CPC · California Plumbing Code

How circuit venting works and when a relief vent is required

Q: Is a relief vent always required for four water closets?

No — the relief vent is required when four or more water closets discharge to a circuit‑vented horizontal branch and that branch connects to a drainage stack that also receives soil/waste from upper horizontal branches (§ 911.3 ) .

Q: How big must the circuit vent be?

Size per Table 703.2 using the number of circuit‑vented fixtures, but not less than 2 in (50 mm) (§ 911.2 ) .

Q: What if my layout can’t meet these prescriptive rules?

You can use an engineered vent system designed by a registered design professional and approved per the code (see § 912.1–912.2 ) .

Circuit venting lets up to eight fixtures share a horizontal drain that also acts as the vent. The circuit vent must be sized per Table 703.2 but at least 2 inches. If four or more water closets discharge to that branch and the branch ties into a stack that receives upper branch flows, a 2‑inch relief vent must be installed between the stack and the most downstream trap arm (§ **911.1**–§ **911.3**) .

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

Circuit venting lets a run of fixtures share a common vent by using the horizontal branch as a combined drain-and-vent between trap connections. The CPC permits a maximum of eight fixtures to be circuit‑vented and requires the circuit vent be sized per Table 703.2 but not less than 2 inches (50 mm) (§ 911.1, § 911.2) . A 2‑inch (50 mm) relief vent is required when a circuit‑vented horizontal branch carrying the discharge of four or more water closets ties into a drainage stack that also receives discharges from upper horizontal branches (§ 911.3) .

The most important rule: a circuit‑vented horizontal branch may serve up to eight fixtures, the circuit vent itself must be at least 2 in (50 mm) and sized per Table 703.2, and a 2 in relief vent is mandatory where four or more water closets discharge into a stack that also receives upper branch flows (§ 911.1 — § 911.3) .

Requirements in detail

Defined terms (first use bolded)

Circuit venting — using a horizontal branch as both the drain and vent for a run of fixtures between the most downstream and most upstream trap arm connections (§ 911.1) .
Relief vent — an additional vent provided to protect trap seals on circuit‑vented branches when certain loads and stack tie‑in conditions exist (§ 911.3) .
Trap arm — the piping between a trap and the horizontal branch it connects to (referenced implicitly by how trap arms connect to the circuit‑vented branch) (§ 911.1) .

Who and how many fixtures may be circuit‑vented

A maximum of eight floor‑outlet water closets, showers, bathtubs, or floor drains connected to a single horizontal branch are permitted to be circuit‑vented (§ 911.1) .
Exception: Back‑outlet and wall‑hung water closets may be circuit‑vented provided there are no floor‑outlet fixtures on the same horizontal branch; these water closets must connect horizontally to the horizontal circuit‑vented drain (§ 911.1) .

Sizing and connection rules for the circuit vent

The circuit vent size is determined using Table 703.2 based on the number of circuit‑vented fixtures but the vent shall be not less than 2 inches (50 mm) in diameter (§ 911.2) .
The circuit vent must connect to the horizontal branch on the vertical between the two most upstream trap arms (i.e., its point of connection must be between those trap arm verticals) and it shall not receive the discharge of soil or waste (§ 911.2) .
If multiple circuit vents are interconnected, each circuit vent is sized per § 911.2, and the interconnecting vent pipe is sized per Table 703.2 (§ 911.2.1) .

When a relief vent is required and how it must be installed

A 2‑inch (50 mm) relief vent is required for circuit‑vented horizontal branches that receive the discharge of four or more water closets when the horizontal branch connects to a drainage stack that receives soil/waste from upper horizontal branches (i.e., the stack has upstream discharges that could depressurize the circuit) (§ 911.3) .
The relief vent must connect to the horizontal branch between the stack and the most downstream trap arm of the circuit vent and must be installed on the vertical to the horizontal branch (§ 911.3.1) .
The relief vent is allowed to serve as a fixture drain for one‑ or two‑fixture‑unit fixtures, but those fixtures together must not exceed a total of 4 fixture units (§ 911.3.2) .

Slope and sizing of the horizontal branch (closely related)

The portion of the horizontal branch that functions as the vented section must be uniformly sloped and not more than 1 inch per foot (83.3 mm/m). The vented section must be sized for the total drainage discharge to that branch according to Table 703.2 (§ 911.4) .

Quick decision table

Decision factor	Key value / threshold	Code Reference
Maximum fixtures allowed on one circuit‑vented horizontal branch	8 fixtures	§ 911.1
Minimum circuit vent diameter	2 in (50 mm)	§ 911.2
Circuit vent sizing basis	Table 703.2 (use fixture count)	§ 911.2
Relief vent required when	4 or more water closets discharge to branch and stack receives upper branch flows	§ 911.3
Relief vent diameter	2 in (50 mm)	§ 911.3
Relief vent connection point	Between stack and most downstream trap arm of circuit	§ 911.3.1
Relief vent allowed to serve as drain	Yes — up to 4 fixture units of 1–2 FU fixtures	§ 911.3.2
Slope limit for vented horizontal branch	Not more than 1 in/ft	§ 911.4

Exceptions & special cases

Back‑outlet and wall‑hung water closets are permitted on a circuit‑vented branch only if no floor‑outlet fixtures are on that horizontal branch; they must connect horizontally (§ 911.1) .
Where multiple circuit vents are interconnected, treat each group of up to eight fixtures as a separate circuit vent for sizing and apply § 911.2 for each; the interconnecting vent pipe uses Table 703.2 sizing (§ 911.2.1) .
The relief vent may double as a small fixture drain (limited to 4 fixture units) — this is an allowance to avoid extra piping runs but must respect the fixture‑unit cap (§ 911.3.2) .

If a design departs from these prescriptive provisions, the CPC allows an engineered vent system designed by a registered design professional and approved per the code (see Chapter 912 for engineered systems) (§ 912.1–912.2) .

Common mistakes

Assuming any number of fixtures can be circuit‑vented — the limit is 8 fixtures (§ 911.1) .
Using a circuit vent smaller than 2 in (50 mm) or ignoring Table 703.2 sizing — both are required (§ 911.2) .
Forgetting the relief vent when four or more water closets feed the circuit and the branch ties into a stack that also receives upper branch flows — relief vent is mandatory (§ 911.3) .
Connecting soil/waste discharges into the circuit vent pipe itself (the code expressly prohibits the circuit vent from receiving soil or waste) (§ 911.2) .
Installing the relief vent at the wrong location — it must connect between the stack and the most downstream trap arm (§ 911.3.1) .

Worked example — step‑by‑step scenario

Scenario: A restroom group on one floor has six floor‑outlet water closets connected along one horizontal branch. That horizontal branch ties into a vertical drainage stack that also receives discharges from an upper floor.

Count fixtures intended to be circuit‑vented: 6 (≤ 8) — circuit venting is permitted (§ 911.1) .
Determine circuit vent size: consult Table 703.2 for six water closets; whichever value Table 703.2 prescribes, the vent must be at least 2 in (50 mm) (§ 911.2) . (If Table 703.2 gives 3 in for that load, use 3 in; if it gives 2 in, 2 in meets min.)
Relief vent trigger: since four or more water closets discharge to the circuit AND the branch connects to a stack that also receives upper‑branch discharges, a 2 in relief vent is required (§ 911.3) .
Relief vent location: connect the relief vent on the vertical to the horizontal branch between the stack and the most downstream trap arm of the circuit (§ 911.3.1) .
If the relief vent is to serve a small fixture drain (e.g., a mop sink), ensure that the total served does not exceed 4 fixture units (§ 911.3.2) .
Ensure the vented section of the horizontal branch is uniformly sloped (≤ 1 in/ft) and sized for the total discharge per Table 703.2 (§ 911.4) .

Related provisions

§ 911.1 — Circuit vent permitted (maximum fixtures)
§ 911.2 — Circuit vent size and connection (minimum 2 in; Table 703.2 sizing)
§ 911.3 — Relief vent required conditions, size, and connection location (2 in relief vent for ≥4 WCs into stack with upper branches)
§ 911.4 — Slope and size of horizontal branch (vented section slope ≤ 1 in/ft; sized per Table 703.2)
§ 912.0–912.2 — Engineered vent system design and minimum requirements when prescriptive rules aren’t followed (registered design professional)

Code references

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

CPC § 911.1 Medium relevance — show source text

SECTION 911—EXPLOSION CONTROL

911.1 General. Explosion control shall be provided in the following locations:

Where a structure, room or space is occupied for purposes involving explosion hazards as identified in Table 911.1.
Where quantities of hazardous materials specified in Table 911.1 exceed the maximum allowable quantities in Table 5003.1.1(1).

Such areas shall be provided with explosion (deflagration) venting, explosion (deflagration) prevention systems or barricades in accordance with this section and NFPA 68, NFPA 69 or NFPA 495 as applicable. Deflagration venting shall not be utilized as a means to protect buildings from detonation hazards.

TABLE 911.1—EXPLOSION CONTROL REQUIREMENTSf	Col2	Col3	Col4
MATERIAL	CLASS	EXPLOSION CONTROL METHODS	EXPLOSION CONTROL METHODS
MATERIAL	CLASS	Barricade construction	Explosion (deflagration) venting or explosion (deflagration) prevention systems
Hazard Category	Hazard Category	Hazard Category	Hazard Category
Combustible dustsa	—	Not required	Required
Cryogenic fluids	Flammable	Not required	Required

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FIRE PROTECTION AND LIFE SAFETY SYSTEMS

TABLE 911.1—EXPLOSION CONTROL REQUIREMENTSf—continued	Col2	Col3	Col4
MATERIAL	CLASS	EXPLOSION CONTROL METHODS	EXPLOSION CONTROL METHODS
MATERIAL	CLASS	Barricade construction	Explosion (deflagration) venting or explosion (deflagration) prevention systems
Hazard Category	Hazard Category	Hazard Category	Hazard Category
Explosives	Division 1.1	Required	Not required
Explosives	Division 1.2	Required	Not required
Explosives	Division 1.3	Not required	Required
Explosives	Division 1.4i	Not required	Required
Explosives	Division 1.5	Required	Not required
Explosives	Division 1.6	Required	Not required
Flammable gas	Gaseous	Not required	Requiredh
Flammable gas	Liquefied	Not required	Requiredh
Flammable liquids	IAb	Not required	Required
Flammable liquids	IBc	Not required	Required
Organic peroxides	Unclassified detonable	Required	Not permitted
Organic peroxides	I	Required	Not permitted
Oxidizer liquids and solids	4	Required	Not permitted
Pyrophoric	Gases	Not required	Required
Unstable (reactive)	4	Required	Not permitted
Unstable (reactive)	3 detonable	Required	Not permitted
Unstable (reactive)	3 nondetonable	Not required	Required
Water-reactive liquids and solids	3	Not required	Required
Water-reactive liquids and solids	2e	Not

CPC § 403.2.2 Medium relevance — show source text
8 High-rise 403.2.2, 403.4.8, 403.6 Hoistway door protection 3006 Hoistway enclosures 403.2.2, 713, 1023.4, 1024.3, 3002, 3007.5, 3008.5 Hoistway lighting 3007.5.2 Hoistway pressurization 909.21 Keys 3003.3 Lobby 1009.4, 1009.8, 3006, 3007.6, 3008.6

Machine rooms Table 1607.1, 3005 Means of egress 403.6, 1003.7, 1009.2.1, 1009.4, 3008

Number of elevator cars in hoistway 3002.2

Occupant evacuation elevators 403.6.2, 3008 Personnel and material hoists 3004.4

Private residence elevator 3009

Roof access 1011.12.2

Shaft enclosure 712, 3006 Signs 914, 1009.10, 3002.3, 3007.6.5, 3008.6.5 Stairway to elevator equipment 1011.12.1

Standards 3001.3 Standby power 2702.2, 3007.8, 3008.8 System monitoring 3007.7, 3008.7 Underground 405.4.3 Emergency Communications Accessible means of egress 1009.8 Alarms (see Fire Alarm and Smoke Detection Systems) Elevator 3001.2 Elevators, occupant evacuation 3008.6.6

Fire command center 403.4.6, 911, 3007.7, 3008.6.6, 3008.7 Radio coverage 403.4.5, 916 Emergency Escape and Rescue Openings 1031 Required Table 1006.3.4(1), Table 1006.3.4(2), 1031.2 Window wells 1031.5, 1031.6 Emergency Housing Appendix Q Emergency Lighting 1008.2.4, 1204.5 Emergency Power 2702 Exit signs 1013.6.3, 2702.2 Hazardous 415.11.11, 2702.2 Higher education laboratory 428.3.6, 2702.2 High-rise 403.4.8, 2702.2 Means of egress illumination 1008.2.4, 2702.2

Semiconductor fabrication 415.11.11,

2702.2 Underground buildings 405.8, 2702.2 Emergency Responders Additional exit stairway 403.5.2 Elevators 403.6, 1009.2.1, 3002.4, 3003, 3007, 3008 Fire command center 403.4.6, 911, 3007.7, 3008.6.6, 3008.7 Mall access 402.7.5 Radio coverage 403.4.5, 918 Roof access 1011.12 Safety features 914 Emittance 202
CPC § 1607.1 Medium relevance — show source text
Live load Table 1607.1

Occupant load 1004.6 Stability 1030.15 Temporary 108 Security Glazing 408.7 Security Grilles 402.8.8, 1010.3.4 Seismic 1613

Cold-formed steel 2204.2, 2206.1.1 Construction documents 107,

1603.1.5 Earthquake recording equipment Appendix L Fire resistance 704.11 Geotechnical investigation 1803.5.11, 1803.5.12 Glazing 2404 Loads 1613

Masonry 2106 Membrane structure 3102.7 Seismic design category 1613.2 Seismic detailing 1604 Site class 1613.2

Special inspection 1705.13 Statement of special inspections 1704.3.2

Steel 2202.2, 2206.2 Structural observations 1704.6.1 Structural testing 1705.14 Wood 2305, 2308.10.10, 2308.10.6,

2308.10.8 Service Sinks 11B-606, Chapter 29 Service Station (see Motor Fuel-Dispensing Facilities) Shaft Enclosure (see Vertical Opening Protection) 713 Continuity 713.11, 713.12, 713.5 Elevators 713.14

Exceptions 712.1, 1019, 1023 Exterior walls 713.6

Fire-resistance rating 707.3.1, 713.4 Group I-3 408.5 High-rise buildings 403.2.1.2, 403.2.3, 403.3.1.3, 403.5.1 Joints 713.9, 715 Materials 713.3

Opening protection 713.10, 713.8, 714, 717.5.3 Penetration 713.8

Plumbing fixtures Chapter 29 Risk category Table 1604.5 Special provisions 510.2, 510.5, 510.6 Separation 419, 420, 508.2.4, 508.3.3 Swimming pools 3109.1 Sprinkler protection 903.2.8, 903.3.2 Resistance Factor 1604 Retaining Walls 1807.2, 2304.12.2.8 Flood provisions G112.4 Seismic 1803.5.12 Reviewing Stands (see Bleachers and Grandstands) Risers, Stair (see Stairway Construction) Alternating tread devices 1011.14 Assembly 1011.5.2, 1030.10, 1030.14 Closed 1011.5.5.3

General 1011.5

CPC § 910.5 Medium relevance — show source text

910.5 Maintenance and testing. Maintenance and testing of smoke and heat vents and mechanical smoke removal systems shall be in accordance with Sections 910.5.1 and 910.5.2. A written record of inspection, testing and maintenance that includes the date, identification of personnel involved, any unsatisfactory result, corrective action taken and replaced parts shall be maintained on the premises.

910.5.1 Smoke and heat vents. Smoke and heat vents shall be maintained in an operative condition. Inspection, testing and maintenance shall be in accordance with NFPA 204 except as follows:

Mechanically operated smoke and heat vents shall be inspected annually and operationally tested not less than every 5

years. 2. Gravity dropout smoke and heat vents shall be inspected annually. 3. Fused, damaged or painted fusible links shall be replaced.

910.5.2 Mechanical smoke removal systems. Mechanical smoke removal systems shall be maintained in accordance with NFPA 204 and the equipment manufacturer’s instructions except as follows:

Systems shall be inspected and operationally tested annually.
Testing shall include the operation of all system components, controls and ancillary equipment, such as makeup air openings.
A written schedule for routine maintenance and operational testing shall be established and testing shall be conducted in accordance with the schedule.

SECTION 911—EXPLOSION CONTROL

911.1 General. Explosion control shall be provided in the following locations:

Where a structure, room or space is occupied for purposes involving explosion hazards as identified in Table 911.1.
Where quantities of hazardous materials specified in Table 911.1 exceed the maximum allowable quantities in Table 5003.1.1(1).

TABLE 911.1—EXPLOSION CONTROL REQUIREMENTSf	Col2	Col3	Col4
MATERIAL	CLASS	EXPLOSION CONTROL METHODS	EXPLOSION CONTROL METHODS
MATERIAL	CLASS	Barricade construction	Explosion (deflagration) venting or explosion (deflagration) prevention systems
Hazard Category	Hazard Category	Hazard Category	Hazard Category
Combustible dustsa	—	Not required	Required
Cryogenic fluids	Flammable	Not required	Required

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FIRE PROTECTION AND LIFE SAFETY SYSTEMS

|TABLE 911.

CPC § 115.2 Medium relevance — show source text
Evacuation 115.2, 405, 2603.3.4, 2603.3.5 Evacuation Diagrams 403.9.1.1, 403.9.2.3 Evacuation Drills 405 Frequency 405.3, Table 405.3 Notification 405.7 Recall and reentry 405.10 Evacuation Plans 404

Excess Flow Control

Defined 202

Excess Flow Valve

Defined 202

Exhausted Enclosure 202, 5003.8.5 Exhibit Gallery Occupancy load Table 1004.5 Exhibition Halls (Occupancy Group A-3)

202

Exhibits and Trade Shows 105.5.15 Existing Defined 202 Existing Buildings Chapter 11 Group I-2 1105 Outdoor occupancies 1106 Exit 1022 Configuration 1007 Defined 202

Enclosure 1023

Horizontal 1026 Number required 1006 Passageways 1024

Ramps, interior and exterior 1023, 1027 Stairways, interior or exterior 1023, 1027 Stories 1004.2.3, 1006.3, 1017.3.1 Exit Access 101, 1016, 1017, 1018, 1019 Aisles 1018

Atriums 1006.3.2, 1017.3.2, 1019.3 Balconies 1017.2.1, 1021 Common path 1006.2.1 Corridor 1020

Doors 1005.7, 1006.2, 1007, 1010,

1022.2

Intervening spaces 1016.2 Ramps 1019 Seating at tables 1030.13.1 Single exit 1006.2, 1006.3.3 Stairways 1019 Exit Discharge 202, 1023.12.1, 1023.3, 1024.4, 1028, 1029 Barriers 1023.8

Courts 1029

Horizontal exits 1028.2

Lobbies 1028.2 Public way 1028.5 Termination 1023.3

Vestibule 1028.2 Expanded Plastic Figure 3203.9(1), Figure 3203.9(2) Defined 202 Expanded Vinyl Wall or Ceiling Coverings 803.7, 803.8 Explosion Defined 202 Explosion Control 911, 2204.1, 2803.2, 2803.2.1, 2905.4, 5004.6, 5005.2.1.2, 5005.2.2.2, 5704.2.5, 5705.3.7.5.2, 5705.3.7.6.2, 5808.6, 6204.1.10, 6304.1.1,

6704.1.6 Explosive Material Chapter 56 Buildings under construction or demolition 3308

Defined 202 Explosives and Fireworks Chapter 56 Defined 202 Manufacture, assembly and testing 5605

CPC § 5705.2.6 Medium relevance — show source text

5705.2.6 Automatic container-filling operations for Class I liquids. Container-filling operations for Class I liquids involving conveyor belts or other automatic-feeding operations shall be designed to prevent static accumulations.

5705.3 Use, dispensing and mixing inside of buildings. Indoor use, dispensing and mixing of flammable and combustible liquids shall be in accordance with Section 5705.2 and Sections 5705.3.1 through 5705.3.5.3.

5705.3.1 Closure of mixing or blending vessels. Vessels used for mixing or blending of Class I liquids and Class II or III liquids heated up to or above their flash points shall be provided with self-closing, tight-fitting, noncombustible lids that will control a fire within such vessel.

Exception: Where such devices are impractical, approved automatic or manually controlled fire-extinguishing devices shall be provided.

5705.3.2 Bonding of vessels. Where differences of potential could be created, vessels containing Class I liquids or liquids handled at or above their flash points shall be electrically connected by bond wires, ground cables, piping or similar means to a static grounding system to maintain equipment at the same electrical potential to prevent sparking.

5705.3.3 Heating, lighting and cooking appliances. Heating, lighting and cooking appliances that utilize Class I liquids shall not be operated within a building or structure.

Exception: Operation in single-family dwellings.

5705.3.4 Location of processing vessels. Processing vessels shall be located with respect to distances to lot lines of adjoining property that can be built on, in accordance with Tables 5705.3.4(1) and 5705.3.4(2).

Exception: Where the exterior wall facing the adjoining lot line is a blank wall having a fire-resistance rating of not less than 4 hours, the fire code official is authorized to modify the distances. The distance shall be not less than that set forth in the Califor- nia Building Code, and where Class IA or unstable liquids are involved, explosion control shall be provided in accordance with Section 911.

TABLE 5705.3.4(1)—SEPARATION OF PROCESSING VESSELS FROM LOT LINES	Col2	Col3
PROCESSING VESSELS WITH EMERGENCY RELIEF VENTING	LOCATIONa	LOCATIONa
PROCESSING VESSELS WITH EMERGENCY RELIEF VENTING	Stable liquids	Unstable liquids
Not in excess of 2.5 psig	Table 5705.3.4(2)	2.5 times Table 5705.3.4(2)
Over 2.5 psig	1.5 times Table 5705.3.4(2)	4 times Table 5705.3.4(2)
For SI: 1 pound per square inch gauge = 6.895 kPa. a. Where protection of exposures by a public fire department or private fire brigade capable of providing cooling water streams on structures is not provided, distances shall be doubled.	For SI: 1 pound per square inch gauge = 6.895 kPa. a. Where protection of exposures by a public fire department or private fire brigade capable of providing cooling water streams on structures is not provided, distances shall be doubled.	For SI: 1 pound per square inch gauge = 6.895 kPa. a.

CPC § 1305.2.9.1 Medium relevance — show source text

For buildings equipped throughout with an automatic sprinkler system, add 2 points for activation by a sprinkler water-flow device.|a. For buildings equipped throughout with an automatic sprinkler system, add 2 points for activation by a sprinkler water-flow device.|

1305.2.9.1 Categories. The categories for fire alarm systems are:

Category a—None.
Category b—Fire alarm system with manual fire alarm boxes in accordance with Section 907.4 of the International Building Code and alarm notification appliances in accordance with Section 907.5.2 of the International Building Code .
Category c—Fire alarm system in accordance with Section 907 of the International Building Code .

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PERFORMANCE COMPLIANCE METHODS

Category d—Category c plus a required emergency voice/alarm communications system and a fire command station that conforms to Section 911 of the International Building Code and contains the emergency voice/alarm communications system controls, fire department communication system controls, and any other controls specified in Section 911 of the International Building Code where those systems are provided.

1305.2.10 Smoke control. Evaluate the ability of a natural or mechanical venting, exhaust or pressurization system to control the movement of smoke from a fire. Under the categories and occupancies in Table 1305.2.10, determine the appropriate value and enter that value into Table 1306.1 under Safety Parameter 1305.2.10, Smoke Control, for means of egress and general safety.

TABLE 1305.2.10—SMOKE CONTROL VALUES	Col2	Col3	Col4	Col5	Col6	Col7
OCCUPANCY	CATEGORIES	CATEGORIES	CATEGORIES	CATEGORIES	CATEGORIES	CATEGORIES
OCCUPANCY	a	b	c	d	e	f
A-1, A-2, A-3	0	1	2	3	6	6
A-4, E	0	0	0	1	3	5
B, M, R	0	2a	3a	3a	3a	4a
F, S	0	2a	2a	3a	3a	3a
I-2	-4	0	0	0	3	0
a. This value shall be 0 if compliance with Category d or e in Section 1305.2.8.1 has not been obtained.	a. This value shall be 0 if compliance with Category d or e in Section 1305.2.8.1 has not been obtained.	a. This value shall be 0 if compliance with Category d or e in Section 1305.2.8.1 has not been obtained.	a. This value shall be 0 if compliance with Category d or e in Section 1305.2.8.1 has not been obtained.	a. This value shall be 0 if compliance with Category d or e in Section 1305.2.8.1 has not been obtained.	a.

CPC § 1.11. Medium relevance — show source text

CHAPTER 33 – FIRE SAFETY DURING CONSTRUCTION AND DEMOLITION

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

Adopting Agency	BSC	BSC- CG	SFM	Col5	HCD	Col7	Col8	DSA	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting Agency	BSC	BSC- CG	T-24	T-19*	1	2	1/AC	AC	SS	1	1R	2	3	4	5	5	5	5	5	5	5	5	5
Adopt Entire Chapter
Adopt Entire Chapter as amended (amended sections listed below)			X
Adopt only those sections that are listed below
[California Code of Regulations, Title 19, Division 1]
Chapter / Section
3311.2			X

The California Code of Regulations (CCR), Title 19, Division 1 provisions that are found in the California Fire Code are a reprint from the current CCR, Title 19, Division 1 text for the code user’s convenience only. The scope, applicability and appeals procedures of CCR, Title 19, Division I remain the same. 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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33-2 2025 CALIFORNIA FIRE CODE

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33 FIRE SAFETY DURING CONSTRUCTION AND DEMOLITION

User notes:

About this chapter: Chapter 33 outlines general fire safety precautions for all structures and all occupancies during construction and demolition operations. In general, these requirements seek to maintain required levels of fire protection, limit fire spread, establish the appropriate operation of equipment and promote prompt response to fire emergencies. There is an emphasis on owner responsibility and the need to create and implement a site safety plan. Features regulated include fire protection systems, firefighter access to the site and building, water supply, means of egress, hazardous materials storage and use, and temporary heating equipment and other ignition sources. Fire watches are an important component of this chapter. This chapter correlates with Chapter 33 of the California Building Code .

SECTION 3301—GENERAL

CPC § 5705.3.7.5.1 Medium relevance — show source text
5705.3.7.5.1 Ventilation. Continuous mechanical ventilation shall be provided at a rate of not less than 1 cfm per square foot [0.00508 m [3] /(s × m [2] )] of floor area over the design area. Provisions shall be made for introduction of makeup air in such a manner to include all floor areas or pits where vapors can collect. Local or spot ventilation shall be provided where needed to prevent the accumulation of hazardous vapors. Ventilation system design shall comply with the California Building Code and California Mechanical Code .

Exception: Where natural ventilation can be shown to be effective for the materials used, dispensed or mixed.

5705.3.7.5.2 Explosion control. Explosion control shall be provided in accordance with Section 911.

5705.3.7.5.3 Spill control and secondary containment. Spill control shall be provided in accordance with Section 5703.4 where Class I, II or IIIA liquids are dispensed into containers exceeding a 1.3-gallon (5 L) capacity or mixed or used in open containers or systems exceeding a 5.3-gallon (20 L) capacity. Spill control and secondary containment shall be provided in accordance with Section 5703.4 where the capacity of an individual container exceeds 55 gallons (208 L) or the aggregate capacity of multiple containers or tanks exceeds 100 gallons (378.5 L).

5705.3.7.6 Closed systems. Use or mixing of flammable or combustible liquids in closed systems shall be in accordance with Sections 5705.3.7.6.1 through 5705.3.7.6.3.

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FLAMMABLE AND COMBUSTIBLE LIQUIDS

5705.3.7.6.1 Ventilation. Closed systems designed to be opened as part of normal operations shall be provided with ventilation in accordance with Section 5705.3.7.5.1.

5705.3.7.6.2 Explosion control. Explosion control shall be provided where an explosive environment can occur as a result of the mixing or use process. Explosion control shall be designed in accordance with Section 911.

Exception: Where process vessels are designed to contain fully the worst-case explosion anticipated within the vessel under process conditions considering the most likely failure.

5705.3.7.6.3 Spill control and secondary containment. Spill control shall be provided in accordance with Section 5703.4 where flammable or combustible liquids are dispensed into containers exceeding a 1.3-gallon (5 L) capacity or mixed or used in open containers or systems exceeding a 5.3-gallon (20 L) capacity. Spill control and secondary containment shall be provided in accordance with Section 5703.4 where the capacity of an individual container exceeds 55 gallons (208 L) or the aggregate capacity of multiple containers or tanks exceeds 1,000 gallons (3785 L).

5705.3.8 Use, dispensing and handling outside of buildings. Outside use, dispensing and handling shall be in accordance with Sections 5705.3.8.1 through 5705.3.8.4.

Dispensing of liquids into motor vehicle fuel tanks at motor fuel-dispensing facilities shall be in accordance with Chapter 23.
CPC § 5704.2.5 Medium relevance — show source text
Exception: Areas designated as smoking and hot work areas, and areas where hot work permits have been issued in accordance with this code.

5704.2.5 Explosion control. Explosion control shall be provided in accordance with Section 911 for indoor tanks.

5704.2.6 Separation from incompatible materials. Storage of flammable and combustible liquids shall be separated from incompatible materials in accordance with Section 5003.9.8.

Grass, weeds, combustible materials and waste Class I, II or IIIA liquids shall not be accumulated in an unsafe manner at a storage site.

5704.2.7 Design, fabrication and construction requirements for tanks. The design, fabrication and construction of tanks shall comply with NFPA 30. Each tank shall bear a permanent nameplate or marking indicating the standard used as the basis of design.

5704.2.7.1 Materials used in tank construction. The materials used in tank construction shall be in accordance with NFPA 30. The materials of construction for tanks and their appurtenances shall be compatible with the liquids to be stored.

5704.2.7.2 Pressure limitations for tanks. Tanks shall be designed for the pressures to which they will be subjected in accordance with NFPA 30.

5704.2.7.3 Tank vents for normal venting. Tank vents for normal venting shall be installed and maintained in accordance with Sections 5704.2.7.3.1 through 5704.2.7.3.5.3.

5704.2.7.3.1 Vent lines. Vent lines from tanks shall not be used for purposes other than venting unless approved.

5704.2.7.3.2 Vent-line flame arresters and pressure-vacuum vents. Listed or approved flame arresters or pressurevacuum (PV) vents that remain closed unless venting under pressure or vacuum conditions shall be installed in normal vents of tanks containing Class IB and IC liquids.

Vent-line flame arresters shall be installed in accordance with their listing or API 2000 and maintained in accordance with Section 21.8.6 of NFPA 30 or API 2000. In-line flame arresters in piping systems shall be installed and maintained in accordance with their listing or API 2028. Pressure-vacuum vents shall be installed in accordance with Section 21.4.3 of NFPA 30 or API 2000 and maintained in accordance with Section 21.8.6 of NFPA 30 or API 2000.

Exception: Where determined by the fire code official that the use of these devices can result in damage to the tank.

5704.2.7.3.3 Vent pipe outlets. Vent pipe outlets for tanks storing Class I, II or IIIA liquids shall be located such that the vapors are released at a safe point outside of buildings and not less than 12 feet (3658 mm) above the finished ground level. Vapors shall be discharged upward or horizontally away from adjacent walls to assist in vapor dispersion. Vent outlets shall be located such that flammable vapors will not be trapped by eaves or other obstructions and shall be not less than 5 feet (1524 mm) from building openings or lot lines of properties that can be built on. Vent outlets on atmospheric tanks storing Class IIIB liquids are allowed to discharge inside a building where the vent is a normally closed vent.

Exception: Vent pipe outlets on tanks storing Class IIIB liquid inside buildings and connected to fuel-burning equipment shall be located such that the vapors are released to a safe location outside of buildings.
CPC § 5004.4 Medium relevance — show source text
room.
1. The location of both the exhaust and inlet air openings shall be designed to provide air movement across all portions of the floor or room to prevent the accumulation of vapors.
2. Exhaust air shall not be recirculated to occupied areas if the materials stored are capable of emitting hazardous vapors and contaminants have not been removed. Air contaminated with explosive or flammable vapors, fumes or dusts; flammable, highly toxic or toxic gases; or radioactive materials shall not be recirculated.
5004.4 Separation of incompatible hazardous materials. Incompatible materials shall be separated in accordance with Section 5003.9.8.

5004.5 Automatic sprinkler systems. Indoor storage areas and storage buildings shall be equipped throughout with an approved automatic sprinkler system in accordance with Section 903.3.1.1. The design of the sprinkler system shall be not less than that required for Ordinary Hazard Group 2 with a minimum design area of 3,000 square feet (279 m [2] ). Where the materials or storage arrangement are required by other regulations to be provided with a higher level of sprinkler system protection, the higher level of sprinkler system protection shall be provided.

5004.6 Explosion control. Indoor storage rooms, areas and buildings shall be provided with explosion control in accordance with Section 911.

5004.7 Standby or emergency power. Where mechanical ventilation, treatment systems, temperature control, alarm, detection or other electrically operated systems are required, such systems shall be provided with an emergency or standby power in accordance with Section 1203.

For storage areas for highly toxic or toxic materials, see Sections 6004.2.2.8 and 6004.3.4.2.

5004.7.1 Exempt applications. Standby or emergency power is not required for mechanical ventilation systems for any of the following:
1. Storage of Class IB and IC flammable liquids and Class II and III combustible liquids in closed containers not exceeding a capacity of 6 [1] / 2 gallons (25 L).
2. Storage of Class 1 and 2 oxidizers.
3. Storage of Class II, III, IV and V organic peroxides.
4. Storage of asphyxiant, irritant and radioactive gases.
5004.7.2 Fail-safe engineered systems. Standby power for mechanical ventilation, treatment systems and temperature control systems shall not be required where an approved fail-safe engineered system is installed.

5004.8 Limit controls. Limit controls shall be provided in accordance with Sections 5004.8.1 and 5004.8.2.

5004.8.1 Temperature control. Materials that must be kept at temperatures other than normal ambient temperatures to prevent a hazardous reaction shall be provided with an approved means to maintain the temperature within a safe range. Redundant temperature control equipment that will operate on failure of the primary temperature control system shall be provided. Where approved, alternative means that prevent a hazardous reaction are allowed.

5004.8.2 Pressure control. Stationary tanks and equipment containing hazardous material liquids that can generate pressures exceeding design limits because of exposure fires or internal reaction shall have some form of construction or other approved means that will relieve excessive internal pressure. The means of pressure relief shall vent to an approved location or to an exhaust scrubber or treatment system where required by Chapter 60.

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HAZARDOUS MATERIALS—GENERAL PROVISIONS
CPC § 5704.2.2 Medium relevance — show source text
Tanks that have previously contained Class I liquids shall not be loaded with Class II or Class III liquids until such tanks and all piping, pumps, hoses and meters connected thereto have been completely drained and flushed.

Exception: When approved by the Enforcing Agency, the procedures prescribed in API (API-RP-2003) Recommended Practices 2003, entitled: “Protection Against Ignitions Arising Out of Static, Lightning, and Stray Currents,” may be used for changing tank

contents.

5704.2.2 Use of tank vehicles and tank cars as storage tanks. Tank cars and tank vehicles shall not be used as storage tanks.

5704.2.3 Labeling and signs. Labeling and signs for storage tanks and storage tank areas shall comply with Sections 5704.2.3.1 and 5704.2.3.2.

5704.2.3.1 Smoking and open flame. Signs shall be posted in storage areas prohibiting open flames and smoking. Signs shall comply with Section 5703.5.

5704.2.3.2 Label or placard. Tanks more than 100 gallons (379 L) in capacity, which are permanently installed or mounted and used for the storage of Class I, II or III liquids, shall bear a label and placard identifying the material therein. Placards shall be in accordance with NFPA 704.

Exceptions:
1. Tanks of 300-gallon (1136 L) capacity or less located on private property and used for heating and cooking fuels in single-family dwellings.
2. Tanks located underground.
5704.2.4 Sources of ignition. Smoking and open flames are prohibited in storage areas in accordance with Section 5003.7.

Exception: Areas designated as smoking and hot work areas, and areas where hot work permits have been issued in accordance with this code.

5704.2.5 Explosion control. Explosion control shall be provided in accordance with Section 911 for indoor tanks.

5704.2.6 Separation from incompatible materials. Storage of flammable and combustible liquids shall be separated from incompatible materials in accordance with Section 5003.9.8.

Grass, weeds, combustible materials and waste Class I, II or IIIA liquids shall not be accumulated in an unsafe manner at a storage site.

5704.2.7 Design, fabrication and construction requirements for tanks. The design, fabrication and construction of tanks shall comply with NFPA 30. Each tank shall bear a permanent nameplate or marking indicating the standard used as the basis of design.

5704.2.7.1 Materials used in tank construction. The materials used in tank construction shall be in accordance with NFPA 30. The materials of construction for tanks and their appurtenances shall be compatible with the liquids to be stored.

5704.2.7.2 Pressure limitations for tanks. Tanks shall be designed for the pressures to which they will be subjected in accordance with NFPA 30.

5704.2.7.3 Tank vents for normal venting. Tank vents for normal venting shall be installed and maintained in accordance with Sections 5704.2.7.3.1 through 5704.2.7.3.5.3.

5704.2.7.3.1 Vent lines. Vent lines from tanks shall not be used for purposes other than venting unless approved.
CPC § 910.7 High relevance — show source text
910.7 Fixtures. No water closet or urinal shall be installed on such a system. Other one, two, or three unit fixtures remotely located from the sanitary system and adjacent to a combination waste and vent system shall be permitted to be connected to such system in the conventional manner by means of waste and vent pipes of regular sizes, providing that the two pipe size increase required in Section 910.4 is based on the total fixture unit load connected to the system.

See Appendix B of this code for explanatory notes on the design of combination waste and vent systems.

911.0 Circuit Venting. 911.1 Circuit Vent Permitted. A maximum of eight flooroutlet water closets, showers, bathtubs, or floor drains con

2025 CALIFORNIA PLUMBING CODE 191

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VENTS

nected to a horizontal branch shall be permitted to be circuit vented. Each trap arm shall connect horizontally to the horizontal branch being circuit vented in accordance with Table 1002.2. The horizontal branch shall be classified as a drain and a vent from the most downstream trap arm connection to the most upstream trap arm connection to the horizontal branch.

Exception: Back-outlet and wall-hung water closets shall be permitted to be circuit vented provided that no floor-outlet fixtures are connected to the same horizontal branch. Backoutlet and wall-hung water closets shall connect horizontally to the horizontal circuit vented drain.

911.2 Circuit Vent Size and Connection. The circuit vent size shall be in accordance with Table 703.2 according to the number of circuit vented fixtures connected to the horizontal branch but shall be not less than 2 inches (50 mm) in diameter. The vent shall connect to the horizontal branch on the vertical between the two most upstream trap arms. The circuit vent pipe shall not receive the discharge of soil or

waste.

911.2.1 Multiple Circuit Vents. When multiple circuit vents are interconnected according to Section 911.4.1, each individual circuit vent shall be sized according to Section 911.2. The vent pipe connecting each circuit vent shall be sized according to Table 703.2.

911.3 Relief Vent. A 2 inch (50 mm) relief vent shall be provided for circuit-vented horizontal branches receiving the discharge of four or more water closets when connecting to a drainage stack that receives the discharge of soil or waste from upper horizontal branches.

911.3.1 Connection and Installation. The relief vent

shall connect to the horizontal branch between the stack and the most downstream trap arm of the circuit vent. The relief vent shall be installed on the vertical to the

horizontal branch.

911.3.2 Fixture Drain. The relief vent is permitted to serve as a fixture drain. Fixtures discharging to a relief vent shall be one or two fixture unit fixtures but shall not

exceed a total of 4 fixture units.

911.4 Slope and Size of Horizontal Branch. The vented section of the horizontal branch shall be uniformly sloped and not more than 1 inch per foot (83.3 mm/m). The entire length of the vented section of the horizontal branch shall be sized for the total drainage discharge to the branch according to Table 703.2.
CPC § 911.2.1 High relevance — show source text
waste.

911.2.1 Multiple Circuit Vents. When multiple circuit vents are interconnected according to Section 911.4.1, each individual circuit vent shall be sized according to Section 911.2. The vent pipe connecting each circuit vent shall be sized according to Table 703.2.

911.3 Relief Vent. A 2 inch (50 mm) relief vent shall be provided for circuit-vented horizontal branches receiving the discharge of four or more water closets when connecting to a drainage stack that receives the discharge of soil or waste from upper horizontal branches.

911.3.1 Connection and Installation. The relief vent

shall connect to the horizontal branch between the stack and the most downstream trap arm of the circuit vent. The relief vent shall be installed on the vertical to the

horizontal branch.

911.3.2 Fixture Drain. The relief vent is permitted to serve as a fixture drain. Fixtures discharging to a relief vent shall be one or two fixture unit fixtures but shall not

exceed a total of 4 fixture units.

911.4 Slope and Size of Horizontal Branch. The vented section of the horizontal branch shall be uniformly sloped and not more than 1 inch per foot (83.3 mm/m). The entire length of the vented section of the horizontal branch shall be sized for the total drainage discharge to the branch according to Table 703.2.

911.4.1 Multiple Circuit-Vented Branches. Circuitvented horizontal branches are permitted to be connected together. Each group of a maximum of eight fixtures shall be considered a separate circuit vent and shall be in accordance with Section 911.4.1.1 and Section 911.4.1.2.

911.4.1.1 Size of Parallel Horizontal

Branches. Parallel horizontal circuit vented branches shall be permitted to connect on the same floor level. Each separate circuit-vented horizontal branch that is interconnected shall be sized independently in accordance with Section 911.4.

911.4.1.2 Size of Continuous Horizontal Branches. Two or more circuit vented systems continuous on the same horizontal branch shall be uniformly sized for the total discharge into the branch.

911.5 Additional Fixtures. Fixtures, other than the circuitvented fixtures, are permitted to discharge to the horizontal branch drain. Such fixtures shall be located on the same floor as the circuit-vented fixtures and shall be either individually or common vented.

912.0 Engineered Vent System. 912.1 General. The design and sizing of a vent system shall be permitted to be determined by accepted engineering practices. The system shall be designed by a registered design professional and approved in accordance with Section 301.5. 912.2 Minimum Requirements. An engineered vent system shall provide protection of the trap seal in accordance with Section 901.3.

192 2025 CALIFORNIA PLUMBING CODE

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CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE

CHAPTER 10 - TRAPS AND INTERCEPTORS

(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.)
CPC § 908.1 High relevance — show source text
908.1 Vertical Wet Venting . . . . . . . . . . .190

908.2 Horizontal Wet Venting for a Bathroom Group . . . . . . . . . . . . . .191

909.0 Special Venting for Island Fixtures . . . . . . . . . . . . . . . . . . . . .191

909.1 General . . . . . . . . . . . . . . . . . . . . .191

910.0 Combination Waste and Vent

Systems . . . . . . . . . . . . . . . . . . . .191

910.1 Where Permitted . . . . . . . . . . . . . .191

910.2 Approval . . . . . . . . . . . . . . . . . . . .191

910.3 Vents . . . . . . . . . . . . . . . . . . . . . .191

910.4 Connections and Size . . . . . . . . .191

910.5 Vertical Waste Pipe . . . . . . . . . . .191

910.6 Cleanouts . . . . . . . . . . . . . . . . . . .191

910.7 Fixtures . . . . . . . . . . . . . . . . . . . . .191

911.0 Circuit Venting . . . . . . . . . . . . . . .191

911.1 Circuit Vent Permitted . . . . . . . . .191

911.2 Circuit Vent Size and

Connection . . . . . . . . . . . . . . . . . .192

911.3 Relief Vent . . . . . . . . . . . . . . . . . .192

911.4 Slope and Size of Horizontal Branch . . . . . . . . . . . . . . . . . . . . .192

911.5 Additional Fixtures . . . . . . . . . . . .192

912.0 Engineered Vent System . . . . . . .192

912.1 General . . . . . . . . . . . . . . . . . . . . .192

912.2 Minimum Requirements . . . . . . . .192

CHAPTER 10 TRAPS AND

INTERCEPTORS . . . . . . . . . . . . .193

1001.0 General . . . . . . . . . . . . . . . . . . . . .195

1001.1 Applicability . . . . . . . . . . . . . . . . . .195

1001.2 Where Required . . . . . . . . . . . . . .195

1002.0 Traps Protected by Vent Pipes . .195

1002.1 Vent Pipes . . . . . . . . . . . . . . . . . .195

1002.2 Fixture Traps . . . . . . . . . . . . . . . .195

1002.3 Change of Direction . . . . . . . . . . .195

1002.4 Vent Pipe Opening . . . . . . . . . . . .195

1003.0 Traps – Described . . . . . . . . . . . .195

1003.1 General Requirements . . . . . . . . .195
CPC § 905.1 Medium relevance — show source text
905.1 Grade . . . . . . . . . . . . . . . . . . . . . .190

905.2 Horizontal Drainage Pipe . . . . . . .190

905.3 Vent Pipe Rise . . . . . . . . . . . . . . .190

905.4 Roof Termination . . . . . . . . . . . . .190

905.5 Location of Opening . . . . . . . . . . .190

905.6 Common Vertical Pipe . . . . . . . . .190

906.0 Vent Termination . . . . . . . . . . . . .190

906.1 Roof Termination . . . . . . . . . . . . .190

906.2 Clearance . . . . . . . . . . . . . . . . . . .190

906.3 Use of Roof . . . . . . . . . . . . . . . . .190

906.4 Outdoor Installations . . . . . . . . . . .190

906.5 Joints . . . . . . . . . . . . . . . . . . . . . .190

906.6 Lead . . . . . . . . . . . . . . . . . . . . . . .190

906.7 Frost or Snow Closure . . . . . . . . .190

907.0 Vent Stacks and Relief Vents . . . .190

907.1 Drainage Stack . . . . . . . . . . . . . . .190

907.2 Yoke Vent . . . . . . . . . . . . . . . . . . .190

908.0 Wet Venting . . . . . . . . . . . . . . . . .190

908.1 Vertical Wet Venting . . . . . . . . . . .190

908.2 Horizontal Wet Venting for a Bathroom Group . . . . . . . . . . . . . .191

909.0 Special Venting for Island Fixtures . . . . . . . . . . . . . . . . . . . . .191

909.1 General . . . . . . . . . . . . . . . . . . . . .191

910.0 Combination Waste and Vent

Systems . . . . . . . . . . . . . . . . . . . .191

910.1 Where Permitted . . . . . . . . . . . . . .191

910.2 Approval . . . . . . . . . . . . . . . . . . . .191

910.3 Vents . . . . . . . . . . . . . . . . . . . . . .191

910.4 Connections and Size . . . . . . . . .191

910.5 Vertical Waste Pipe . . . . . . . . . . .191

910.6 Cleanouts . . . . . . . . . . . . . . . . . . .191

910.7 Fixtures . . . . . . . . . . . . . . . . . . . . .191

911.0 Circuit Venting . . . . . . . . . . . . . . .191

911.1 Circuit Vent Permitted . . . . . . . . .191

911.2 Circuit Vent Size and

Connection . . . . . . . . . . . . . . . . . .192

Frequently asked questions

When can I use circuit venting instead of individual vents?

You may use circuit venting where a horizontal branch serves up to 8 eligible fixtures and each trap arm connects horizontally to that branch; follow the sizing/connection rules in § 911.1–911.2 .

Is a relief vent always required for four water closets?

No — the relief vent is required when four or more water closets discharge to a circuit‑vented horizontal branch and that branch connects to a drainage stack that also receives soil/waste from upper horizontal branches (§ 911.3) .

How big must the circuit vent be?

Size per Table 703.2 using the number of circuit‑vented fixtures, but not less than 2 in (50 mm) (§ 911.2) .

Can the relief vent serve a fixture?

Yes — the relief vent may also act as a fixture drain for one‑ or two‑fixture‑unit fixtures provided the total does not exceed 4 fixture units (§ 911.3.2) .

What if my layout can’t meet these prescriptive rules?

You can use an engineered vent system designed by a registered design professional and approved per the code (see § 912.1–912.2) .

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Combination waste & vent, circuit vents and engineered vent systems

California Plumbing Code

How circuit venting works and when a relief vent is required

What the code requires — 2-4 sentences

Requirements in detail

Defined terms (first use bolded)

Who and how many fixtures may be circuit‑vented

Sizing and connection rules for the circuit vent

When a relief vent is required and how it must be installed

Slope and sizing of the horizontal branch (closely related)

Quick decision table

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33 FIRE SAFETY DURING CONSTRUCTION AND DEMOLITION

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