CPC · California Plumbing Code

Circuit venting — permitted configurations, sizing, and relief vent rules

Q: Can the circuit vent receive soil or waste?

No — § 911.2 explicitly states the circuit vent pipe shall not receive the discharge of soil or waste .

Q: What is the minimum size I can use for a circuit vent?

The circuit vent must be sized per Table 703.2 , but shall be not less than 2 inches (50 mm) in diameter. See § 911.2 .

Q: Are back‑outlet or wall‑hung water closets allowed on circuit vents?

They are allowed to be circuit vented only if no floor‑outlet fixtures are connected to that same horizontal branch; they must connect horizontally to the circuit‑vented drain. See § 911.1 .

Circuit venting lets up to eight listed floor‑outlet fixtures share one vented horizontal drain, but the circuit vent must be at least 2 inches and sized per Table 703.2; when the branch carries four or more water closets and ties into a stack receiving upper branches a 2‑inch relief vent (installed vertically between the stack and the most downstream trap arm) is required.

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Last reviewed: July 6, 2026

What the code requires — plain English

Circuit venting permits a group of fixtures on a single horizontal branch to be vented together rather than individually, but the number of circuit‑vented fixtures and how the vents are sized and located are tightly limited. The key limits are a maximum of eight circuit‑vented floor‑outlet fixtures and a minimum circuit vent diameter of 2 inches (sized according to Table 703.2); a 2‑inch relief vent is required for certain stacks when the branch carries four or more water closets. See § 911.1, § 911.2, and § 911.3 for the controlling requirements.

The most important rule: a horizontal branch may be circuit‑vented only for up to eight floor‑outlet fixtures; the circuit vent must be sized per Table 703.2 but not less than 2 in., and a 2‑in. relief vent is required where four or more water‑closets discharge to the branch and that branch ties into a stack receiving upper horizontal branches.

Requirements in detail

Which fixtures may be circuit vented

A horizontal branch may be circuit‑vented for a maximum of eight floor‑outlet water closets, showers, bathtubs, or floor drains connected to that branch (counting all circuit‑vented fixtures together). See § 911.1.
Exception: Back‑outlet and wall‑hung water closets may be circuit vented only if no floor‑outlet fixtures are on the same horizontal branch; they must connect horizontally to the branch. See § 911.1.

Sizing and where to connect the circuit vent

The circuit vent sizing is determined by Table 703.2 but the vent shall be not less than 2 inches (50 mm) diameter. The vent must connect to the horizontal branch on the vertical between the two most upstream trap arms. The circuit vent must not receive soil or waste discharge. See § 911.2.
When multiple circuit vents are interconnected, each circuit vent is sized per § 911.2 and the connecting vent pipe is sized per Table 703.2. See § 911.2.1.

Relief vent rules

A 2‑inch (50 mm) relief vent is required for circuit‑vented horizontal branches that discharge four or more water closets when that branch connects to a drainage stack that receives discharge from upper horizontal branches. See § 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 it must be installed on the vertical to the horizontal branch (i.e., vertical connection from the branch). See § 911.3.1.
The relief vent is permitted to serve as a fixture drain, but fixtures discharging to it must be one‑ or two‑fixture‑unit fixtures and the total shall not exceed 4 fixture units. See § 911.3.2.

Horizontal branch slope and sizing

The vented section of the horizontal branch must be uniformly sloped and not more than 1 inch per foot (83.3 mm/m). The entire vented length must be sized for the total drainage discharge to the branch using Table 703.2. See § 911.4.
Circuit‑vented horizontal branches may be connected together; rules for sizing depend on whether branches are parallel (each sized independently) or continuous (uniform sizing for total discharge). See § 911.4.1, § 911.4.1.1, § 911.4.1.2.

Quick decision table (code references included)

Parameter / decision point	Value or action	When / where	Code reference
Maximum circuit‑vented fixtures on a horizontal branch	8 fixtures	Floor‑outlet WCs, showers, bathtubs, floor drains	§ 911.1
Minimum circuit vent diameter	2 in. (50 mm) (or per Table 703.2)	Circuit vent sizing — never less than 2 in.	§ 911.2
Relief vent required	2 in. relief vent when ≥4 water closets on branch and branch ties into stack receiving upper horizontal branches	Relief vent mandatory in this configuration	§ 911.3
Relief vent connection location	Connect between stack and most downstream trap arm; vertical to horizontal	Installation rule, relief vent placement	§ 911.3.1
Relief vent serving fixtures	May serve as fixture drain up to 4 fixture units (fixtures must be 1‑ or 2‑fu)	Limit when using relief vent as drain	§ 911.3.2
Slope of vented horizontal branch	≤ 1 in./ft	Vented section uniform slope requirement	§ 911.4
Sizing of horizontal branch and connecting vents	Size for total discharge per Table 703.2	Entire vented section and connections	§ 911.4 and § 911.2.1

Exceptions & special cases

Back‑outlet and wall‑hung water closets are allowed on a circuit‑vented branch only if no floor‑outlet fixtures are connected to that same horizontal branch; they must still connect horizontally. See § 911.1.
When multiple circuit vents are interconnected per § 911.4.1, treat each group of up to eight fixtures as a separate circuit vent for sizing; the interconnecting vent piping follows Table 703.2. See § 911.2.1 and § 911.4.1.
If an engineered vent system is used (non‑prescriptive method), it must be designed by a registered design professional and approved per § 912.1 (engineered vent systems are allowed in lieu of the prescriptive circuit vent rules). See § 912.1.

Common mistakes

Counting the wrong fixtures: designers often forget that the limit of eight applies to the group of floor‑outlet fixtures specifically listed in § 911.1; adding other types or misclassifying fixtures can invalidate a circuit vent.
Using a circuit vent smaller than 2 in.: even if Table 703.2 might suggest a smaller size for the number of fixture units, the circuit vent may not be less than 2 in. per § 911.2.
Forgetting the relief vent trigger: a 2‑inch relief vent is required only when the circuit branch has four or more water closets and ties into a stack that receives flow from upper horizontals — it is not automatically required for every circuit vent. Misapplying this causes unnecessary piping or noncompliance. See § 911.3.
Relief vent connection errors: the relief vent must be located between the stack and the most downstream trap arm of the circuit vent and installed on the vertical to the horizontal branch; common practice mistakes are lateral connections in the wrong location. See § 911.3.1.
Using the relief vent as a fixture drain without checking fixture unit limits: the relief vent may carry fixtures only if they total ≤ 4 fixture units and are 1‑ or 2‑fu each (per § 911.3.2).

Worked example — step‑by‑step application

Scenario: A single horizontal branch on one floor will serve 6 floor‑outlet water closets and 2 showers (all connect horizontally to the branch). That horizontal branch then connects to a drainage stack which also receives upper floor branches.

Steps:

Count circuit‑vented fixtures: 6 WCs + 2 showers = 8 fixtures. Because this is ≤ 8, circuit venting is permitted. See § 911.1.
Circuit vent sizing: look up total fixture units and the developed length, then size per Table 703.2, but ensure the circuit vent is not less than 2 in. (minimum). If Table 703.2 gives ≥2 in., use that size; otherwise use 2 in. See § 911.2.
Relief vent check: because the branch discharges six water closets (which is ≥ 4), and the branch ties into a stack that receives upper horizontal branches, a 2‑inch relief vent is required. Install the relief vent between the stack and the most downstream trap arm and place it on the vertical to the horizontal branch. See § 911.3 and § 911.3.1.
Relief vent used as fixture drain? If you intend to have fixtures discharge to the relief vent, ensure they are one‑ or two‑fixture‑unit fixtures and total no more than 4 fixture units. See § 911.3.2.
Slope and sizing of horizontal branch: the vented section must be uniformly sloped ≤ 1 in./ft, and the horizontal branch must be sized for the total discharge using Table 703.2. See § 911.4.

If at any step the sizing from Table 703.2 or other site constraints cannot be met, consider an engineered vent system per § 912.0 and have a registered design professional provide the engineered design.

Related provisions (quick list)

§ 911.1 — Circuit vent permitted (maximum fixtures; horizontal‑connection rule).
§ 911.2 — Circuit vent size and connection (minimum 2 in.; Table 703.2).
§ 911.2.1 — Multiple circuit vents interconnection sizing.
§ 911.3 — Relief vent required (2 in.; when ≥4 WCs and stack receives upper branches).
§ 911.3.1 — Relief vent connection and installation location.
§ 911.3.2 — Relief vent serving as fixture drain (fixture unit limits).
§ 911.4 — Slope and size of the vented horizontal branch (≤1 in./ft; size for total discharge).
§ 911.4.1 / § 911.4.1.1 / § 911.4.1.2 — Multiple circuit‑vented branch interconnection rules and sizing approaches.
Table 703.2 — Sizing reference for vents and drains (used repeatedly in §§ 911.2, 911.2.1, 911.4).
§ 1002.2 — Requirements for trap arms to connect horizontally (referenced by § 911.1).

Code references

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

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

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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 § 0.249 High relevance — show source text

24
|0.249
|0.048
|–
| |4.94|0.326|0.063|–| |5.65|0.413|0.080|–| |6.36|0.507|0.098|–| |7.06|0.611|0.118|0.030| |7.77|0.723|0.139|0.035| |8.47|0.843|0.162|0.041| |9.18|0.969|0.187|0.047| |9.89|1.108|0.212|0.053| |10.59|1.252|0.240|0.060| |12.36|1.647|0.315|0.079| |14.12
|2.090
|0.398
|0.100
| |15.89
|2.580
|0.490
|0.123
| |17.66|3.116|0.591|0.148| |19.42|–|0.701|0.176| |21.19|–|0.818|0.205| |22.95|–|0.944|0.236| |24.72|–|1.078|0.268| |28.25|–|1.369|0.341| |31.78|–|1.690|0.421| |35.31|–|2.043|0.509| |38.84|–|2.425|0.603| |42.37|–|2.838|0.705| |45.90
|–
|3.280
|0.814
| |49.43|–|3.751|0.929| |52.97|–|4.249|1.052| |56.50|–|–|1.181| |60.03|–|–|1.318| |63.56|–|–|1.461| |67.09|–|–|1.611| |70.62|–|–|1.768| |81.21|–|–|2.276| |88.28|–|–|2.647| |95.34|–|–|3.044|

FLOW RATE (SCFM)1	PRESSURE DROP (psi) PER 100 FEET2	Col3	Col4
FLOW RATE (SCFM)1	1⁄2 INCH PIPE	3⁄4 INCH PIPE	1 INCH PIPE
5.30	0.126	0.024	–
10.59	0.430	0.082	–
15.89	0.886	0.168	–
21.19	1.485	0.281	–
26.48	2.220	0.419	–
31.78	3.089	0.581	–
37.08	4.087	0.766	–
42.37	–	0.975	–
47.67	–	1.206	–
52.97	–	1.460	0.361
58.26	–	1.736	0.429
63.56	–	2.033	0.502
68.85	–	2.

CPC § 60532-3696. High relevance — show source text
SAE Society of Automotive Engineers, 400 Commonwealth Drive, Warrendale, PA 15096.

TCNA Tile Council of North America, Inc. 100 Clemson Research Blvd., Anderson, SC 29625.

UL Underwriters Laboratories, Inc., 333 Pfingsten Road, Northbrook, IL 60062.

WQA Water Quality Association, 4151 Naperville Road, Lisle, IL 60532-3696.

WSC Water Systems Council, 1101 30th Street, NW, Suite 500, Washington, D.C. 20007.

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APPENDICES

The appendices are intended to supplement the provisions of the installation requirements of this code. The definitions in Chapter 2 are also applicable to the appendices.

TABLE OF CONTENTS

Page Appendix A Recommended Rules for Sizing the Water Supply System...........................................................................365

Appendix B Explanatory Notes on Combination Waste and Vent Systems ......................................................................381

Appendix C Alternate Plumbing Systems..........................................................................................................................385

Appendix D Sizing Storm Water Drainage Systems..........................................................................................................395

Appendix E Manufactured/Mobile Home Parks and Recreational Vehicle Parks .............................................................405

Appendix F Firefighter Breathing Air Replenishment Systems .........................................................................................417

Appendix G Sizing of Venting Systems ............................................................................................................................423

Appendix H Private Sewage Disposal Systems ................................................................................................................435

Appendix I Installation Standards ....................................................................................................................................447

Appendix J Combination of Indoor and Outdoor Combustion and Ventilation Opening Design.......................................487

Appendix K Potable Rainwater Catchment Systems ........................................................................................................491

Appendix L Sustainable Practices ....................................................................................................................................497

Appendix M Peak Water Demand Calculator ....................................................................................................................517

Appendix N Impact of Water Temperature on the Potential for Scalding and Legionella Growth .....................................525

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TABLE OF CONTENTS (continued)

Appendix O Non-Sewered Sanitation Systems .................................................................................................................531

Appendix P

Professional Qualifications.............................................................................................................................535

Appendix Q

Indoor Horticultural Facilities..........................................................................................................................539

Appendix R Tiny Houses...............................................................................
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.

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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 § 905.5 High relevance — show source text
905.5 Location of Opening. The vent pipe opening from soil or waste pipe shall not be below the weir of the trap.

Exception: Water closets and similar fixtures. 905.6 Common Vertical Pipe. Two fixtures shall be permitted to be served by a common vertical pipe where each such fixture wastes separately into an approved double fitting having inlet openings at the same level.

906.0 Vent Termination.

906.1 Roof Termination. Each vent pipe or stack shall extend through its flashing and shall terminate vertically not less than 6 inches (152 mm) above the roof nor less than 1 foot (305 mm) from a vertical surface. ABS and PVC piping exposed to sunlight shall be protected by water based synthetic latex paints.

906.2 Clearance. Each vent shall terminate not less than 10 feet (3048 mm) from, or not less than 3 feet (914 mm) above, an openable window, door, opening, air intake, or vent shaft, or not less than 3 feet (914 mm) in every direction from a lot line, alley and street excepted. 906.2.1 [OSHPD 1,1R, 2, 3, 4 & 5] Each vent pipe shall terminate not less than twenty-five (25) feet (7620 mm) from any air intake or vent shaft. 906.3 Use of Roof. Vent pipes shall be extended separately or combined, of full required size, not less than 6 inches (152 mm) above the roof or firewall. Flagpoling of vents shall be prohibited except where the roof is used for assembly purposes or parking. Vents within 10 feet (3048 mm) of a part of the roof that is used for assembly purposes or parking shall extend not less than 7 feet (2134 mm) above such roof and shall securely stay. 906.4 Outdoor Installations. Vent pipes for outdoor installations shall extend not less than 10 feet (3048 mm) above the surrounding ground and shall be securely supported.

906.5 Joints. Joints at the roof around vent pipes shall be made watertight by the use of approved flashings or flashing material.

906.6 Lead. (See Chapter 17) Sheet lead shall comply with the following:

(1) For safe pans – not less than 4 pounds per square foot (lb/ft [2] ) (19 kg/m [2] ) or [1] ⁄ 16 of an inch (1.6 mm) thick. (2) For flashings or vent terminals – not less than 3 lb/ft [2] (15 kg/m [2] ) or 0.0472 of an inch (1.2 mm) thick. (3) Lead bends and lead traps shall be not less than [1] ⁄ 8 of an inch (3.2 mm) in wall thickness.

906.7 Frost or Snow Closure. Where frost or snow closure is likely to occur in locations having minimum design temperature below 0°F (-17.8°C), vent terminals shall be not less than 3 inches (76 mm) in diameter, but in no event smaller than the required vent pipe. The change in diameter shall be made inside the building not less than 1 foot (305 mm) below the roof in an insulated space and terminate not less than 10 inches (254 mm) above the roof, or in accordance with the Authority Having Jurisdiction.

907.0 Vent Stacks and Relief Vents.

CPC § 0.099 High relevance — show source text

c, d, e	Col2	Col3	Col4	Col5	Col6
MAXIMUM DESIGN PRESSURE (+ or - psf)	MINIMUM PANEL SPAN RATING	MINIMUM PANEL PERFORMANCE CATEGORY	NAIL TYPE AND SIZE	FASTENERa SPACINGe ALONG EDGES AND INTERMEDIATE SUPPORTS (inches)	FASTENERa SPACINGe ALONG EDGES AND INTERMEDIATE SUPPORTS (inches)
MAXIMUM DESIGN PRESSURE (+ or - psf)	MINIMUM PANEL SPAN RATING	MINIMUM PANEL PERFORMANCE CATEGORY	NAIL TYPE AND SIZE	Galvanized Steel	Stainless Steel
30	24/0	3/8	6d box (2 × 0.099 × 0.266 head diameter)	6f	4
40	24/0	3/8	6d box (2 × 0.099 × 0.266 head diameter)	6	4
50	24/0	3/8	6d box (2 × 0.099 × 0.266 head diameter)	4	4
50	24/0	3/8	8d common (21/2 × 0.131 × 0.281 head diameter)	6	6
60	24/0	3/8	6d box (2 × 0.099 × 0.266 head diameter)	4	3
60	24/0	3/8	8d common (21/2 × 0.131 × 0.281 head diameter)	6	4
70	24/16	7/16	8d common (21/2× 0.131 × 0.281 head diameter)	4	4
70	24/16	7/16	10d box (3 × 0.128 × 0.312 head diameter)	6	4
80	24/16	7/16	8d common (21/2 × 0.131 × 0.281 head diameter)	4	4
80	24/16	7/16	10d box (3 × 0.128 × 0.312 head diameter)	6	4
90	32/16	15/32	8d common (21/2 × 0.131 × 0.281 head diameter)	4	3
90	32/16	15/32	10d box (3 × 0.128 × 0.312 head diameter)	6	4
For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa. a. Fasteners shall comply with Sections R703.3.2 and R703.3.3. b. Maximum spacing of exterior soffit framing members shall not exceed 24 inches. c. Wood structural panels shall be of an exterior exposure grade. d. Wood structural panels shall be installed with strength axis perpendicular to supports with not fewer than two continuous spans. e.

CPC § 3.2.2 High relevance — show source text

1810 A .3.2.2 Prestressing steel. Prestressing steel shall conform to ASTM A416.

1810 A .3.2.3 Steel. Structural steel H-piles and structural steel sheet piling shall conform to the material requirements in ASTM A6. Steel pipe piles shall conform to the material requirements in ASTM A252. Fully welded steel piles shall be fabricated from plates that conform to the material requirements in ASTM A36, ASTM A283, ASTM A572, ASTM A588 or ASTM A690.

1810 A .3.2.4 Timber. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.

1810 A .3.2.5 Protection of materials. Where boring records or site conditions indicate possible deleterious action on the materials used in deep foundation elements because of soil constituents, changing water levels or other factors, the elements shall be adequately protected by materials, methods or processes approved by the building official. Protective materials shall be applied to the elements so as not to be rendered ineffective by installation. The effectiveness of such protective measures for the particular purpose shall have been thoroughly established by satisfactory service records or other evidence.

1810 A .3.2.6 Allowable stresses. The allowable stresses for materials used in deep foundation elements shall not exceed those specified in Table 1810 A .3.2.6.

TABLE 1810A.3.2.6—ALLOWABLE STRESSES FOR MATERIALS USED IN DEEP FOUNDATION ELEMENTS	Col2
MATERIAL TYPE AND CONDITION	MAXIMUM ALLOWABLE STRESSa
1. Concrete or grout in compressionb Cast-in-place with a permanent casing in accordance with Section 1810_A_.3.2.7 or Section 1810_A_.3.5.3.4 Cast-in-place in other permanent casing or rock Cast-in-place without a permanent casing Precast nonprestressed Precast prestressed	0.4_f ′c_ 0.33_f ′c_ 0.3_f ′c_ 0.33_f ′c_ 0.33_f ′c_ - 0.27_fpc_
2. Nonprestressed reinforcement in compression	0.4_fy_ ≤ 30,000 psi
3. Steel in compression Cores within concrete-filled pipes or tubes Pipes, tubes or H-piles, where justified in accordance with Section 1810.3.2.8 Pipes or tubes for micropiles Other pipes, tubes or H-piles Helical piles	0.5_Fy_ ≤ 32,000 psi 0.5_Fy ≤ 32,000 psi 0.4_Fy ≤ 32,000 psi 0.35_Fy_ ≤ 24,000 psi 0.6_Fy_ ≤ 0.5_Fu_
4. Nonprestressed reinforcement in tension Within micropiles Other conditions For load combinations that do not include wind or seismic loads For load combinations that include wind or seismic loads	0.6_fy_ 0.5_fy_ ≤ 30,000 psi 0.5_fy_ ≤ 40,000 psi
5.

CPC § 25.4 High relevance — show source text
explosion hazards existd|Detonation|Required|Not permitted| |Where explosion hazards existd|Deflagration|Not required|Required| |For SI: 1 inch per second = 25.4 mm/s.
a. Combustible dusts where manufactured, generated or used in such a manner that the concentration and conditions create a fire or explosion hazard
based on information prepared in accordance with Section 104.2.2. See definition of “Combustible dust” in Chapter 2.
b. Storage or use.
c. In open use or dispensing.
d. Rooms containing dispensing and use of hazardous materials where an explosive environment can occur because of the characteristics or nature of the
hazardous materials or as a result of the dispensing or use process.
e. A method of explosion control shall be provided where Class 2 water-reactive materials can form potentially explosive mixtures.
f. Explosion venting is not required for Group H-5 Fabrication Areas complying with Chapter 27 and the_California Building Code_.
g. Where explosion control is required in Section 1207.6.3.
h. Not required for Category 1B Flammable Gases having a burning velocity not exceeding 3.9 inches per second.
i. Does not apply to consumer fireworks, 1.4G.|For SI: 1 inch per second = 25.4 mm/s.
a. Combustible dusts where manufactured, generated or used in such a manner that the concentration and conditions create a fire or explosion hazard
based on information prepared in accordance with Section 104.2.2. See definition of “Combustible dust” in Chapter 2.
b. Storage or use.
c. In open use or dispensing.
d. Rooms containing dispensing and use of hazardous materials where an explosive environment can occur because of the characteristics or nature of the
hazardous materials or as a result of the dispensing or use process.
e. A method of explosion control shall be provided where Class 2 water-reactive materials can form potentially explosive mixtures.
f. Explosion venting is not required for Group H-5 Fabrication Areas complying with Chapter 27 and the_California Building Code_.
g. Where explosion control is required in Section 1207.6.3.
h. Not required for Category 1B Flammable Gases having a burning velocity not exceeding 3.9 inches per second.
i. Does not apply to consumer fireworks, 1.4G.|For SI: 1 inch per second = 25.4 mm/s.
a. Combustible dusts where manufactured, generated or used in such a manner that the concentration and conditions create a fire or explosion hazard
based on information prepared in accordance with Section 104.2.2. See definition of “Combustible dust” in Chapter 2.
b. Storage or use.
c. In open use or dispensing.
d. Rooms containing dispensing and use of hazardous materials where an explosive environment can occur because of the characteristics or nature of the
hazardous materials or as a result of the dispensing or use process.
e. A method of explosion control shall be provided where Class 2 water-reactive materials can form potentially explosive mixtures.
f. Explosion venting is not required for Group H-5 Fabrication Areas complying with Chapter 27 and the_California Building Code_.
g. Where explosion control is required in Section 1207.6.3.
h.

CPC § 911.1 High 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

2025 CALIFORNIA FIRE CODE 9-67

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

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 § 910.0 High relevance — show source text
910.0 Combination Waste and Vent Systems. 910.1 Where Permitted. Combination waste and vent systems shall be permitted where structural conditions preclude the installation of conventional systems as otherwise prescribed by this code. 910.2 Approval. Construction documents for each combination waste and vent system shall first be approved by the Authority Having Jurisdiction before a portion of such system is installed.

910.3 Vents. Each combination waste and vent system, as defined in Chapter 2, shall be provided with a vent or vents adequate to ensure free circulation of air. A branch exceeding 15 feet (4572 mm) in length shall be separately vented in an approved manner. The area of a vent installed in a combination waste and vent system shall be not less than one-half the inside cross-sectional area of the drainpipe served. The vent connection shall be downstream of the uppermost fixture. 910.4 Connections and Size. Branches serving traps shall connect to the main line at an angle not exceeding 2 percent. Each waste pipe and each trap in such a system shall be not less than two pipe sizes exceeding the sizes required by Chapter 7 of this code, and not less than two pipe sizes exceeding a fixture tailpiece or connection. 910.5 Vertical Waste Pipe. No vertical waste pipe shall be used in such a system, except the tailpiece or connection between the outlet of a plumbing fixture and the trap. Such tailpieces or connections shall be as short as possible, and in no case shall exceed 2 feet (610 mm).

Exception: Branch lines shall be permitted to have 45 degree (0.79 rad) vertical offsets.

910.6 Cleanouts. An accessible cleanout shall be installed in each vent for the combination waste and vent system. Cleanouts shall not be required on a wet-vented branch serving a single trap where the fixture tailpiece or connection is not less than 2 inches (50 mm) in diameter and provides ready access for cleaning through the trap.

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

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

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.
CPC § 0.197 High relevance — show source text
)|0.197 (12 ga.)|0.097 (12 ga.)| |12 to 15|24|0.055 (16 ga.)|0.055 (16 ga.)|0.055 (16 ga.)|0.055 (16 ga.)|0.068 (14 ga.)|0.068 (14 ga.)|0.097 (12 ga.)|0.097 (12 ga.)|0.097 (12 ga.)| |16 to 20|0|0.055 (16 ga.)|0.055 (16 ga.)|0.068 (14 ga.)|0.097 (12 ga.)|0.112 (11 ga.)|––|––|––|––| |16 to 20|96|0.055 (16 ga.)|0.055 (16 ga.)|0.055 (16 ga.)|0.055 (16 ga.)|0.068 (14 ga.)|0.068 (14 ga.)|0.112 (11 ga.)|0.112 (11 ga.)|0.112 (11 ga.)| |16 to 20|48|0.055 (16 ga.)|0.055 (16 ga.)|0.055 (16 ga.)|0.055 (16 ga.)|0.068 (14 ga.)|0.068 (14 ga.)|0.097 (12 ga.)|0.097 (12 ga.)|0.097 (12 ga.)| |16 to 20|24|0.055 (16 ga.)|0.055 (16 ga.)|0.055 (16 ga.)|0.055 (16 ga.)|0.068 (14 ga.)|0.068 (14 ga.)|0.097 (12 ga.)|0.097 (12 ga.)|0.097 (12 ga.)|

For SI units: 1 inch = 25.4 mm, 1 inch water column = 0.249 kPa

Aluminum ducts shall not be used in systems conveying flammable vapors, fumes, or explosive dusts, nor in Class 2, 3, or 4 systems. Galvanized steel and aluminum ducts shall not be used where the temperature of the material being conveyed exceeds 400°F (204°C). Metal ducts used in Class 5 systems that are not resistant to the corrosiveness of the product shall be protected with an approved corrosion-resistant material. 506.2 Construction. Ducts used for conveying products shall be airtight construction as approved by the Authority Having Jurisdiction, and shall not have openings other than those required for operation and maintenance of the system. Ducts constructed of steel shall comply with Table 506.2(1) or Table 506.2(2). Exceptions: (1) Class 1 product-conveying ducts that operate at less than 4 inches water column (0.9 kPa) negative pressure and con

vey noncorrosive, nonflammable and nonexplosive materials at temperatures not exceeding 250°F (121°C) shall be permitted to be constructed in accordance with SMACNA HVAC Duct Construction Standards–Metal and Flexible.
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

Frequently asked questions

When exactly does the relief‑vent rule (2‑inch) apply?

The relief vent is required when the circuit‑vented horizontal branch carries the discharge of four or more water closets and that branch connects to a drainage stack that receives soil/waste from upper horizontal branches; the relief vent must be 2 in. per § 911.3.

Can the circuit vent receive soil or waste?

No — § 911.2 explicitly states the circuit vent pipe shall not receive the discharge of soil or waste.

What is the minimum size I can use for a circuit vent?

The circuit vent must be sized per Table 703.2, but shall be not less than 2 inches (50 mm) in diameter. See § 911.2.

Can the relief vent also act as a fixture drain?

Yes, the relief vent is permitted to serve as a fixture drain, but only for 1‑ or 2‑fixture‑unit fixtures and not to exceed a total of 4 fixture units. See § 911.3.2.

Are back‑outlet or wall‑hung water closets allowed on circuit vents?

They are allowed to be circuit vented only if no floor‑outlet fixtures are connected to that same horizontal branch; they must connect horizontally to the circuit‑vented drain. See § 911.1.

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Related in the CPC

When are combination waste-and-vent systems permitted and how are they sized?

Vent types, vent sizing, and maximum lengths/unit loading for vents

Venting, combination waste-and-vent, and special venting methods

California Plumbing Code