California Plumbing Code (CPC)

The California Plumbing Code (CPC) is Part 5 of the California Building Standards Code (Title 24, California Code of Regulations). It sets the minimum standards for the design, materials and installation of plumbing systems — water supply, drainage, waste and vent (DWV), fixtures, water heaters, fuel-gas piping and backflow protection — to safeguard public health and safety. The CPC is based on the Uniform Plumbing Code (UPC) published by IAPMO, reprinted with California-specific amendments adopted by state agencies.

The 2025 California Plumbing Code is the current edition, effective January 1, 2026 and based on the 2024 UPC, replacing the 2022 CPC. Because Title 24 is updated on a three-year cycle and local jurisdictions may add amendments, the requirements that apply to your plumbing project depend on the edition your city or county has adopted and any local changes — which is exactly what GoCodebook reconciles for you.

Two CPC questions dominate: how many fixtures a building needs, and how the drainage and vent system is sized. The first comes from the Chapter 4 fixture tables applied to the occupant load calculated under the building code; the second from drainage fixture units and the sizing tables. Getting either wrong late in design is expensive to correct.

The CPC is organized by system. Key areas include plumbing fixtures and fittings (Chapter 4), water heaters (Chapter 5), water supply and distribution including pipe sizing, materials and backflow prevention (Chapter 6), sanitary drainage (Chapter 7), vents (Chapter 9), traps and interceptors (Chapter 10), storm drainage (Chapter 11) and fuel-gas piping (Chapter 12). It also covers alternate water sources such as gray-water and recycled-water systems.

Drainage, waste and vent (DWV) design is the source of many plan-check corrections: trap arm lengths, vent sizing and distance to vent, cleanout placement and slope. On the supply side, the code requires backflow prevention and cross-connection control on hose bibbs, irrigation and other fixtures that could contaminate potable water. Ask GoCodebook for the controlling CPC section and we return the language plus citation.

California enforces strict water-efficiency limits on fixtures — maximum flush volumes for water closets and urinals and maximum flow rates for showerheads, lavatory and kitchen faucets. New construction and major remodels also intersect with the CALGreen (Part 11) water-conservation requirements, so the more stringent provision controls. Fuel-gas piping to ranges, dryers, water heaters and furnaces is regulated under CPC Chapter 12, including approved materials (Schedule 40 steel, CSST) and pipe sizing.

Most plumbing work — re-pipes, water-heater replacement, DWV alterations, gas-line extensions and new fixtures — requires a plumbing permit and inspection from the local building department. The exact triggers vary by city. See where coverage is deepest, then ask a question to get the rule for your jurisdiction.

The Building Standards Commission publishes Title 24, and the CPC reprints the UPC with amendments from California state agencies such as HCD. Cities and counties then adopt the code and may add local amendments — for example local backflow, gray-water, or all-electric reach codes that affect gas piping and water heating. That means the controlling text for a vent, trap or backflow question can differ between two neighboring jurisdictions.

GoCodebook identifies the adopted edition and local amendments for your address and returns the governing provision with a citation, so you can verify the original language quickly. A typical job also touches the California Mechanical Code (Part 4) for water-heater venting and the California Energy Code (Part 6) for hot-water and heat-pump water-heater requirements.

Plumbing fixture counts for a commercial building are set by occupancy and occupant load, and California amends the base UPC tables — which is why a national fixture-count spreadsheet can produce the wrong answer here. Fixture counts also interact with accessibility: the required number of accessible fixtures and the clearances around them come from CBC Chapter 11B.

Drainage, waste and vent sizing runs on drainage fixture units, with rules for slope, cleanout location and spacing, and vent sizing, length and connection height. Wet venting, island venting and combination waste-and-vent systems each have their own conditions, and they are the provisions most often applied incorrectly on residential remodels.

A short list of details accounts for a large share of corrections: water-heater seismic strapping and the temperature-and-pressure relief discharge line, backflow and cross-connection protection at hose bibbs, irrigation and boiler fill, gas-piping sizing and pressure testing, and expansion control on closed water systems.

California's adopted codes — including the California Plumbing Code (CPC) — are published under Title 24 and hosted on code libraries such as UpCodes (up.codes) and ICC Digital Codes from the International Code Council (ICC). Those let you read the text section by section.

GoCodebook goes further: instead of searching a code library, you ask a question and get the controlling provision for the edition and local amendments your jurisdiction adopted, with a citation to verify. See how GoCodebook compares to UpCodes and ICC.