Appendix C — ALTERNATE PLUMBING SYSTEMS — 2025 California Plumbing Code (Title 24, Part 5)

(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			DSA			OSHPD							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
Adopt Entire Chapter as amended (amended sections listed below)
Adopt only those sections that are listed below
Chapter/Section

This state agency does not adopt sections identified with 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 1.11.0.

386 2025 CALIFORNIA PLUMBING CODE

APPENDIX C

ALTERNATE PLUMBING SYSTEMS

The provisions contained in this appendix are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance.

C 101.0 General.

C 101.1 Applicability. The intent of this appendix is to provide clarification of procedures for the design and approval of engineered plumbing systems, alternate materials, and equipment not specifically covered in other parts of the code. C 101.2 Provisions. The provisions of this appendix apply to the design, installation, and inspection of an engineered plumbing system, alternate material, and equipment. C 101.3 Authority Having Jurisdiction. The Authority Having Jurisdiction has the right to require descriptive details of an engineered plumbing system, alternate material, or equipment including pertinent technical data to be filed. C 101.4 Standards and Specifications. Components, materials, and equipment shall comply with standards and specifications listed in Chapter 17 of this code and other national consensus standards applicable to plumbing systems and materials.

C 101.5 Alternate Materials and Equipment. Where such standards and specifications are not available, alternate materials and equipment shall be approved in accordance with the provisions of Section 301.3 of this code.

C 201.0 Definitions.

C 201.1 General. For the purpose of this appendix, the following definitions shall apply: Branch Interval. A length of soil or waste stack corresponding in general to a story height, but in no case less than 8 feet (2438 mm), within which the horizontal branches from one floor or story of the building are connected to the stack. Engineered Plumbing System. A system designed for a specific building project with drawings and specifications indicating plumbing materials to be installed, all as prepared by a registered design professional.

C 301.0 Engineered Plumbing Systems. C 301.1 Inspection and Installation. In other than oneand two-family dwellings, the designer of the system is to provide periodic inspection of the installation on a schedule approved by the Authority Having Jurisdiction. Prior to the final approval, the designer shall verify to the Authority Having Jurisdiction that the installation is in accordance with the approved plans, specifications, and data and such amendments to it. The designer shall certify to the Authority Having Jurisdiction that the installation is in accordance with the applicable engineered design criteria. C 301.2 Owner Information. The designer of the system shall provide the building owner with information concerning the system, considerations applicable for subsequent modifications to the system, and maintenance requirements as applicable.

C 302.0 Water Heat Exchangers. C 302.1 Protection from Contamination. Heat exchangers used for heat transfer, heat recovery, or solar heating shall protect the potable water system from being contaminated by the heat-transfer medium.

C 302.2 Single-Wall Heat Exchangers. Single-wall heat exchangers shall comply with the following requirements:

(1) The heat-transfer medium is either potable water or contains essentially nontoxic transfer fluids having a toxicity rating or class of 1 (see Section 207.0).

(2) The pressure of the heat-transfer medium is maintained at less than the normal minimum operating pressure of the potable water system.

Exception: Steam in accordance with Section C 302.2(1) above.

(3) The equipment is permanently labeled to indicate that only additives recognized as safe by the FDA shall be used in the heat-transfer medium.

C 302.3 Alternate Designs. Other heat exchanger designs shall be permitted where approved by the Authority Having Jurisdiction.

C 303.0 Fixture Unit Values for Private or Private Use Bathroom Groups.

C 303.1 Fixtures. Table C 303.2 and Table C 303.3 reflect the fixture unit loads for the fixtures in bathrooms as groups, rather than as individual fixtures. Such fixtures include water closets, lavatories, and bathtubs or showers. The tables reflect diversity in the use of fixtures within a bathroom and between multiple bathrooms. C 303.2 Water Supply Fixture Unit Values. The listed water supply fixture unit values in Table C 303.2 reflect the load of entire bathroom groups on the cold water building supply. Individual hot and cold water branch piping to the fixtures shall be permitted to be sized in accordance with Chapter 6 and Appendix A. C 303.3 Drainage Fixture Unit Values. The listed drainage fixture unit values in Table C 303.3 reflect a load of entire bathroom groups on the sanitary drainage system. Where fixtures within bathrooms connect to different branches of the drainage system, the fixture unit values for the individual fixtures shall be used, as listed in Table 702.1 of this code.

C 304.0 Drainage System Sizing.

C 304.1 Drainage Fixture Units. Drainage fixture unit values shall be sized in accordance with Section 702.0 and

Table 702.1.

APPENDIX C

TABLE C 303.2 WATER SUPPLY FIXTURE UNITS (WSFU) FOR BATHROOM GROUPS [1, 2]

	PRIVATE USE BATHROOM GROUP		SERVING 3 OR MORE PRIVATE USE BATHROOM GROUPS
	COLD	HOT3	COLD	HOT
Bathroom Groups Having up to 1.6 GPF Gravity-Tank and Pressure Tank Water Closets
Half-Bath or Powder Room	3.5	0.8	2.5	0.5
1 Bathroom Group	5.0	2.5	3.5	1.8
11⁄2 Bathrooms	6.0	2.5	3.0	3.0
2 Bathrooms	7.0	3.5	3.4	3.4
21⁄2 Bathrooms	8.0	3.6	3.8	3.8
3 Bathrooms	9.0	4.5	4.1	4.1
Each Additional1⁄2 Bath	0.5	0.1	0.4	0.4
Each Additional Bathroom Group	1.0	0.5	0.8	0.8
Other Groups of Fixtures	Other Groups of Fixtures	Other Groups of Fixtures	Other Groups of Fixtures	Other Groups of Fixtures
Bathroom Group (1.6 GPF Flushometer Value)	6.0	2.5	4.0	1.7
Kitchen Group (Sink and Dishwasher)	2.0	2.0	1.5	1.5
Laundry Group (Sink and Clothes Washer)	5.0	5.0	3.0	3.0

Notes: 1 A bathroom group, for this table, consists of one water closet, up to two lavatories, and either one bathtub or one shower. 2 A half-bath or powder room, for this table, consists of one water closet and one lavatory. 3 Multi-unit dwellings with individual water heaters use the same WSFU as for individual dwellings.

C 304.2 Size of Building Drain and Building Sewer. The maximum number of drainage fixture units allowed on the building drain or building sewer of a given size shall be in accordance with Table C 304.2. The size of a building drain or building sewer serving a water closet shall be not less than 3 inches (80 mm).

C 304.3 Size of Horizontal Branch or Vertical Stack. The maximum number of drainage fixture units allowed on a horizontal branch or vertical soil or waste stack of a given size shall be in accordance with Table C 304.3. Stacks shall

be sized based on the total accumulated connected load at each story or branch interval.

C 304.3.1 Horizontal Stack Offsets. Horizontal

stack offsets shall be sized in accordance with Table C 304.2 as required for building drains.

C 304.3.2 Vertical Stack Offsets. Vertical stack off sets shall be sized in accordance with Table C 304.3 as required for stacks.

C 304.4 Horizontal Stack Offset and Horizontal Branch

Connections. Horizontal branch connections shall not connect to a horizontal stack offset or within 2 feet (610 mm) above or below the offset where such horizontal offset is located more than four branch intervals below the top of the stack.

C 401.0 Vent System Sizing. C 401.1 Size of Vents. The size of vent piping shall be determined from the developed length and the total number of drainage fixture units connected in accordance with Table C 401.1. Vents shall be not less than one-half the required size of the drainage pipe size served as determined by Table C 304.3 for horizontal fixture branches and stacks nor less than 1 [1] ⁄ 4 inches

(32 mm) in diameter. The drainage system shall be vented by not less than one vent pipe which shall be not less than one-half the size of the required building drain and which shall extend from the building drain or extension of building drain to the outdoors. Vents shall be installed in accordance with Chapter 9. C 401.2 Vent Stack. A vent stack shall be required for a drainage stack that extends five or more branch intervals above the building drain or horizontal branch. The developed length of the vent stack shall be measured from the lowest connection of a branch vent to the termination outdoors.

C 401.3 Branch Vents. Where branch vents exceed 40 feet (12 192 mm) in developed length, such vent shall be increased by one pipe size for the entire developed length of the vent pipe. C 401.4 Venting Horizontal Offsets. Drainage stacks with horizontal offsets shall be vented where five or more branch intervals are located above the offset. The upper and lower section of the horizontal offset shall be vented in accordance

with Section C 401.4.1 and Section C 401.4.2.

C 401.4.1 Venting Upper Section. The vent for the upper section of the stack shall be vented as a separate stack with a vent stack connection installed at the base of the drainage stack. Such vent stack shall connect below the lowest horizontal branch or building drain. Where vent stack connects to the building drain, the connection shall be located downstream of the drainage stack and within a distance of 10 times the diameter of the drainage stack. C 401.4.2 Venting Lower Section. The vent for the lower section of the stack shall be vented by a yoke vent connecting between the offset and the next lower horizontal branch using a wye-branch fitting. The size of the yoke vent and connection shall be not less in diameter

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APPENDIX C

TABLE C 303.3 DRAINAGE FIXTURE UNIT VALUES (DFU) FOR BATHROOM GROUPS [1, 2]

	PRIVATE USE BATHROOM GROUP	SERVING 3 OR MORE PRIVATE USE BATHROOM GROUP
Bathroom Groups having 1.6 GPF Gravity-Tank Water Closets
Half-Bath or Powder Room	3.0	2.0
1 Bathroom Group	5.0	3.0
11⁄2 Bathrooms	6.0	3.5
2 Bathrooms	7.0	4.5
21⁄2 Bathrooms	8.0	5.0
3 Bathrooms	9.0	5.5
Each Additional1⁄2 Bath	0.5	0.5
Each Additional Bathroom Group	1.0	1.0
Bathroom Groups having 1.6 GPF Pressure-Tank Water Closets
Half-Bath or Powder Room	3.5	2.5
1 Bathroom Group	5.5	3.5
11⁄2 Bathrooms	6.5	4.0
2 Bathrooms	7.5	5.0
21⁄2 Bathrooms	8.5	5.5
3 Bathrooms	9.5	6.0
Each Additional1⁄2 Bath	0.5	0.5
Each Additional Bathroom Group	1.0	1.0
Bathroom Groups having 3.5 GPF Gravity-Tank Water Closets
Half-Bath or Powder Room	3.0	2.0
1 Bathroom Group	6.0	4.0
11⁄2 Bathrooms	8.0	5.5
2 Bathrooms	10.0	6.5
21⁄2 Bathrooms	11.0	7.5
3 Bathrooms	12.0	8.0
Each Additional1⁄2 Bath	0.5	0.5
Each Additional Bathroom	1.0	1.0
Bathroom Group (1.6 GPF Flushometer Valve)	3.0	3.0
Bathroom Group (3.5 GPF Flushometer Valve)	4.0	4.0

Notes:

1 A bathroom group, for this table, consists of not more than one water closet, up to two lavatories, and either one bathtub or one shower.

2 A half-bath or powder room, for this table, consists of one water closet and one lavatory.

APPENDIX C

	TABLE C 304.2 BUILDING DRAINS AND BUILDING SEWERS1
DIAMETER OF PIPE (inches)	MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS FOR SANITARY BUILDING DRAINS AND RUNOUTS FROM STACKS	MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS FOR SANITARY BUILDING DRAINS AND RUNOUTS FROM STACKS	MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS FOR SANITARY BUILDING DRAINS AND RUNOUTS FROM STACKS	MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS FOR SANITARY BUILDING DRAINS AND RUNOUTS FROM STACKS
DIAMETER OF PIPE (inches)	SLOPE (inches per foot)	SLOPE (inches per foot)	SLOPE (inches per foot)	SLOPE (inches per foot)
DIAMETER OF PIPE (inches)	1⁄16	1⁄8	1⁄4	1⁄2
2	–	–	21	26
21⁄2	–	–	24	31
3	–	20	422	502
4	–	180	216	250
5	–	390	480	575
6	–	700	840	1000
8	1400	1600	1920	2300
10	2500	2900	3500	4200
12	3900	4600	5600	6700
15	7000	8300	10 000	12 000

For SI units: 1 inch = 25 mm, 1 inch per foot = 83.3 mm/m

Notes:

1 On-site sewers that serve more than one building shall be permitted to be sized according to the current standards and specifications of the administrative authority for public sewers.

2 A maximum of two water closets or two bathroom groups, except in single-family dwellings, where a maximum of three water closets or three bathroom groups shall be permitted to be installed.

	TABLE C 304.3 HORIZONTAL FIXTURE BRANCHES AND STACKS
DIAMETER OF PIPE (inches)	MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS	MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS	MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS	MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS
DIAMETER OF PIPE (inches)	HORIZONTAL FIXTURE BRANCH1	ONE STACK OF THREE OR FEWER BRANCH INTERVALS	STACKS WITH MORE THAN THREE BRANCH INTERVALS	STACKS WITH MORE THAN THREE BRANCH INTERVALS
DIAMETER OF PIPE (inches)	HORIZONTAL FIXTURE BRANCH1	ONE STACK OF THREE OR FEWER BRANCH INTERVALS	TOTAL FOR STACK	TOTAL AT ONE BRANCH INTERVAL
11⁄2	3	4	8	2
2	6	10	24	6
21⁄2	12	20	42	9
3	202	482	722	202
4	160	240	500	90
5	360	540	1100	200
6	620	960	1900	350
8	1400	2200	3600	600
10	2500	3800	5600	1000
12	3900	6000	8400	1500
15	7000	6000	8400	1500

For SI units: 1 inch = 25 mm

Notes:

1 Does not include branches of the building drain.

2 A maximum of two water closets or bathroom groups within each branch interval or more than six water closets or bathroom groups on the stack.

than the required size for the vent serving the drainage stack. The yoke vent connection shall be permitted to be a vertical extension of the drainage stack.

C 501.0 Vacuum Drainage Systems. C 501.1 General. This section regulates the design and installation provisions for vacuum waste drainage systems. Plans for vacuum waste drainage systems shall be submitted to the Authority Having Jurisdiction for approval and shall be considered an engineered designed system. Such plans shall be prepared by a registered design professional to per

form plumbing design work. Details are necessary to ensure compliance with the requirements of this section, together with a full description of the complete installation including quality, grade of materials, equipment, construction, and methods of assembly and installation. Components, materials, and equipment shall comply with standards and specifications listed in Chapter 17 of this code or approved by the Authority Having Jurisdiction and other national consensus standards applicable to plumbing systems and materials. Where such standards and specifications are not available, alternate materials and equipment shall be approved in accordance with Section 301.3.

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APPENDIX C

		TABLE C 401.1 SIZE AND LENGTH OF VENTS
SIZE OF SOIL OR WASTE STACK (inches)	FIXTURE UNITS CONNECTED	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)
SIZE OF SOIL OR WASTE STACK (inches)	FIXTURE UNITS CONNECTED	11⁄4	11⁄2	2	21⁄2	3	4	5	6	8
SIZE OF SOIL OR WASTE STACK (inches)	FIXTURE UNITS CONNECTED	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)
11⁄2	8	50	150	––	––	––	––	––	––	––
2	12	30	75	200	––	––	––	––	––	––
2	20	26	50	150	––	––	––	––	––	––
21⁄2	42	––	30	100	300	––	––	––	––	––
3	10	––	30	100	100	600	––	––	––	––
3	30	––	––	60	200	500	––	––	––	––
3	60	––	––	50	80	400	––	––	––	––
4	100	––	––	35	100	260	1000	––	––	––
4	200	––	––	30	90	250	900	––	––	––
4	500	––	––	20	70	180	700	––	––	––
5	200	––	––	––	35	80	350	1000	––	––
5	500	––	––	––	30	70	300	900	––	––
5	1100	––	––	––	20	50	200	700	––	––
6	350	––	––	––	25	50	200	400	1300	––
6	620	––	––	––	15	30	125	300	1100	––
6	960	––	––	––	––	24	100	250	1000	––
6	1900	––	––	––	––	20	70	200	700	––
8	600	––	––	––	––	––	50	150	500	1300
8	1400	––	––	––	––	––	40	100	400	1200
8	2200	––	––	––	––	––	30	80	350	1100
8	3600	––	––	––	––	––	25	60	250	800
10	1000	––	––	––	––	––	––	75	125	1000
10	2500	––	––	––	––	––	––	50	100	500
10	3800	––	––	––	––	––	––	30	80	350
10	5600	––	––	––	––	––	––	25	60	250

For SI units: 1 inch = 25 mm, 1 foot = 304.8 mm

C 501.2 System Design. Vacuum waste drainage systems shall be designed and installed in accordance with the manufacturer’s installation instructions. A vacuum waste drainage system shall include a vacuum generating system, waste collection center, piping network, vacuum valve, and control components used to isolate the vacuum piping network from atmospheric pressure and to collect waste at its point of origin. Where a vacuum system provides the only means of sanitation, the duplicate vacuum generating equipment set to operate automatically shall be installed to allow the system to continue in operation during periods of maintenance. C 501.2.1 Vacuum Generating System. The vacuum generating station shall include vacuum pumps to create a constant vacuum pressure within the piping network and storage tanks. The operation of pumps, collection tanks, and alarms shall be automated by controls. The vacuum pumps shall be activated on demand and accessible for repair or replacement. The vent from the vacuum pump shall be provided for vacuum pump air exhaust and shall be of a size capable of handling the total air volume of the vacuum pump.

C 501.2.2 Waste Collection Center or Storage Tanks. Vacuum collection center or storage tanks shall

be of such capacity as to provide storage of waste to prevent fouling of the system. Such collection or storage tank shall be capable of withstanding 150 percent of the rated vacuum (negative pressure) created by the vacuum source without leakage or collapse. Waste collection center or storage tanks shall be accessible for adjustment, repair, or replacement.

C 501.2.3 Piping Network. The piping network shall be under a continuous vacuum and shall be designed to withstand 150 percent of the vacuum (negative pressure) created by the vacuum source within the system without leakage or collapse. Sizing the piping network shall be in accordance with the manufacturer’s instructions. The water closet outlet fitting shall connect with a piping network having not less than an 1 [1] ⁄ 2 inch (40 mm) nominal inside diameter.

C 501.2.4 Vacuum Interface Valve. A closed vacuum interface valve shall be installed to separate the piping network vacuum from atmospheric pressure. A control device shall open the vacuum interface valve where a signal is generated to remove waste from the plumbing fixture. C 501.2.5 Control Components. Where a pneumatic signal is generated at the controller, a vacuum from the

APPENDIX C

system to open the extraction valve shall be designed to operate where vacuum pressure exists to remove the accumulated waste. Each tank shall incorporate a level indicator switch that automatically controls the discharge pump and warns of malfunction or blockage as follows:

(1) Start discharge.

(2) Stop discharge.

(3) Activate an audible alarm where the level of effluent is usually high.

(4) Warning of system shutdown where the tank is full.

C 501.3 Fixtures. Fixtures utilized in a vacuum waste drainage system shall be in accordance with referenced standards listed in Chapter 17. Components shall be of corrosion resistant materials. The water closet outlet shall be able to pass a 1 inch (25.4 mm) diameter ball and shall have a smooth, impervious surface. The waste outlet and passages shall be free of obstructions, recesses, or chambers that are capable of permitting fouling. The mechanical valve and its seat shall be of such materials and design to provide a leakfree connection where at atmospheric pressure or under vacuum. The flushing mechanism shall be so designed as to ensure proper cleansing of the interior surfaces during the flushing cycle at a minimum operating flow rate. Mechanical seal mechanisms shall withdraw completely from the path of the waste discharge during the flushing operation. Each mechanical seal vacuum water closet shall be equipped with a listed vacuum breaker. The vacuum breaker shall be mounted with the critical level or marking not less than 1 inch (25.4 mm) above the flood-level rim of the fixture. Vacuum breakers shall be installed on the discharge side of the last control valve in the potable water supply line and shall be located to be protected from physical damage and contamination. C 501.4 Drainage Fixture Units. Drainage fixture units shall be determined by the manufacturer’s instructions. The pump discharge load from the collector tanks shall be in accordance with this appendix. C 501.5 Water Supply Fixture Units. Water supply fixture units shall be determined by the manufacturer’s instructions.

C 501.6 Materials. Materials used for water distribution pipe and fittings shall be in accordance with Table 604.1. Materials used for aboveground drainage shall be in accordance with Table 701.2 and shall have a smooth bore, and be constructed of non-porous material. C 501.7 Traps and Cleanouts. Traps and cleanouts shall be installed in accordance with Chapter 7 and Chapter 10. C 501.8 Testing. The entire vacuum waste system shall be subjected to a vacuum test of 29 inches of mercury (98 kPa) or not less than the working pressure of the system for 30 minutes. The system shall be gastight and watertight at all points. Verification of test results shall be submitted to the Authority Having Jurisdiction.

C 501.9 Manufacturer’s Instructions. Manufacturer’s instructions shall be provided to provide information regarding safe and proper operating instructions whether or not as part of the condition of listing to determine compliance. Such instructions shall be submitted and approved by the Authority Having Jurisdiction.

C 601.0 Single-Stack Vent System. C 601.1 Where Permitted. Single-stack venting shall be designed by a registered design professional as an engineered design. A drainage stack shall be permitted to serve as a single-stack vent system where sized and installed in accordance with Section C 601.2 through Section C 601.10. The drainage stack and branch piping in a single-stack vent system shall provide for the flow of liquids, solids, and air without exceeding the pressure differential described in Section 901.3. C 601.2 Stack Size. Drainage stacks shall be sized in accordance with Table C 601.2. Not more than two water closets shall be permitted to discharge to a 3 inch (80 mm) stack. Stacks shall be uniformly sized based on the total connected drainage fixture unit load, with no reductions in size. C 601.2.1 Stack Vent. The drainage stack vent shall have a stack vent of the same size terminating to the outdoors. C 601.3 Branch Size. Horizontal branches connecting to a single-stack vent system shall be sized in accordance with Table 703.2.

Exceptions:

(1) Not more than one water closet within 18 inches (457 mm) of the stack horizontally shall be permitted on a 3 inch (80 mm) horizontal branch.

(2) A water closet within 18 inches (457 mm) of a stack horizontally and one other fixture with up to 1 [1] ⁄ 2 inch (40 mm) fixture drain size shall be permitted on a 3 inch (80 mm) horizontal branch where connected to the stack through a sanitary tee. C 601.4 Length of Horizontal Branches. Water closets shall be not more than 4 feet (1219 mm) horizontally from the stack.

Exception: Water closets shall be permitted to be up to 8 feet (2438 mm) horizontally from the stack where connected to the stack through a sanitary tee.

C 601.4.1 Other Fixtures. Fixtures other than water closets shall be not more than 12 feet (3658 mm) horizontally from the stack. C 601.4.2 Length of Vertical Piping. The length of vertical piping from a fixture trap to a horizontal branch shall not be considered in computing the fixture’s horizontal distance from the stack.

C 601.5 Maximum Vertical Drops from Fixtures. Vertical drops from fixture traps to horizontal branch piping shall be one size larger than the trap size, but not less than 2 inches (50 mm) in diameter. Vertical drops shall be 4 feet (1219 mm) maximum length. Fixture drains that are not increased in size, or have a vertical drop exceeding 4 feet (1219 mm) shall be individually vented. C 601.6 Additional Venting Required. Additional venting shall be provided where more than one water closet is on a horizontal branch and where the distance from a fixture trap to the stack exceeds the limits in Section C 601.4. Where additional venting is required, the fixture(s) shall be vented by one of the methods described in Section 908.0 through Section 911.5. The dry vent extensions for the additional venting shall connect to a branch vent, vent stack, stack vent, or be extended outdoors and terminate to the open air.

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APPENDIX C

TABLE C 601.2 SINGLE STACK SIZE*
MAXIMUM CONNECTED DRAINAGE FIXTURE UNITS
STACK SIZE (inches)	STACKS LESS THAN 75 FEET IN HEIGHT	STACK 75 FEET TO LESS THAN 160 FEET IN HEIGHT	STACK 160 FEET OR GREATER IN HEIGHT
3	24	NP	NP
4	225	24	NP
5	480	225	24
6	1015	480	225
8	2320	1015	480
10	4500	2320	1015
12	8100	4500	2320
15	13 600	8100	4500

For SI units: 1 inch = 25 mm, 1 foot = 304.8 mm

NP = Not permitted

C 601.7 Stack Offsets. Where there are no fixture drain connections below a horizontal offset in a stack, the offset does not need to be vented. Where there are fixture drain connections below a horizontal offset in a stack, the offset shall be vented. There shall be no fixture connections to a stack within 2 feet (610 mm) above and below a horizontal offset.

C 601.8 Prohibited Connections Near Base of Stack. Where stacks are more than 75 feet (22 860 mm) high, a separate stack shall be provided for the fixtures on the lower two stories. The stack for the lower two stories shall be permitted to be connected to the branch of the building drain that serves the stack for the upper stories at a point that is not less than 8 feet (2438 mm) downstream from the base of the upper stack. Where stacks are less than 75 feet (22 860 mm) high but more than two stories high, the lowest story shall not connect within 8 feet (2438 mm) downstream from the base of the stack. Venting for the lowest story shall be provided in accordance with Section C 601.8.1 and Section C 601.8.2.

C 601.8.1 Conditional Vent. Venting of fixtures on the lowest floor shall be in accordance with Section 908.0 through Section 911.5 and may connect into the single-stack as a conditional vent. The conditional vent connects into the stack by means of a wye-fitting to prevent ingress of drainage into the vent. No more than 12 drainage fixture units (DFU) may be connected into the conditional vent and shall connect not less than 8 feet (2438 mm) above the stack base.

C 601.8.2 Other Branch Vent. Other branch vents shall be vented in accordance with Section 908.0 through Section 911.5.

C 601.9 Sizing Building Drains and Sewers. In a single-stack vent system, the building drain and branches thereof shall be sized in accordance with Table 703.2, and the building sewer shall be sized in accordance with Table 717.1. C 601.10 Parallel Vent Stacks. Drainage stacks extending more than 75 feet (22 860 mm) shall be provided with a parallel vent stack and shall meet the requirements of Section 907.0.

394 2025 CALIFORNIA PLUMBING CODE

CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE