CPC · California Plumbing Code

What must an engineered vent system include (minimum engineered requirements)?

If you choose to design venting by engineering methods, the CPC requires a licensed design professional to prepare and submit the engineered vent design for approval, and the system must protect trap seals so the outlet-side pressure differential never exceeds 1 inch water column.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

An engineered vent system may be sized and detailed by engineering methods rather than the prescriptive tables, but it must be designed by a registered design professional and be approved by the authority having jurisdiction in accordance with § 301.5. The minimum performance requirement is that the system provide protection of the trap seal — i.e., it must prevent excessive pressure differential on the trap outlet — as required by § 901.3. These prescriptions are stated in § 912.1 and § 912.2 of the California Plumbing Code.

The single most important rule: an engineered vent system must be designed and stamped by a registered design professional and must ensure that trap seals are not exposed to more than 1 inch water column pressure differential on the outlet side of the trap.

Requirements in detail

1) Who must design it

The system shall be designed by a registered design professional (architect or engineer) — this is mandatory for any engineered vent system under § 912.1.

2) How it may be sized and documented

Sizing and design may be determined by accepted engineering practices (hydraulic analysis, CFD or other recognized methods) rather than only by prescriptive tables, per § 912.1. The design must be submitted and approved per the permit/approval process (see § 301.5 reference in the same clause).

3) Minimum performance (what it must accomplish)

The engineered vent system must provide trap-seal protection in accordance with § 901.3 — explicitly the venting must prevent a trap from experiencing a pressure differential that exceeds 1 inch water column (0.24 kPa) on the outlet side of the trap.

4) Submission & approval

The design documents must be prepared, signed and sealed by the registered design professional and approved in accordance with the administrative approval process cited in § 301.5 (the CPC text references approval per § 301.5 in § 912.1). If the exact submission requirements of § 301.5 are needed, consult § 301.5 directly because the short 912 text references it without restating all details.

Decision-relevant summary table

Element	Minimum / required value	Responsible party	Code Reference
Designer	Registered design professional (signed & sealed documents)	RDP	§ 912.1
Design method	Accepted engineering practices (engineered analysis permitted)	RDP	§ 912.1
Approval	Submit for approval per administrative permit process	Applicant / AHJ	§ 912.1 (references § 301.5)
Minimum performance	Protect trap seal so outlet-side pressure differential ≤ 1 inch water column (0.24 kPa)	RDP / Installer	§ 912.2 referencing § 901.3
Materials & fittings	Use code-listed materials for vents (per Chapter 9 tables)	RDP / Installer	See § 903.1 and Table 701.2 for materials

Exceptions & special cases

The CPC text for § 912.0–912.2 is concise: it permits engineered design but does not relax the minimum trap-seal protection requirement; engineered systems must still meet § 901.3.
The code references the approval path (§ 301.5) for engineered systems; if a local authority requires additional submittal items, follow that AHJ’s interpretation — the 912 text does not enumerate permit submittals itself.
If your engineered vent is an alternative to a prescriptive vent, expect the AHJ to require calculations, drawings, and possibly verification/testing (the CPC provides alternate/engineered design procedures elsewhere; see administrative sections and Appendix C for guidance).

Common mistakes

Assuming “engineered” means no review: you still must obtain approval per § 301.5; the design must be signed/sealed by an RDP (§ 912.1).
Ignoring the trap-seal performance requirement: the engineered design must still limit trap outlet pressure differential to ≤ 1 inch water column per § 901.3 (referenced by § 912.2). Omitting this can cause rejection.
Not documenting calculation methods: because sizing is by “accepted engineering practices,” include method description, assumptions, boundary conditions, and worst-case scenarios in the submittal. The CPC text allows engineering methods but the AHJ will require justification.
Using materials or installations that conflict with Chapter 9 material limits (for example underground galvanized steel is restricted) — check § 903.1 and Table 701.2.

Worked example — concrete scenario applying the rule with numbers

Scenario: An RDP is designing an engineered vent system for a commercial restroom cluster where a hydraulic analysis predicts transient blowback events. The RDP analyzes worst-case pneumatic transients and predicts a maximum outlet-side pressure differential at a particular trap of 0.8 inch water column under design load.

Step 1 — Responsibility: The RDP prepares and signs sealed plans, per § 912.1, and submits them for approval per § 301.5.
Step 2 — Check minimum: Compare predicted trap pressure differential (0.8 in. WC) to the code limit of 1.0 in. WC from § 901.3 (required by § 912.2). Because 0.8 in. WC < 1.0 in. WC, the design meets the CPC minimum trap-seal protection requirement.
Step 3 — Documentation: The RDP includes the calculation method, boundary conditions, and an explanation that worst-case transient pressure is below the 1 in. WC threshold, and submits this as part of the engineered-design package for AHJ review.

If the analysis had predicted 1.2 in. WC, the RDP must revise the vent arrangement (add vent capacity, change geometry, add relief vents or trap seal primers, etc.) so the predicted maximum is ≤ 1.0 in. WC, then resubmit for approval. The CPC does not prescribe exactly how to achieve this for engineered systems — it requires the performance be met and the design to be prepared by an RDP.

Related provisions

§ 912.1 — Engineered vent system: design by registered design professional; approval per § 301.5.
§ 912.2 — Minimum requirements: protection of the trap seal in accordance with § 901.3.
§ 901.3 — Trap Seal Protection: vent system must prevent trap outlet pressure differential greater than 1 inch water column (0.24 kPa).
§ 301.5 — (Referenced by § 912.1) — approval/plan review requirements for engineered designs (see AHJ for specific submittal requirements).
§ 903.1 and Table 701.2 — materials and standards for vent pipe and fittings (materials limitations and referenced standards).
§ 1005.1 — trap seal depth requirements (minimum 2 in., typical range 2–4 in.) — relevant when evaluating trap seal protection and primers.
§ 1007.1–1007.2 — trap-seal primer requirements and acceptable devices (useful mitigation where traps are subject to evaporation or infrequent use).
§ 911.3 — relief vent sizing requirement for certain circuit-vented branches (useful if engineered system is providing relief venting for many fixtures).

(If you need the full text or the exact administrative submission checklist in § 301.5 or the full procedural language for permit review, request those sections and I will extract and cite them directly — the 912 language refers to § 301.5 but does not restate the permit items.)

Code references

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

CPC § 911.3 High relevance — show source text
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

Table 1002.2 Horizontal Lengths of Trap Arms . . . . . . . . . . . . . . . . . . . . . . .195

1003.2 Slip Joint Fittings . . . . . . . . . . . . .195

1003.3 Size . . . . . . . . . . . . . . . . . . . . . . . .195

1004.0 Traps . . . . . . . . . . . . . . . . . . . . . .196

1004.1 Prohibited . . . . . . . . . . . . . . . . . . .196

1004.2 Movable Parts . . . . . . . . . . . . . . . .196

1005.0 Trap Seals . . . . . . . . . . . . . . . . . .196

1005.1 General . . . . . . . . . . . . . . . . . . . . .196

1006.0 Floor Drain Traps . . . . . . . . . . . . .196

1006.1 General . . . . . . . . . . . . . . . . . . . . .196

1007.0 Trap Seal Protection . . . . . . . . . . .196

1007.1 General . . . . . . . . . . . . . . . . . . . . .196

1007.2 Trap Seal Primers . . . . . . . . . . . .196

1008.0 Building Traps . . . . . . . . . . . . . . . .196

1008.1 General . . . . . . . . . . . . . . . . . . . . .196
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 § 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 § 911.4.1.1 High relevance — show source text

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.)

Adopting Agency	BSC	BSC- CG	SFM	HCD	Col6	Col7	DSA	Col9	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	Col17	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting Agency	BSC	BSC- CG	SFM	1	2	1-AC	AC	SS	SS/CC	1	1R	2	3	4	5	6	6	6	6	6	6	6	6	6
Adopt Entire Chapter	X							X								X
Adopt Entire Chapter as amended (amended sections listed below)				X	X					X	X	X	X	X	X				X
Adopt only those sections that are listed below
Chapter/Section
1003.1 Exception 2				X	X
1010.2																			X
1010.3																			X
_1010.

CPC § 2404.11 High relevance — show source text
Exception: Where the type of fire-extinguishing system used requires such ventilation to be discontinued, air makeup and exhaust systems shall shut down and dampers shall close.

2404.11 Limited spraying spaces. Limited spraying spaces shall comply with Sections 2404.11.1 through 2404.11.4. 2404.11.1 Job size. The aggregate surface area to be sprayed shall not exceed 9 square feet (0.84 m [2] ).

2404.11.2 Frequency. Spraying operations shall not be of a continuous nature.

2404.11.3 Ventilation. Positive mechanical ventilation providing not fewer than six complete air changes per hour shall be installed. Such system shall meet the requirements of this code for handling flammable vapor areas. Explosion venting is not required.

2404.11.4 Electrical wiring. Electrical wiring within 10 feet (3048 mm) of the floor and 20 feet (6096 mm) horizontally of the limited spraying space shall be designed for Class I, Division 2 locations in accordance with the California Electrical Code .

SECTION 2405—DIPPING OPERATIONS

2405.1 General. Dip-tank operations shall comply with the requirements of Section 2403 and Sections 2405.2 through 2405.11.

2405.2 Location of dip-tank operations. Dip-tank operations conducted in buildings used for Group A, I or R occupancies shall be located in a room designed for that purpose, equipped with an approved automatic sprinkler system and separated vertically and horizontally from other areas in accordance with the California Building Code .

2405.3 Construction of dip tanks. Dip tanks shall be constructed in accordance with Sections 2405.3.1 through 2405.3.4.3 and NFPA 34. Dip tanks, including drain boards, shall be constructed of noncombustible material and their supports shall be of heavy metal, reinforced concrete or masonry. 2405.3.1 Overflow. Dip tanks greater than 150 gallons (568 L) in capacity or 10 square feet (0.93 m [2] ) in liquid surface area shall be equipped with a trapped overflow pipe leading to an approved location outside the building. The bottom of the overflow connection shall be not less than 6 inches (152 mm) below the top of the tank.

2405.3.2 Bottom drains. Dip tanks greater than 500 gallons (1893 L) in liquid capacity shall be equipped with bottom drains that are arranged to automatically and manually drain the tank quickly in the event of a fire unless the viscosity of the liquid at normal atmospheric temperature makes this impractical. Access to the manual operation shall be from a safe location. Where gravity flow is not practicable, automatic pumps shall be provided. Such drains shall be trapped and discharged to a closed, vented salvage tank or to an approved outside location.

Exception: Dip tanks containing Class IIIB combustible liquids where the liquids are not heated above room temperature and the process area is protected by automatic sprinklers.

2405.3.3 Dipping liquid temperature control. Protection against the accumulation of vapors, self-ignition and excessively high temperatures shall be provided for dipping liquids that are heated directly or heated by the surfaces of the object being dipped.

2405.3.4 Dip-tank covers. Dip-tank covers allowed by Section 2405.4.1 shall be capable of manual operation and shall be automatic closing by approved automatic-closing devices designed to operate in the event of a fire.
California Plumbing Code High relevance — show source text
PG&E’s preferred PS arrangements are either: a) when the PS customer’s primary distribution line is underground (UG) and the POS is less than 500 feet from the property line, or b) when the PS customer’s primary distribution line is overhead (OH) and the protective device pole (if separate from the POS pole) is less than 50 feet from the property line.
1. UG Conductor and POS < 500 Feet
If the PS customer’s primary line is underground and the POS is 500 feet or less from the property line, refer to Figure 1 on Page 12 and Figure 2 on Page 13. The following requirements apply:

A. The PS customer must provide a PG&E approved pad−mounted switchgear enclosure for PG&E’s revenue−metering equipment. See Section 12 on Page 13 for detailed revenue− metering requirements.

B. The PS customer must install primary protection at the POS. This protection may consist of a circuit breaker with phase and ground relays or, depending on the customer’s load, fuses may suffice. If PG&E determines that fuses will not coordinate with PG&E’s source−side protection, then the customer must use a circuit breaker. See Section 8A on Page 6 and Section 8C on Page 7 for circuit breaker and fuse requirements.

C. The PS customer must install conduit from the POS to PG&E’s primary distribution equipment location.

D. PG&E will pull one continuous run of cable and connect to the customer’s POS termination facility, not to exceed 500 feet (subject to an acceptable number of bends in the conduit).
1. OH Conductor
If the PS customer’s primary line is overhead, then the first pole at the customer’s property line is the POS. Refer to Figure 3. The following requirements apply:

A. PG&E will install pole−top revenue−metering on the first pole on the PS customer’s property. See Engineering Standard 058779 Pole−Top Primary Metering Installation, (12 or 21 kV Line) for pole−top revenue− metering requirements.

B. The PS customer must install primary protection on the second pole on their property, not to exceed 50 feet from the revenue metering pole. This protection may consist of a recloser or, depending on the customer’s load, fuses may suffice. If PG&E determines that fuses will not coordinate with PG&E’s source−side protection, then the customer must use a recloser. See Section 8C on Page 7 for recloser requirements.

C. The PS customer second pole and the equipment installed on it, must maintain a minimum clearance of 10 feet from the PG&E revenue metering pole and any equipment, crossarms, and wires installed on it.

D. PG&E will interconnect its system with the customer’s system at the revenue−metering pole.

Section 4 Non−Preferred PS Arrangement Proposals

PS customers may propose a non−preferred PS arrangement. This typically occurs when the PS customer’s primary distribution line is UG and the proposed location for the primary switchgear is greater than 500 feet from the property line. PG&E will consider such proposals; however, non−preferred service arrangement proposals may take longer to

094676 Page 2 of 16 Rev. #00: 3/25/2022
CPC § 11.5 High relevance — show source text
5-foot
level of storage
3.
Locate in
longitudinal flue
space,
staggered
vertical
4.
Shields required
where multiple-
level|1.
Ordinary
temperature,
quick-response
sprinklers,
maximum 8 feet
3 inches
horizontal
spacing
2.
One line of
sprinklers at the
6-foot level and
the 11.5-foot
level of storage
3.
Locate in
longitudinal flue
space,
staggered
vertical
4.
Shields required
where multiple-
level| |TABLE 5704.3.6.3(8)—AUTOMATIC SPRINKLER PROTECTION REQUIREMENTS FOR
CLASS I LIQUID STORAGE IN METAL CONTAINERS OF 1-GALLON CAPACITY OR LESS WITH UNCARTONED
OR CASE-CUT SHELF DISPLAY UP TO 6.5 FEET, AND PALLETIZED STORAGE ABOVE IN A DOUBLE-ROW RACK ARRAYa|CEILING SPRINKLER DESIGN AND DEMAND|Maximum
spacing|Maximum
spacing|100 ft2/head|100 ft2/head| |TABLE 5704.3.6.3(8)—AUTOMATIC SPRINKLER PROTECTION REQUIREMENTS FOR
CLASS I LIQUID STORAGE IN METAL CONTAINERS OF 1-GALLON CAPACITY OR LESS WITH UNCARTONED
OR CASE-CUT SHELF DISPLAY UP TO 6.5 FEET, AND PALLETIZED STORAGE ABOVE IN A DOUBLE-ROW RACK ARRAYa|CEILING SPRINKLER DESIGN AND DEMAND|Area
(square feet)|Ordinary
temperature|Not
Applicable|Not
Applicable| |TABLE 5704.3.6.3(8)—AUTOMATIC SPRINKLER PROTECTION REQUIREMENTS FOR
CLASS I LIQUID STORAGE IN METAL CONTAINERS OF 1-GALLON CAPACITY OR LESS WITH UNCARTONED
OR CASE-CUT SHELF DISPLAY UP TO 6.5 FEET, AND PALLETIZED STORAGE ABOVE IN A DOUBLE-ROW RACK ARRAYa|CEILING SPRINKLER DESIGN AND DEMAND|Area
(square feet)|High
temperature|2,000b|2,000b| |TABLE 5704.3.6.3(8)—AUTOMATIC SPRINKLER PROTECTION REQUIREMENTS FOR
CLASS I LIQUID STORAGE IN METAL CONTAINERS OF 1-GALLON CAPACITY OR LESS WITH UNCARTONED
OR CASE-CUT SHELF DISPLAY UP TO 6.5 FEET, AND PALLETIZED STORAGE ABOVE IN A DOUBLE-ROW RACK ARRAYa|CEILING SPRINKLER DESIGN AND DEMAND|Density
(gpm/ft2)|Density
(gpm/ft2)|0.60|0.60| |**TABLE 5704.3.6.
CPC § 509.6.1 High relevance — show source text
A Type B vent or listed chimney lining system passing through an unused masonry chimney flue shall not be considered to be exposed to the outdoors. Where vents extend outdoors above the roof more than 5 feet (1524 mm) higher than required by Table 509.6.1, and where vents terminate in accordance with Section 509.6.1(1)(b), the outdoor portion of the vent shall be enclosed as required by this paragraph for vents not considered to be exposed to the outdoors, or such venting system shall be engineered. A Type B vent passing through an unventilated enclosure or chase insulated to a value of not less than R-8 shall not be considered to be exposed to the outdoors. Table 510.1.2(3) in combination with Table 510.1.2(6) shall be used for claytilelined exterior masonry chimneys, provided all of the following requirements are met:

(1) The vent connector is Type B double wall.

(2) The vent connector length is limited to 18 inches per inch (18 mm/mm) of vent connector diameter.

2025 CALIFORNIA PLUMBING CODE 105

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WATER HEATERS

(3) The appliance is draft hood equipped.

(4) The input rating is less than the maximum capacity given in Table 510.1.2(3).

(5) For a water heater, the outdoor design temperature shall not be less than 5°F (-15°C).

(6) For a space-heating appliance, the input rating is greater than the minimum capacity given by Table 510.1.2(6). [NFPA 54:13.1.11] 510.1.11 Corrugated Vent Connector Size. Corrugated vent connectors shall not be smaller than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. [NFPA 54:13.1.12]

510.1.12 Upsizing. Vent connectors shall not be upsized more than two sizes greater than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. [NFPA 54:13.1.13]

510.1.13 Multiple Vertical Vent Sizes. In a single run of vent or vent connector, more than one diameter and type shall be permitted to be used, provided that all the sizes and types are permitted by the tables. [NFPA 54:13.1.14]

510.1.14 Interpolation. Interpolation shall be permitted in calculating capacities for vent dimensions that fall between table entries. [NFPA 54:13.1.15]

510.1.15 Extrapolation. Extrapolation beyond the table entries shall not be permitted. [NFPA 54:13.1.16] 510.1.16 Sizing Vents Not Covered by Tables. Where a vent height is lower than 6 feet (1829 mm) or higher than shown in Table 510.1.2(1) through Table 510.2(9), an engineering method shall be used to calculate the vent capacity. [NFPA 54:13.1.17]
CPC § 2025 High relevance — show source text
Appendix A Recommended Rules for Sizing the Water Supply System.

Appendix A provides a method of sizing the water supply and distribution system that provides precise calculations to establish the proper pressures and flow to the system’s fixtures. The goal of sizing the system is to deliver an acceptable volume of water to the most hydraulically remote fixture during minimum pressure and maximum flow conditions; provide satisfactory water pressure to the most hydraulically remote fixture during minimum pressure and maximum flow conditions; and to prevent excessive water velocity during maximum flow conditions.

Appendix B Explanatory Notes on Combination Waste and Vent Systems.

Appendix B contains general guidelines for the design and installation of combination waste and vent systems. These systems are designed for waste piping and are purposely oversized to serve as both a waste and vent pipe to avoid excessive pneumatic effects at fixture drains.

Appendix C Alternate Plumbing Systems.

The intent of this appendix is to provide clarification of procedures for the design and approval of engineered plumbing systems, alternate materials, and equipment that are not specifically covered in other parts of the code. Alternative methods are allowed to be used where approved by the authority having jurisdiction. Approval of alternatives is based on a demonstration showing that the method or material used is at least equivalent in strength, deflection, and capacity to that provided by the prescriptive methods and materials.

Appendix D Sizing Storm Water Drainage Systems.

Appendix D provides general guidelines for the sizing of stormwater drainage systems. There are two pieces of information that must always be a given. They are the roof size and the rate of rainfall for the area.

2025 CALIFORNIA PLUMBING CODE xvii

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FORMAT OF THE UNIFORM PLUMBING CODE

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

The provisions of this appendix apply to the plumbing and drainage systems of mobile home and recreational vehicle parks. These provisions also apply to the use, maintenance, and installation for supplying fuel gas, water, electricity, and disposal of sewage from accessory buildings or structures, and building components.

Appendix F Firefighter Breathing Air Replenishment Systems.

Appendix F provides guidance on installing firefighter breathing air replenishment systems. System components include outside fire department connection panel, interior air fill panel or station, interconnected piping distribution system and pressure monitoring switch. Fire departments access the system through an outside connection panel and are able to pump air into the system. The firefighters inside the structure access the system at fill stations that are found throughout the building. The piping distribution system is made from stainless tubing or other approved materials. It delivers compressed air to the building’s interior air-fill stations and interior air-fill panels. The tubing also acts as a conduit in the interior of the building between the outside connection panel and the air storage system. If the system becomes over-pressurized, the air monitoring system also acts as a pressure relief. A system isolation valve is placed alongside each interior air fill station and interior air fill panel to isolate the system.

Appendix G Sizing of Venting Systems.

Appendix G provides added information on the sizing of gas vents. This appendix is useful to the end user for the proper sizing of venting systems. A series of examples are given that show how to use the tables and other requirements of Chapter 5.

Appendix H Private Sewage Disposal Systems.
CPC § 2.25 High relevance — show source text
00|2.25|0.70|DR|3.70|1.05|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|33 mil cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|16|3.85|1.45|DR|DR|3.40|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|33 mil cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|24|3.40|DR|DR|DR|2.70|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|12|3.00|1.80|DR|DR|3.00|0.65|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|16|3.00|1.00|DR|DR|2.85|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|24|2.85|DR|DR|DR|2.20|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|12|4.00|3.85|2.80|1.80|4.00|3.05|1.50|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|16|4.00|3.30|1.95|0.60|4.00|2.25|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|24|4.00|2.25|DR|DR|4.00|0.65|DR|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = Design Required, o.c. = on center.
a. Wood furring shall be spruce-pine-fir or any softwood species with a specific gravity of 0.42 or greater.
CPC § 701.4 High relevance — show source text
701.4 Indoor Combustion Air . . . . . . . . . 147

701.5 Indoor Opening Size and Location . . . . . . . . . . . . . . . . . . . . 147

701.6 Outdoor Combustion Air . . . . . . . . 147

701.7 Combination Indoor and Outdoor

Combustion Air . . . . . . . . . . . . . . . 148

701.8 Engineered Installations . . . . . . . . 149

701.9 Mechanical Combustion Air

Supply. . . . . . . . . . . . . . . . . . . . . . 149

701.10 Louvers, Grilles, and Screens . . . 149

701.11 Combustion Air Ducts. . . . . . . . . . 150

701.12 Dampers Prohibited . . . . . . . . . . . 150

702.0 Extra Device or Attachment . . . . . 150

702.1 General. . . . . . . . . . . . . . . . . . . . . 150

CHAPTER 8 CHIMNEYS AND VENTS. . . . . . . 151

801.0 General. . . . . . . . . . . . . . . . . . . . . 153

801.1 Applicability. . . . . . . . . . . . . . . . . . 153

801.2 Venting of Gas Appliances . . . . . . 153

801.3 Appliances Fueled by Other Fuels. 153

802.0 Venting of Appliances. . . . . . . . . . 153

xxxiv

802.1 Listing . . . . . . . . . . . . . . . . . . . . . . 153

802.2 Connection to Venting Systems . . 153

802.3 Minimum Safe Performance . . . . . 153

802.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . . . . 154

802.5 Masonry, Metal, and Factory-Built Chimneys . . . . . . . . . . . . . . . . . . . 154

Table 802.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . . . . 155

802.6 Gas Vents. . . . . . . . . . . . . . . . . . . 157

Table 802.6.1 Roof Slope Heights. . . . . . . . . . . . 158

802.7 Single-Wall Metal Pipe . . . . . . . . . 159

Table 802.7.3.3 Clearance for Connectors. . . . . . . 160

802.8 Through-the-Wall Vent Termination . . . . . . . . . . . . . . . . . . 160

802.9 Condensation Drain . . . . . . . . . . . 160

802.10 Vent Connectors for Category I Appliances . . . . . . . . . . . . . . . . . . 160

Table 802.10.1.3 Minimum Thickness for Galvanized

Steel Vent Connectors for Low Heat Appliances . . . . . . . . . . . . . . 161
CPC § 5004.7.2 Medium relevance — show source text
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.

50-24 2025 CALIFORNIA FIRE CODE

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

HAZARDOUS MATERIALS—GENERAL PROVISIONS

5004.9 Emergency alarm. An approved manual emergency alarm system shall be provided in buildings, rooms or areas used for storage of hazardous materials. Emergency alarm-initiating devices shall be installed outside of each interior exit or exit access door of storage buildings, rooms or areas. Activation of an emergency alarm-initiating device shall sound a local alarm to alert occupants of an emergency situation involving hazardous materials.

5004.10 Supervision and monitoring. Emergency alarm, detection and automatic fire-extinguishing systems required by Section 5004 shall be electrically supervised and monitored by an approved supervising station or, where approved, shall initiate an audible and visual signal at a constantly attended on-site location.

5004.11 Clearance from combustibles. The area surrounding an outdoor storage area or tank shall be kept clear of combustible materials and vegetation for a minimum distance of 25 feet (7620 mm).

5004.12 Noncombustible floor. Except for surfacing, floors of storage areas shall be of noncombustible construction.

5004.13 Weather protection. Where overhead noncombustible construction is provided for sheltering outdoor hazardous material storage areas, such storage shall not be considered indoor storage where the area is constructed in accordance with the requirements for weather protection as required by the California Building Code .

Exception: Storage of explosive materials shall be considered as indoor storage.

5004.14 Outdoor storage location. Outdoor storage areas for hazardous materials shall be located as required by Section 5003.12 except where material-specific requirements, including requirements in referenced standards, are provided in other chapters of this code.

SECTION 5005—USE, DISPENSING AND HANDLING

5005.1 General. Use, dispensing and handling of hazardous materials in amounts exceeding the maximum allowable quantity per control area set forth in Section 5003.1 shall be in accordance with Sections 5001, 5003 and 5005. Use, dispensing and handling of hazardous materials in amounts not exceeding the maximum allowable quantity per control area set forth in Section 5003.1 shall be in accordance with Sections 5001 and 5003.

5005.1.1 Separation of incompatible materials. Separation of incompatible materials shall be in accordance with Section 5003.9.8.
CPC § 901.1 Medium relevance — show source text
901.1 Applicability. This chapter shall govern the materials, design, and installation of plumbing vent systems. 901.2 Vents Required. Each plumbing fixture trap, except as otherwise provided in this code, shall be protected against siphonage and backpressure, and air circulation shall be ensured throughout all parts of the drainage system by means of vent pipes installed in accordance with the requirements of this chapter and as otherwise required by this code. 901.3 Trap Seal Protection. The vent system shall be designed to prevent a trap seal from being exposed to a pressure differential that exceeds 1 inch water column (0.24 kPa) on the outlet side of the trap.

902.0 Vents Not Required.

902.1 Interceptor. Vent piping shall be permitted to be omitted on an interceptor where such interceptor acts as a primary settling tank and discharges through a horizontal indirect waste pipe into a secondary interceptor. The second interceptor shall be properly trapped and vented. 902.2 Bars, Soda Fountains, and Counter. Traps serving sinks that are part of the equipment of bars, soda fountains, and counters need not be vented where the location and construction of such bars, soda fountains, and counters are such as to make it impossible to do so. Where such conditions exist, said sinks shall discharge using approved indirect waste pipes into a floor sink or other approved type of recep tor.

903.0 Materials.

903.1 Applicable Standards. Vent pipe and fittings shall comply with the applicable standards referenced in Table 701.2, except that:

(1) No galvanized steel or 304 stainless steel pipe shall be installed underground and shall be not less than 6 inches (152 mm) aboveground.

(2) ABS and PVC DWV piping installations shall be in accordance with the firestop protection requirements in the California Building Code . Except for individual single-family dwelling units, materials exposed within ducts or plenums shall have a flame-spread index of not more than 25 and a smoke-developed index of not more than 50 where tested in accordance with ASTM E84 or UL 723. Plastic piping installed in plenums shall be tested in accordance with all requirements of ASTM E84 or UL 723. Mounting methods, supports and sample sizes of materials for testing that are not specified in ASTM E84 or UL 723 shall be prohibited.

903.1.1 [HCD 1 & HCD 2] ABS or PVC installations are limited to not more than two stories of areas of resi- dential accommodation.

903.1.2 [HCD 1] All malleable iron vents shall be gal- vanized.

903.1.3 [OSHPD 1, 2, 3, 4 & 5] ABS and PVC instal- lations are not allowed.

903.2 Use of Copper or Copper Alloy Tubing. Copper or copper alloy tube for underground drainage and vent piping shall have a weight of not less than that of copper or copper alloy drainage tube type DWV. 903.2.1 Aboveground. Copper or copper alloy tube for aboveground drainage and vent piping shall have a weight of not less than that of copper or copper alloy drainage tube type DWV. 903.2.2 Prohibited Use. Copper or copper alloy tube shall not be used for chemical or industrial wastes as

defined in Section 811.0.

Frequently asked questions

Who can prepare an engineered vent design?

A registered design professional must prepare the engineered vent system (signed and sealed), as required by § 912.1.

What is the single quantitative performance requirement I must meet?

Prevent trap outlet-side pressure differential from exceeding 1 inch water column (0.24 kPa) per § 901.3; § 912.2 explicitly requires compliance with § 901.3.

Do engineered vent systems bypass plan review?

No — engineered systems must be approved in accordance with the administrative approval process referenced in § 912.1 (see § 301.5).

Can I use nonstandard materials in an engineered vent system?

Materials still must meet the CPC referenced standards and material rules (see § 903.1 and Table 701.2); engineered design does not waive material requirements.

If my analysis shows 1.1 in. WC at a trap, is that acceptable?

No — § 901.3 sets 1.0 in. WC as the maximum. If analysis predicts 1.1 in. WC, revise the design (vent capacity, relief vent, trap primer, etc.) so predicted transient pressures are ≤ 1.0 in. WC.

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