C-36 — Plumbing

A C-36 Plumbing Contractor license is the California specialty license that lets you legally bid, contract for, and perform plumbing work — water supply, drainage, gas piping, and water-heating systems — in any structure statewide, for pay, above the state’s $1,000 minor-work threshold. It’s issued by the Contractors State License Board (CSLB) under California Code of Regulations, Title 16, §832.36, and it’s the classification nearly every residential and commercial plumbing company in California is built around.

What a C-36 License Actually Covers

Per 16 CCR §832.36, the C-36 scope runs from the utility meter to the fixture and back out to the sewer or septic connection. In practice, that means a C-36 contractor can legally perform work such as:

• Water and gas service lines — running supply piping from the property owner’s side of the utility meter into the structure, including sizing and material selection under the California Plumbing Code.
• Drain, waste, and vent (DWV) rough-in — underground and in-wall waste piping, venting, and connection to the sewer main or an on-site septic/waste disposal system.
• Water heater and solar water-heating installs — tank, tankless, and solar thermal systems, plus the gas or electrical connections and temperature/pressure safety devices that go with them.
• Fixture trim-out — setting toilets, sinks, tubs, showers, and specialty fixtures, and connecting appliances such as dishwashers and ice makers.
• Backflow prevention and water treatment — installing, maintaining, and replacing backflow preventers, pressure-regulating valves, gas earthquake shut-off valves, and water-conditioning equipment.
• Medical, dental, and industrial gas piping — vacuum, compressed air, and medical/dental gas systems, a niche but explicitly named part of the classification.

The classification also covers ongoing maintenance and replacement of everything above — a C-36 isn’t just a new-construction license, it’s the license service and repair plumbers operate under too.

The C-36 Exam Path: What’s Actually Tested

Every CSLB applicant sits two closed-book, multiple-choice exams administered by PSI on CSLB’s behalf: the Law and Business exam (same for every classification) and the classification-specific Plumbing (C-36) trade exam. CSLB’s own C-36 License Examination Study Guide (effective for exams scheduled March 1, 2025 and later) is the only authoritative source for content weighting, and it breaks the trade exam into five sections:

• Planning and Estimating — 22% (scope/code compliance, pipe sizing and venting, shop drawings, job-site inspection, cost estimating)
• Underground and Rough Systems — 22% (excavation, underground piping layout, fuel gas piping, insulation and system testing)
• Finish Plumbing Installations — 20% (fixtures, water heaters, shut-off valves, specialty and commercial/industrial piping)
• Service, Repair, and Remodel — 19% (troubleshooting, leak isolation, repair, retrofit, disposal of plumbing materials)
• Safety — 17% (personnel, job-site, and environmental safety)

CSLB states these percentages are approximate. Candidates get 3.5 hours per exam, a calculator is provided for math-based questions, there’s no penalty for guessing, and the exam is closed-book — no code books or reference material at the testing center. CSLB does not publicly publish the exact number of questions or a numeric passing percentage for the C-36 trade exam specifically; third-party prep sites cite figures like “115 questions / 72% to pass,” but that number doesn’t appear in CSLB’s own study guide or exam FAQ, so treat it as an estimate, not a board-confirmed figure.

C-36 License Requirements, Step by Step

1. Qualify on experience. You need at least 4 years of journeyman-, foreman-, supervisor-, or contractor-level plumbing experience within the 10 years before you apply. Up to 3 of those 4 years can be credited through a plumbing apprenticeship, trade school, or a construction-related degree — but at least 1 full year has to be hands-on practical experience.
2. File the application. Submit CSLB’s Application for Original Contractor License with the $450 non-refundable application processing fee (per CSLB’s published fee schedule). Don’t send the bond or license fee yet — that comes after you pass.
3. Get fingerprinted (Live Scan). DOJ and FBI background check fees are separate (roughly $32 DOJ / $17 FBI as of CSLB’s current schedule).
4. Pass both exams. Law & Business plus the C-36 trade exam, scheduled through PSI, 3.5 hours each.
5. Post the bond and show insurance. A $25,000 contractor’s bond is required (the statewide CSLB bond amount, not C-36-specific), along with proof of workers’ compensation coverage if you have employees, or a filed CSLB workers’-comp exemption if you don’t.
6. Pay the initial license fee and get your number. $200 for a sole owner, $350 for a partnership/corporation/LLC, and CSLB issues the active C-36 license.

C-36 vs. the Classifications People Confuse It With

C-36 vs. C-4 (Boiler, Hot Water Heating and Steam Fitting). C-36 covers general water-heating equipment installs (tank, tankless, solar) as part of a broader plumbing scope. C-4 is narrower and deeper: boiler systems, hot-water heating loops, and steam fitting — the kind of work you’d see on a commercial boiler plant or a hydronic heating retrofit. If the whole job is plumbing with a water heater in the mix, C-36 is the license. If the core of the job is boiler or steam-system work, C-4 is the more precise (and sometimes legally required) classification.

C-36 vs. C-42 (Sanitation System). Both touch on-site waste disposal — 16 CCR §832.36 explicitly includes “construction and connection of on-site waste disposal systems” in the C-36 scope. C-42 exists for contractors who specialize narrowly in septic tanks, leach fields, and marine sanitation devices without doing the rest of a building’s plumbing. A full-service plumbing company installing a septic system as part of a house build operates under C-36; a dedicated septic-only outfit typically holds C-42.

C-36 vs. C-34 (Pipeline). C-34 covers pipelines that convey liquids or gases outside the building envelope — municipal water mains, cross-country pipelines, large-scale utility infrastructure. C-36 stops at the property owner’s side of the meter and works inward to the structure. A contractor extending a city water main to a subdivision boundary needs C-34; the plumber connecting each house to that main needs C-36.

Who Actually Needs a C-36 License

C-36 is the license behind residential service-and-repair plumbers, new-construction rough-in and finish plumbing crews, commercial tenant-improvement plumbing subs, and multifamily/apartment maintenance plumbing companies. Typical projects range from a single water heater swap or a re-pipe on an older home, to full rough-in and trim-out on a new subdivision, to backflow-device testing contracts for commercial property managers, to gas-line extensions for a restaurant’s new kitchen equipment. General contractors (B license) routinely subcontract plumbing scope to a C-36 rather than self-performing it — plumbing is one of the trades a B-licensed GC generally cannot do directly under CSLB’s classification rules.

C-36 Plumbing License: Frequently Asked Questions

Do I need a C-36 to just replace water heaters? Yes. Water-heating equipment installation, including solar water heating, is explicitly part of the C-36 scope under 16 CCR §832.36.

Can a C-36 install a septic system, or do I need C-42? A C-36 can install and connect on-site waste disposal systems as part of its scope. C-42 is a separate, narrower classification for contractors who work only in sanitation systems — you don’t need both unless your company operates in both lanes independently.

Does gas piping fall under C-36 or a separate license? Gas piping, gas appliances, flues, and related connections are named directly in the C-36 scope — no separate gas license is required in California for this work.

Can a General Building (B) contractor install plumbing directly? Generally no. Standalone plumbing work isn’t a “framing and structural” trade a B contractor can self-perform; it needs to be done by (or subcontracted to) a properly licensed C-36.

Is the C-36 trade exam open-book? No. CSLB’s own study guide states plainly that it’s a closed-book exam — no code books or reference material at the test center, though a calculator is provided.

How much of my required experience can come from school instead of job sites? Up to 3 of the required 4 years can come from a recognized apprenticeship, trade program, or construction-related degree, but CSLB requires at least 1 full year to be actual hands-on practical experience.

What bond does a C-36 contractor need to carry? The standard CSLB contractor’s bond of $25,000 — the same statewide amount required of nearly every active license classification, not a C-36-specific figure.

Do I need workers’ comp to get licensed? If you have employees, yes — active coverage is required before CSLB will issue the license. If you have no employees, you file a CSLB workers’-compensation exemption instead.