CPC · California Plumbing Code

When is a trap required and basic trap rules

If a fixture does not have an integral trap, the California Plumbing Code requires it be connected to an approved liquid‑seal trap (one trap per fixture except limited multi‑sink allowances), with the tailpiece kept short (≤ 24 in), trap seals between 2–4 in, and certain types (S‑traps, movable‑part traps) prohibited; see **§ 1001.2**, **§ 1001.1** and **§ 1004.1** for the controlling rules .

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

A trap is required on each plumbing fixture unless the fixture has an integral trap or another specific code exception. The California Plumbing Code requires that each plumbing fixture shall be separately trapped by an approved type of liquid seal trap (§ 1001.2) and that Chapter 10 governs trap materials, design and installation (§ 1001.1) . In addition, certain trap types and installations are prohibited (see § 1004.1) .

The single most important rule: every non‑integral plumbing fixture must have its own approved liquid‑seal trap (with permitted limited exceptions) to stop sewer gas from entering the building. See § 1001.2 .

Requirements in detail

Which fixtures must be trapped

  • Each plumbing fixture must be separately trapped (unless it has an integral trap) — § 1001.2 .
  • Special notes in the same section: food‑waste disposers installed with restaurant/commercial/industrial sinks must be connected to a separate trap; each domestic clothes washer and each laundry sink must have a separate and independent trap, except a laundry sink may also receive the adjacent washer discharge — § 1001.2 .

Trap location, tailpiece limits, and multiple fixtures

  • Keep the vertical distance from the fixture outlet to the trap weir as short as practicable; tailpiece shall not exceed 24 inches (610 mm) — § 1001.2 .
  • One trap may serve up to three single‑compartment sinks or laundry sinks of the same depth or three lavatories when they are immediately adjacent, outlets are ≤ 30 inches (762 mm) apart, and the trap is centrally located where three compartments are installed — § 1001.2 .
  • Not more than one trap is permitted on a trap arm — § 1001.2 .

Prohibited traps and movable parts

  • Traps that rely on movable parts for the seal (for example bladders or check‑valves) are prohibited — § 1004.1 and § 1004.2 .
  • “S” traps, bell traps, crown‑vented traps and traps with concealed interior partitions (except corrosion‑resisting materials) are prohibited — § 1004.1 .
  • No fixture shall be double trapped; drum and bottle traps only for special conditions and as allowed by the Authority Having Jurisdiction — § 1004.1 .

Trap seal depth, materials, and sizing

  • Trap seal (liquid seal) normal range: not less than 2 inches (51 mm) and not more than 4 inches (102 mm), unless AHJ requires deeper — § 1005.1 .
  • Traps shall be self‑cleaning (except within interceptors), and materials permitted include ABS, cast‑brass, cast‑iron, lead, PP, PVC, etc., for standard fixtures — § 1003.1 .
  • Minimum and maximum trap sizes: the trap size for a given fixture must be sufficient to drain rapidly and be no less than nor more than one pipe size larger than the size given in Table 702.1; the trap must be the same size as the trap arm — § 1003.3 . See Table 702.1(1) for trap size/DFU guidance (e.g., 1‑1/4" trap = 1 DFU; 1‑1/2" = 3 DFU; 2" = 4 DFU; 3" = 6 DFU; 4" = 8 DFU) — Table 702.1(1) .

Trap arms and venting

  • Each fixture trap must be protected by a vent (unless other code provisions apply) to prevent siphonage and backpressure — § 1002.1 and related vent chapters (see § 901.2) .
  • The developed length from trap weir to vent must be within the distances set in Table 1002.2 (and never less than two times the trap‑arm diameter) — § 1002.2 and Table 1002.2 .
  • A trap arm may change direction horizontally up to 90° without a cleanout (135° allowed for 3" and larger with exception) — § 1002.3 .

Decision‑relevant dimensions and values (quick reference)

Dimension / Topic Code value Code Reference
Each non‑integral fixture must be trapped Required § 1001.2
Tailpiece maximum length 24 in (610 mm) § 1001.2
Multi‑fixture single trap limit ≤ 3 adjacent lavatories or single‑compartment sinks; outlets ≤ 30 in (762 mm) apart § 1001.2
Trap seal depth 2 in (51 mm) min — 4 in (102 mm) max (unless AHJ requires deeper) § 1005.1
Prohibited trap forms S‑traps, bell traps, crown‑vented traps; traps with movable parts § 1004.1, § 1004.2
Trap sizing guidance (DFU) Example: 1‑1/4" = 1 DFU, 1‑1/2" = 3 DFU, 2" = 4 DFU Table 702.1(1); § 1003.3
Trap arm developed length to vent See Table 1002.2 (varies by trap arm diameter) § 1002.2, Table 1002.2

Exceptions & special cases

  • Fixtures with integral traps are not subject to the separate trapping requirement in § 1001.2 .
  • Food‑waste disposers in certain commercial sinks must be on a separate trap (explicit in § 1001.2) .
  • One trap for up to three adjacent like‑depth sinks or lavatories is permitted when the outlets and central trap placement meet § 1001.2 spacing rules .
  • Building traps are generally not permitted unless required/approved by the Authority Having Jurisdiction; when used they must have a cleanout and a relieving vent/fresh‑air intake carried above grade — § 1008.1 .
  • Floor drains subject to infrequent use must have trap‑seal protection (primers) unless AHJ waives it — § 1007.1 and § 1006.1 .

If you need to rely on a non‑standard trap or device, check with the Authority Having Jurisdiction — several sections explicitly delegate exceptions and special approvals to the AHJ (for example § 1005.1, § 1008.1) .

Common mistakes

  • Installing an S‑trap or any trap that depends on movable parts — these are prohibited (§ 1004.1, § 1004.2) .
  • Exceeding the 24‑inch tailpiece limit from outlet to trap weir — tailpieces must be as short as practicable and ≤ 24 in (§ 1001.2) .
  • Double‑trapping a fixture (two traps in series) — expressly prohibited (§ 1004.1) .
  • Using a trap too large for the fixture so that the fixture discharge can’t self‑scour (Table 702.1(1) and § 1003.3 guidance) — traps should be within the size range per the code (§ 1003.3, Table 702.1(1)) .
  • Failing to vent the trap properly (vent must protect against siphonage/backpressure) — venting requirements are in § 1002.1 and Chapter 9 (see § 901.2) .

Worked example

Scenario: A small public restroom with three adjacent lavatories, each with outlets 28 inches apart center‑to‑center. Tailpieces are short and fixtures are not integral‑trap.

Apply the rules:

  1. One trap may serve up to three adjacent lavatories if the waste outlets are not more than 30 inches (762 mm) apart and the trap is centrally located — allowed by § 1001.2 . Because spacing = 28 in (< 30 in), a single centrally located trap is permitted.
  2. Ensure the tailpiece from each lavatory does not exceed 24 in (610 mm) to the trap weir — § 1001.2 .
  3. Confirm vent protection and trap‑arm developed length to the vent comply with Table 1002.2; do not exceed the allowed trap‑arm length for the trap‑arm diameter (see § 1002.2 and Table 1002.2) .
  4. Choose a trap size consistent with Table 702.1(1) and § 1003.3 so the trap drains rapidly yet does not exceed the permitted size range relative to the fixture — e.g., typical lavatory trap = 1‑1/4" (1 DFU) or 1‑1/2" (3 DFU) depending on local design; confirm with Table 702.1(1) and project DFU calculations .
  5. Verify trap seal depth 2–4 in (unless AHJ requires deeper) per § 1005.1 .

Related provisions (quick links)

  • § 1001.1 — Chapter applicability: materials, design, installation of traps and interceptors
  • § 1001.2 — Where required (main trap requirement; tailpiece, multi‑sink rules)
  • § 1002.1 / § 1002.2 / § 1002.3 — Vent protection, trap‑arm developed lengths, changes of direction
  • § 1003.1 / § 1003.3 — Trap descriptions, permitted materials, and sizing rules referencing Table 702.1
  • § 1004.1 / § 1004.2 — Prohibited traps and prohibition of movable‑part traps
  • § 1005.1 — Trap seal depth limits (2–4 in)
  • § 1006.1 / § 1007.1 — Floor drain trap construction and trap‑seal protection (primers)
  • Table 702.1(1) — Maximum DFU / trap size table (trap sizing reference)
  • Table 1002.2 — Horizontal lengths of trap arms (developed length to vent)

Code references

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

  • CPC § 1.11.0. High relevance — show source text

    1 Exception 2_||||X|X|||||||||||||||||||| |1010.2|||||||||||||||||||X|||||| |1010.3|||||||||||||||||||X|||||| |1010.4|||||||||||||||||||X|||||| |1010.5|||||||||||||||||||X|||||| |1014.1A, B, C||||||||||X|X|X|X|X|X|||||||||| |1015.5||||||||||X|X|X|X|X|X|||||||||| |1015.6||||||||||X|X|X|X|X|X||||||||||

    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.

    2025 CALIFORNIA PLUMBING CODE 193

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    194 2025 CALIFORNIA PLUMBING CODE

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    CHAPTER 10

    TRAPS AND INTERCEPTORS

    1001.0 General.

    1001.1 Applicability. This chapter shall govern the materials, design, and installation of traps and interceptors.

    1001.2 Where Required. Each plumbing fixture shall be separately trapped by an approved type of liquid seal trap. This section shall not apply to fixtures with integral traps. Not more than one trap shall be permitted on a trap arm. Food waste disposers installed with a set of restaurant, commercial, or industrial sinks shall be connected to a separate trap.

    Each domestic clothes washer and each laundry sink shall be connected to a separate and independent trap, except that a trap serving a laundry sink shall also be permitted to receive the waste from a clothes washer set adjacent to it.

    The vertical distance between a fixture outlet and the trap weir shall be as short as practicable, but in no case shall the tailpiece exceed 24 inches (610 mm) in length.

    One trap shall be permitted to serve a set of not more than three single compartment sinks or laundry sinks of the same depth or three lavatories immediately adjacent to each other and in the same room where the waste outlets are not more than 30 inches (762 mm) apart, and the trap is centrally located where three compartments are installed.

    1002.0 Traps Protected by Vent Pipes.

    1002.1 Vent Pipes. Each plumbing fixture trap, except as otherwise provided in this code, shall be protected against siphonage, backpressure, and air circulation shall be assured throughout the drainage system using a vent pipe installed in accordance with the requirements of this code.

  • CPC § 1004.2 Medium relevance — show source text

    1004.2 Movable Parts. Bladders, check valves or another type of devices with moveable parts shall be prohibited to serve as a trap.

    1005.0 Trap Seals. 1005.1 General. Each fixture trap shall have a liquid seal of not less than 2 inches (51 mm) and not more than 4 inches (102 mm), except where a deeper seal is found necessary by the Authority Having Jurisdiction. Traps shall be set true with respect to their liquid seals and, where necessary, they shall be protected from freezing.

    1006.0 Floor Drain Traps. 1006.1 General. Floor drains shall connect into a trap so constructed that it can be readily cleaned and of a size to serve efficiently the purpose for which it is intended. The drain inlet shall be so located that it is in full view. Where subject to the reverse flow of sewage or liquid waste, such drains shall be equipped with an approved backwater valve.

    1007.0 Trap Seal Protection. 1007.1 General. Floor drain or similar traps directly connected to the drainage system and subject to infrequent use shall be protected with a trap seal primer, except where not deemed necessary for safety or sanitation by the Authority Having Jurisdiction. Trap seal primers shall be accessible for maintenance.

    1007.2 Trap Seal Primers. Potable water supply trap seal primer valves shall comply with ASSE 1018. Drainage or electronic design type trap seal primer devices shall comply with ASSE 1044 or IAPMO PS 76.

    1008.0 Building Traps. 1008.1 General. Building traps shall not be installed except where required by the Authority Having Jurisdiction. Each building trap where installed shall be provided with a cleanout and with a relieving vent or fresh-air intake on the inlet side of the trap, which needs not be larger than one-half the diameter of the drain to which it connects. Such relieving vent or fresh-air intake shall be carried above grade and terminate in a screened outlet located outside the building.

    1009.0 Interceptors (Clarifiers) and Separators.

    1009.1 Where Required. Interceptors (clarifiers) (including grease, oil, sand, solid interceptors, etc.) shall be required

    by the Authority Having Jurisdiction where they are necessary for the proper handling of liquid wastes containing grease, flammable wastes, sand, solids, acid or alkaline substances, or other ingredients harmful to the building drainage system, the public or private sewer, or to public or private sewage disposal. A list of acceptable interceptor standards is referenced in Table 1009.1.

    TABLE 1009.1 APPROVED INTERCEPTORS (CLARIFIERS)

  • CPC § 1001.0 Medium relevance — show source text

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

    CHAPTER 10

    TRAPS AND INTERCEPTORS

    1001.0 General.

    1001.1 Applicability. This chapter shall govern the materials, design, and installation of traps and interceptors.

    1001.2 Where Required. Each plumbing fixture shall be separately trapped by an approved type of liquid seal trap. This section shall not apply to fixtures with integral traps. Not more than one trap shall be permitted on a trap arm. Food waste disposers installed with a set of restaurant, commercial, or industrial sinks shall be connected to a separate trap.

    Each domestic clothes washer and each laundry sink shall be connected to a separate and independent trap, except that a trap serving a laundry sink shall also be permitted to receive the waste from a clothes washer set adjacent to it.

    The vertical distance between a fixture outlet and the trap weir shall be as short as practicable, but in no case shall the tailpiece exceed 24 inches (610 mm) in length.

    One trap shall be permitted to serve a set of not more than three single compartment sinks or laundry sinks of the same depth or three lavatories immediately adjacent to each other and in the same room where the waste outlets are not more than 30 inches (762 mm) apart, and the trap is centrally located where three compartments are installed.

    1002.0 Traps Protected by Vent Pipes.

    1002.1 Vent Pipes. Each plumbing fixture trap, except as otherwise provided in this code, shall be protected against siphonage, backpressure, and air circulation shall be assured throughout the drainage system using a vent pipe installed in accordance with the requirements of this code.

    1002.2 Fixture Traps. Each fixture trap shall have a protecting vent so located that the developed length of the trap arm from the trap weir to the inner edge of the vent shall be within the distance given in Table 1002.2 but in no case less than two times the diameter of the trap arm. 1002.3 Change of Direction. A trap arm shall be permitted to change direction without the use of a cleanout where such change of direction does not exceed 90 degrees (1.57 rad). Horizontal changes in the direction of trap arms shall be in accordance with Section 706.3.

    Exception: For trap arms, 3 inches (80 mm) in diameter and larger, the change of direction shall not exceed 135 degrees (2.36 rad) without the use of a cleanout. 1002.4 Vent Pipe Opening. The vent pipe opening from soil or waste pipe, except for water closets and similar fixtures, shall not be below the weir of the trap.

    1003.0 Traps – Described. 1003.1 General Requirements. Each trap, except for traps within an interceptor or similar device shall be selfcleaning. Traps for bathtubs, showers, lavatories, sinks, laun

    dry sinks, floor drains, urinals, drinking fountains, dental units, and similar fixtures shall be of standard design, weight and shall be of ABS, cast-brass, cast-iron, lead, PP, PVC, or other approved material. An exposed and readily accessible drawn-copper alloy tubing trap, not less than 17 B & S Gauge (0.045 inch) (1.143 mm), shall be permitted to be used on fixtures discharging domestic sewage.

    Exception s :

  • CPC § 1.6 Medium relevance — show source text
    PLUMBING APPLIANCES, APPURTENANCES, OR FIXTURES MINIMUM SIZE TRAP
    AND TRAP ARM7
    (inches)    		 PRIVATE PUBLIC ASSEMBLY8
    Water Closet, greater than 1.6 GPF Gravity Tank6 3 4.0 6.0 8.0
    Water Closet, greater than 1.6 GPF Flushometer Valve6 3 4.0 6.0 8.0

    For SI units: 1 inch = 25 mm

    Notes: 1 Indirect waste receptors shall be sized based on the total drainage capacity of the fixtures that drain thereinto, in accordance with Table 702.2. 2 Provide a 2 inch (50 mm) minimum drain. 3 For refrigerators, coffee urns, water stations, and similar low demands. 4 For commercial sinks, dishwashers, and similar moderate or heavy demands. 5 Buildings having a clothes-washing area with clothes washers in a battery of three or more clothes washers shall be rated at 6 fixture units each for purposes of sizing common horizontal and vertical drainage piping. 6 Water closets shall be computed as 6 fixture units where determining septic tank sizes based on Appendix H of this code. 7 Trap sizes shall not be increased to the point where the fixture discharge is capable of being inadequate to maintain their self-scouring properties. 8 Assembly [Public Use (see Table 422.1)]. 9 For a bathtub to shower retrofit, a 1 1 / 2 inch (40 mm) trap and trap arm shall be permitted with a maximum shower size of 36 inches (914 mm) in width and 60 inches (1524 mm) in length. See Section 408.6 and Section 408.7. 10 For drainage fixture unit values related to lots within mobilehome parks in all parts of the State of California, see California Code of Regulations, Title 25, Division 1, Chapter 2, Article 5, Section 1268. For drainage fixture unit values related to lots within special occupancy parks in all parts of the State of Cal- ifornia, see California Code of Regulations, Title 25, Division 1, Chapter 2.2, Article 5, Section 2268.

    required, and the unit equivalent of fixtures and devices not shown in Table 702.1 shall be based on the size of trap or trap

    arm.

    Maximum drainage fixture units for a fixture trap and trap arm loadings for sizes up to 4 inches (100 mm) shall be in accordance with Table 702.1(1).

    TABLE 702.1(1) MAXIMUM DRAINAGE FIXTURE UNITS FOR A

    TRAP AND TRAP ARM*

    SIZE OF TRAP AND
    TRAP ARM (inches)    		 DRAINAGE FIXTURE UNIT
    VALUES (DFU)

    11⁄4    		 1 unit

    11⁄2    		 3 units

    2    		 4 units
    3 6 units


    4    		 8 units

    For SI Units: 1 inch = 25 mm

    *** Exception:** On self-service laundries.

    702.2 Intermittent Flow. Drainage fixture units for intermittent flow into the drainage system shall be computed on the rated discharge capacity in gallons per minute (gpm) (L/s) in accordance with Table 702.2.

    TABLE 702.1(1) MAXIMUM DRAINAGE FIXTURE UNITS FOR A

    TRAP AND TRAP ARM*

  • CPC § 25.4 Medium relevance — show source text

    For SI units: 1 inch = 25.4 mm

    Notes: 1 Maintain 1 ⁄ 4 inch per foot slope (20.8 mm/m). 2 The developed length between the trap of a water closet or similar fixture (measured from the face of the closet flange to the inner edge of the vent) and its vent shall not exceed 6 feet (1829 mm). 3 Horizontally wet vented bathtubs, showers and similar fixtures shall be limited to a maximum of 6 feet (1829 mm) for 1½ inch (40 mm) fixture drains and 8 feet (2438 mm) for 2 inch (50 mm) fixture drains, maintaining ¼ inch per foot slope (20.8 mm/m).

    1003.2 Slip Joint Fittings. A maximum of one approved slip joint fitting shall be permitted to be used on the outlet side of a trap, and no tubing trap shall be installed without a listed tubing trap adapter. Listed plastic trap adapters shall be permitted to be used to connect listed metal tubing traps.

    1003.3 Size. The size (nominal diameter) of a trap for a given fixture shall be sufficient to drain the fixture rapidly but in no case less than nor more than one pipe size larger than given in Table 702.1. The trap shall be the same size as the trap arm to which it is connected.

    TABLE 1002.2

    HORIZONTAL LENGTHS OF TRAP ARMS (EXCEPT FOR WATER CLOSETS AND SIMILAR FIXTURES) [1, 2, 3]

    For SI units: 1 inch = 25.4 mm

    Notes: 1 Maintain 1 ⁄ 4 inch per foot slope (20.8 mm/m). 2 The developed length between the trap of a water closet or similar fixture (measured from the face of the closet flange to the inner edge of the vent) and its vent shall not exceed 6 feet (1829 mm). 3 Horizontally wet vented bathtubs, showers and similar fixtures shall be limited to a maximum of 6 feet (1829 mm) for 1½ inch (40 mm) fixture drains and 8 feet (2438 mm) for 2 inch (50 mm) fixture drains, maintaining ¼ inch per foot slope (20.8 mm/m).

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    TRAPS AND INTERCEPTORS

    1004.0 Traps.

    1004.1 Prohibited. No form of trap that depends for its seal upon the action of movable parts shall be used. No trap that has concealed interior partitions, except those of plastic, glass, or similar corrosion-resisting material, shall be used. “S” traps, bell traps, and crown-vented traps shall be prohibited. No fixture shall be double trapped. Drum and bottle traps shall be installed for special conditions. No trap shall be installed without a vent, except as otherwise provided in this code.

    1004.2 Movable Parts. Bladders, check valves or another type of devices with moveable parts shall be prohibited to serve as a trap.

  • CPC § 101.5 Medium relevance — show source text

    B 101.5 Trap Sizes. Trap sizes are required to be equivalent to the branches they serve (two pipe sizes larger than normal), and tailpieces between fixtures or floor drains and such traps shall be reduced to normal size.

    B 101.6 Layout Drawings. Duplicate layout drawings of each such proposed piping system shall be presented to the Authority Having Jurisdiction and approval obtained before an installation is made. Complicated layouts shall be checked by qualified personnel. B 101.6.1 Example of Sizing. A floor drain normally requires a 2 inch (50 mm) trap and waste. On a combination waste and vent system, both trap and waste shall be increased two pipe sizes (through 2 [1] ⁄ 2 inches and 3 inches) (65 mm and 80 mm), which would make the trap 3 inches (80 mm). Pipe sizes recognized for this purpose are 2 inches, 2 [1] ⁄ 2 inches, 3 inches, 3 [1] ⁄ 2 inches, 4 inches, 4 [1] ⁄ 2 inches, 5 inches, 6 inches, etc. (50 mm, 65 mm, 80 mm, 90 mm, 100 mm, 115 mm, 125 mm, 150 mm, etc.). The tailpiece between the floor drain and its trap shall be 2 inches (50 mm) (or normal size) to ensure that the amount of wastewater entering the trap partially fills the waste branch. A 3 inch (80 mm) floor drain would thus require a 4 inch (100 mm) trap, and a 4 inch (100 mm) floor drain would require a 5 inch (125 mm) trap for the reasons previously stated.

    WHERE IN DOUBT, CHECK WITH YOUR LOCAL Authority Having Jurisdiction.

    2025 CALIFORNIA PLUMBING CODE 383

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    384 2025 CALIFORNIA PLUMBING CODE

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    CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE

    APPENDIX C - ALTERNATE PLUMBING SYSTEMS

    (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 § 911.3 Medium 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 § 222.0 Medium relevance — show source text

    222.0 – T –

    T Rating. The time period that the penetration firestop system, including the penetrating item, limits the maximum temperature rise of 325°F (181°C) above its initial temperature through the penetration on the nonfire side, where tested in accordance with ASTM E814 or UL 1479.

    Tailpiece. The pipe or tubing that connects the outlet of a plumbing fixture to a trap. Testing Agency. [HCD 1] See “Approved Testing Agency”. Thermostatic (Temperature Control) Valve. A mixing valve that senses outlet temperature and compensates for fluctuations in incoming hot or cold water temperatures. Toilet. [OSHPD 1, 2, 3, 4 & 5] A fixture within a toilet room which is used for defecation or urination. Toilet Facility. A room or space containing not less than one lavatory and one water closet.

    Toilet Room. [OSHPD 1, 2, 3, 4 & 5] A room within or on the premises containing water closets, urinals, and other required facilities. Transition Gas Riser. A listed or approved section or sections of pipe and fittings used to convey fuel gas and installed in a gas piping system to provide a transition from belowground to aboveground.

    Trap. A fitting or device so designed and constructed as to provide, where properly vented, a liquid seal that will prevent the back passage of air without materially affecting the flow of sewage or wastewater through it.

    Trap Arm. Those portions of a fixture drain between a trap and the vent.

    Trap Primer. A device and system of piping that maintains a water seal in a remote trap. Trap Seal. The vertical distance between the crown weir and the top dip of the trap. Crown Weir (Trap Weir). The lowest point in the cross-section of the horizontal waterway at the exit of the trap. Top Dip (of the trap). The highest point in the internal cross-section of the trap at the lowest part of the bend (inverted siphon). By contrast, the bottom dip is the lowest point in the internal cross-section. Treated Gray Water. [BSC-CG & HCD 1] Nonpotable water meeting the definition of “gray water” collected and treated on-site suitable for direct beneficial use.

    223.0 – U –

    UPC. [HCD 1] “UPC” is the latest edition of the Uniform Plumbing Code, published by the International Association of Plumbing and Mechanical Officials. Unsanitary. See Insanitary.

    User Outlet. See Station Outlet.

    2025 CALIFORNIA PLUMBING CODE 43

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    DEFINITIONS

    224.0 – V –

    Vacuum. A pressure less than that exerted by the atmosphere.

    Vacuum Breaker. See Backflow Preventer.

  • CPC § 1.11.0. Medium relevance — show source text

    Pipe sizes recognized for this purpose are 2 inches, 2 [1] ⁄ 2 inches, 3 inches, 3 [1] ⁄ 2 inches, 4 inches, 4 [1] ⁄ 2 inches, 5 inches, 6 inches, etc. (50 mm, 65 mm, 80 mm, 90 mm, 100 mm, 115 mm, 125 mm, 150 mm, etc.). The tailpiece between the floor drain and its trap shall be 2 inches (50 mm) (or normal size) to ensure that the amount of wastewater entering the trap partially fills the waste branch. A 3 inch (80 mm) floor drain would thus require a 4 inch (100 mm) trap, and a 4 inch (100 mm) floor drain would require a 5 inch (125 mm) trap for the reasons previously stated.

    WHERE IN DOUBT, CHECK WITH YOUR LOCAL Authority Having Jurisdiction.

    2025 CALIFORNIA PLUMBING CODE 383

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    384 2025 CALIFORNIA PLUMBING CODE

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    CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE

    APPENDIX C - ALTERNATE PLUMBING SYSTEMS

    (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
    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.

    2025 CALIFORNIA PLUMBING CODE 385

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  • CPC § 1.1 Medium relevance — show source text

    1(2)_||||X||||||||||||||||||||| |903.1.1||||X|X|||||||||||||||||||| |903.1.2||||X||||||||||||||||||||| |903.1.3||||||||||X||X|X|X|X|||||||||| |906.2.1||||||||||X|X|X|X|X|X||||||||||

    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.

    2025 CALIFORNIA PLUMBING CODE 187

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    188 2025 CALIFORNIA PLUMBING CODE

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    CHAPTER 9

    VENTS

    901.0 General.

    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.

  • CPC § 1101.12.2.2 Medium relevance — show source text

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

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

    206 2025 CALIFORNIA PLUMBING CODE

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    STORM DRAINAGE

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

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

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

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

    leader or conductor before it connects to the horizontal

    drain.

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

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

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

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

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

Frequently asked questions

When can one trap serve multiple fixtures?

One trap may serve up to three single‑compartment sinks or laundry sinks of the same depth, or three lavatories immediately adjacent and within 30 in (762 mm) of each other, with the trap centered — see § 1001.2 .

Are S‑traps ever allowed?

No. S‑traps are explicitly prohibited by § 1004.1; similarly, traps that rely on movable parts are prohibited (§ 1004.2) .

How deep must a trap seal be?

Trap seals must be at least 2 in (51 mm) and no more than 4 in (102 mm) unless the Authority Having Jurisdiction requires a deeper seal — § 1005.1 .

What is the maximum tailpiece length?

The tailpiece from fixture outlet to trap weir must be as short as practicable and shall not exceed 24 in (610 mm) — § 1001.2 .

Can I use a trap with a check valve or bladder to preserve the seal?

No. Devices with moveable parts (bladders, check valves, etc.) are prohibited as traps — § 1004.2 .

Who can approve alternatives or exceptions?

The Authority Having Jurisdiction (AHJ) can require deeper seals or allow special conditions (for example building traps or special interceptors); check with the local AHJ where the code defers discretion — see § 1005.1 and § 1008.1 .

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California Plumbing Code