, or a single trap shall be installed in the main storm drain just before its connection with the combined building sewer. Such traps shall be provided with an accessible cleanout on the outlet side of the trap.

  • CBC § 1501.1 High 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.

  • CBC § 2.1 High 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).

  • CBC § 1101.7 High relevance — show source text

    (1) They do not serve continuously flowing springs or groundwater.

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

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

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

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

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

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

  • CBC § 1502.2 High 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.

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    15-2 2025 CALIFORNIA BUILDING CODE

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    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 .

  • CBC § 106.2.1 High relevance — show source text

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

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

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

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

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

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    CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE

    APPENDIX L - SUSTAINABLE PRACTICES

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

  • CBC § 702.7 High relevance — show source text

    702.7 Materials and methods. New work shall comply with the materials and methods requirements in the California Building Code, California Energy Code, California Mechanical Code and California Plumbing Code, as applicable, that specify material standards, detail of installation and connection, joints, penetrations and continuity of any element, component or system in the building.

    SECTION 703—FIRE PROTECTION

    703.1 General. Alterations shall be done in a manner that maintains the level of fire protection provided.

    703.2 Fire alarm and detection.

    703.2.1 Replacement devices, combinations of devices, appliances, and equipment shall be listed and approved.

    703.2.2 Systems out of service. Existing fire alarm and detection systems shall be maintained in accordance with Section 901.7 of the California Fire Code, C.C.R. Title 24, Part 9.

    703.3 Construction in existing buildings. On-site fire protection during construction shall be in accordance with Chapter 33 of the Cali- fornia Building Code, C.C.R. Title 24, Part 2, and California Fire Code, C.C.R. Title 24, Part 9.

    SECTION 704—MEANS OF EGRESS

    704.1 General. Alterations shall be done in a manner that maintains the level of protection provided for the means of egress.

    704.2 Casework. Addition, alteration or reconfiguration of nonfixed and movable cases, counters and partitions not over 5 feet 9 inches (1753 mm) in height shall maintain the required means of egress path.

    704.3 Locking arrangements in educational occupancies. In Group E occupancies, Group B educational occupancies and Group I4 occupancies, egress doors with locking arrangements designed to keep intruders from entering the room shall comply with Section 1010.2.7 of the California Building Code .

    SECTION 705—REROOFING

    [BS] 705.1 General. Materials and methods of application used for recovering or replacing an existing roof covering shall comply with the requirements of Chapter 15 of the California Building Code .

    Exceptions:

    1. Roof replacement or roof recover of existing low-slope roof coverings shall not be required to meet the minimum design slope requirement of [1] / 4 unit vertical in 12 units horizontal (2-percent slope) in Section 1507 of the California Building Code for roofs that provide positive roof drainage and meet the requirements of Sections 1608.3 and 1611.2 of the Cali- fornia Building Code .
    2. Recovering or replacing an existing roof covering shall not be required to meet the requirement for secondary (emergency overflow) drains or scuppers in Section 1502 of the California Building Code for roofs that provide for positive roof drainage and meet the requirements of Sections 1608.3 and 1611.2 of the California Building Code . For the purposes of this exception, existing secondary drainage or scupper systems required in accordance with this code shall not be removed unless they are replaced by secondary drains or scuppers designed and installed in accordance with Section 1502 of the California Building Code .

    [BS] 705.2 Roof replacement. Roof replacement shall include the removal of all existing layers of roof coverings down to the roof deck.

  • CPC § 2025 High relevance — show source text

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    FORMAT OF THE UNIFORM PLUMBING CODE

    Chapter 10 Traps and Interceptors.

    Chapter 10 regulates the material, design, and installation of traps, interceptors, and separators. Traps are required on drainage type plumbing fixtures and must be self-scouring without interior partitions. Interceptors, on the other hand, are designed to control what goes down a drain. Interceptors are used to keep harmful substances from entering the sanitary drainage system, such as grease, sand, oil and other materials. The retained materials need periodic removal to maintain efficiency and function of the separating device. The capacity of an interceptor is based on retention and flow rate. There are many types of interceptors that are used at beauty salons, hospitals, meat, fish or foul packaging, refineries, repair garages, gas stations, car washing facilities, various plants, factories, and processing sites. The designer of the building is responsible for locating interceptors with the expectation for the frequency of maintenance, ease of cleaning and floor space for equipment.

    Chapter 11 Storm Drainage.

    Chapter 11 regulates the removal of stormwater from roofs, yards, paved areas, and similar areas. The objective of storm drainage systems is to provide a conduit or channel through which runoff will be carried from a point of collection to a point of disposal; this protects the property and the public from the uncontrolled flow of runoff and ensures that drains and inlets are adequately sized to receive the volume of runoff that flows to the drains. For the purpose of system design, it’s necessary to specify the duration of a selected storm. All methods used to determine volumes and peak flow use historical data. Drain location must be coordinated with the architectural design of the building. When selecting the type of roof drain to use, the roof construction and its thickness, along with the intended use of the roof, are required. Where the roof perimeter extends above the roof in such a manner that water is entrapped and causes ponding, or if any portion of the roof is designed so water can pond, secondary drainage is required. Where secondary drainage is required, scuppers, or a secondary system of roof drains and pipes, are installed to prevent the accumulation of excessive rainwater.

    Chapter 12 Fuel Gas Piping.

    Chapter 12 regulates the installation of gas piping in a building, structure or within the property lines of buildings up to 5 psi. Gas piping systems must supply the minimum volume of gas required by each gas appliance to perform their proper operation under working conditions without exceeding the maximum pressure specified by each manufacturer. Because of the hazards associated with fuel gas, it is important to ensure the gas system has been inspected and tested, and that it is safe to turn on the gas supply to the building.

    Chapter 13 Health Care Facilities and Medical Gas and Medical Vacuum Systems.

    Chapter 13 regulates the installation, inspection, testing, maintenance, performance, and safe practices for medical gas and vacuum systems located in health care facilities. This chapter addresses the installation and maintenance of health care fixtures, devices, and equipment. The purpose of medical gas and medical vacuum systems is to provide safe and sufficient flows at required pressures to the medical gas outlet or vacuum inlet terminals. System design and layout should allow convenient access by the medical staff to outlet and inlet terminals, valves, and equipment during patient care or emergencies, as safety is of primary concern.

    Chapter 14 Firestop Protection.

  • CBC § 105.5 High relevance — show source text

    shall be sized to accommodate the flow of the rainwater entering the tank and not less than the aggregate crosssectional area of the inflow pipes. K 105.5 Animals and Insects. Rainwater tank openings to the atmosphere shall be protected to prevent the entrance of insects, birds, or rodents into the tank.

    K 105.6 Human Access. Rainwater tank access openings exceeding 12 inches (305 mm) in diameter shall be secured to prevent tampering and unintended entry by either a lockable device or other approved method. K 105.7 Exposure to Sunlight. Rainwater tank openings shall not be exposed to direct sunlight.

    K 105.8 Inlets. A device or arrangement of fittings shall be installed at the inlet of the tank to prevent rainwater from disturbing sediment as it enters the tank. K 105.9 Primary Tank Outlets. The primary tank outlet shall be located not less than 4 inches (102 mm) above the bottom of the tank, or shall be provided with a floating inlet to draw water from the cistern just below the water surface. K 105.10 Storage Tank Venting. Where venting using drainage or overflow piping is not provided or is considered insufficient, a vent shall be installed on each tank. The vent shall extend from the top of the tank and terminate not less than 6 inches (152 mm) above grade and shall be not less than 1 [1] ⁄ 2 inches (40 mm) in diameter. The vent terminal shall be directed downward and covered with a [3] ⁄ 32 of an inch (2.4 mm) mesh screen to prevent the entry of vermin and insect.

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

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

    K 106.0 Freeze Protection.

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

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

  • CBC § 704.3 High relevance — show source text

    704.3 Locking arrangements in educational occupancies. In Group E occupancies, Group B educational occupancies and Group I4 occupancies, egress doors with locking arrangements designed to keep intruders from entering the room shall comply with Section 1010.2.7 of the California Building Code .

    SECTION 705—REROOFING

    [BS] 705.1 General. Materials and methods of application used for recovering or replacing an existing roof covering shall comply with the requirements of Chapter 15 of the California Building Code .

    Exceptions:

    1. Roof replacement or roof recover of existing low-slope roof coverings shall not be required to meet the minimum design slope requirement of [1] / 4 unit vertical in 12 units horizontal (2-percent slope) in Section 1507 of the California Building Code for roofs that provide positive roof drainage and meet the requirements of Sections 1608.3 and 1611.2 of the Cali- fornia Building Code .
    2. Recovering or replacing an existing roof covering shall not be required to meet the requirement for secondary (emergency overflow) drains or scuppers in Section 1502 of the California Building Code for roofs that provide for positive roof drainage and meet the requirements of Sections 1608.3 and 1611.2 of the California Building Code . For the purposes of this exception, existing secondary drainage or scupper systems required in accordance with this code shall not be removed unless they are replaced by secondary drains or scuppers designed and installed in accordance with Section 1502 of the California Building Code .

    [BS] 705.2 Roof replacement. Roof replacement shall include the removal of all existing layers of roof coverings down to the roof deck.

    Exceptions:

    1. Where the existing roof assembly includes an ice barrier membrane that is adhered to the roof deck and the existing sheathing is not water-soaked or deteriorated to the point that it is not adequate as a base for additional roofing, the existing ice barrier membrane shall be permitted to remain in place and covered with an additional layer of ice barrier membrane in accordance with Section 1507 of the California Building Code where permitted by the roof-covering manufacturer and new ice-barrier underlayment manufacturer.

    7-4 2025 CALIFORNIA EXISTING BUILDING CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    ALTERATIONS—LEVEL 1

    1. Where the existing roof includes a self-adhered underlayment and the existing sheathing is not water-soaked or deteriorated to the point that it is not adequate as a base for additional roofing, the existing self-adhered underlayment shall be permitted to remain in place and covered with an underlayment complying with Tables 1507.1.1(1), 1507.1.1(2) and 1507.1.1(3) of the California Building Code .
    2. Where the existing roof includes one layer of self-adhered underlayment and the existing layer cannot be removed without damaging the roof deck, a second layer of self-adhered underlayment is permitted to be installed over the existing self-adhered underlayment provided all of the following conditions are met: 3.1. It is permitted by the roof-covering manufacturer and self-adhered underlayment manufacturer. 3.2. The existing sheathing is not water-soaked or deteriorated to the point that it is not adequate as a base for additional roofing. 3.3.
  • CBC § 1511.10.1 Medium relevance — show source text

    1511.10.1 Design. [BSC, DSA-SS, DSA-SS/CC, HCD 1 & HCD 2, OSHPD 1, 1R, 2, 4 & 5] Supports and attachments of photovoltaic panels to the roof structure, the panels, modules and components shall be designed in accordance with this code. 1. Seismic design shall be in accordance with ASCE 7 Section 13.6.12. 2. Wind design pressures shall be determined from ASCE 7 Section 29.4.3 or 29.4.4 using effective wind area in accordance with ASCE 7 Section 26.2.

    Construction documents for the supports and attachments shall be submitted to the enforcement agency for approval.

    SECTION 1512—REROOFING

    1512.1 General. Materials and methods of application used for recovering or replacing an existing roof covering shall comply with the requirements of Chapter 15.

    Exceptions:

    1. Roof replacement or roof recover of existing low-slope roof coverings shall not be required to meet the minimum design slope requirement of [1] / 4 unit vertical in 12 units horizontal (2-percent slope) in Section 1507 for roofs that provide positive roof drainage and meet the requirements of Sections 1608.3 and 1611.2.
    2. Recovering or replacing an existing roof covering shall not be required to meet the requirement for secondary (emergency overflow) drains or scuppers in Section 1502.2 for roofs that provide for positive roof drainage and meet the requirements of Sections 1608.3 and 1611.2. For the purposes of this exception, existing secondary drainage or scupper systems required in accordance with this code shall not be removed unless they are replaced by secondary drains or scuppers designed and installed in accordance with Section 1502.2.

    1512.2 Roof replacement. Roof replacement shall include the removal of all existing layers of roof assembly materials down to the roof deck.

    Exceptions:

    1. Where the existing roof assembly includes an ice barrier membrane that is adhered to the roof deck and the existing sheathing is not water-soaked or deteriorated to the point that it is not adequate as a base for additional roofing, the existing ice barrier membrane shall be permitted to remain in place and covered with an additional layer of ice barrier membrane in accordance with Section 1507 where permitted by the roof covering manufacturer and new ice barrier underlayment manufacturer.
    2. Where the existing roof includes a self-adhered underlayment and the existing sheathing is not water-soaked or deteriorated to the point that it is not adequate as a base for additional roofing, the existing self-adhered underlayment shall be permitted to remain in place and covered with an underlayment complying with Tables 1507.1.1(1), 1507.1.1(2) and 1507.1.1(3).
    3. Where the existing roof includes one layer of self-adhered underlayment and the existing layer cannot be removed without damaging the roof deck, a second layer of self-adhered underlayment is permitted to be installed over the existing self-adhered underlayment provided that the following conditions are met: 3.1. It is permitted by the roof covering manufacturer and self-adhered underlayment manufacturer. 3.2. The existing sheathing is not water-soaked or deteriorated to the point that it is not adequate as a base for additional roofing.

    15-24 2025 CALIFORNIA BUILDING CODE

Frequently asked questions

Do secondary drains have to discharge to the public storm sewer?

Not necessarily — the CPC allows secondary drains to discharge via a separate observable above‑grade outlet or to tie into the primary storm system; the designer must follow §1101.12.2.2.1 (separate) or §1101.12.2.2.2 (combined) and sizing rules for each option.

How high above the roof must the overflow inlet be?

Secondary roof drains or overflow inlets (including overflow scuppers in prescriptive residential cases) must have their inlet flow line located not less than 2 inches (51 mm) above the roof surface or low point.

Can I just add one scupper instead of a full secondary drain system?

Yes — for many configurations an open scupper or open-sided edge sized per code is an acceptable secondary method. Scuppers must be at least 4 inches high and have a width equal to the circumference of the required roof drain (or, under residential prescriptive language, be three times the size of the roof drains with 4" min height). Verify sizing with CPC Table 1103.1 and with the AHJ.

If I tie the secondary into the primary downspout, do I need bigger pipes?

Yes. The CPC requires that if the secondary is combined into the primary vertical conductor below the roof, the combined system be sized to handle double the local rainfall rate used for the primary system.

Where do I get the rainfall intensity to size the drains?

Use the local design rainfall intensity specified in the CPC (refer to Table D101.1 or other local tables referenced by CPC §1101.12.1). The CPC sets the default storm as 60 minutes, 100‑year for primary sizing unless the AHJ requires otherwise.

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