Workers' Compensation Insurance: FAQs for California plumbers

Yes, if you have even one employee. California law requires every employer with one or more employees to carry workers' compensation insurance (Labor Code §3700). That applies the day you hire your first apprentice, helper or office person, whether they are full-time, part-time or seasonal, and whether your company is a sole proprietorship, partnership, corporation or LLC.

If you are a C-36 licensee with no employees at all, the law does not currently require a policy. You can keep your license active by filing a workers' compensation exemption with CSLB certifying that you have no employees. Two cautions: the exemption is not available if your license is qualified by a responsible managing employee (RME), and it becomes invalid the moment you hire someone subject to California workers' compensation law. CSLB must receive proof of coverage within 90 days of that hire.

The exemption also has an end date. Under SB 216, as amended by SB 1455, every licensed contractor will be required to carry workers' compensation whether or not they have employees starting January 1, 2028. Five classifications (C-8, C-20, C-22, C-39 and C-61/D-49) have already been under that rule since 2023; C-36 is not one of them yet.

Separately from the law, general contractors, property managers and public owners routinely require a certificate of workers' compensation before you can work on their jobs, even from a one-person shop. In practice, most working plumbers end up needing a policy for contract reasons before the 2028 deadline reaches them.

Only if you have no employees and you file an exemption. CSLB requires every active license to have one of two things on file: a certificate of workers' compensation insurance, or a certification of exemption stating that the licensee has no employees. A C-36 license with neither is subject to suspension.

The exemption is available to a C-36 plumbing contractor who truly has no employees, with limits:

• It is not available if the license is qualified by an RME, because an RME is by definition an employee.
• It is not available to the five classifications that SB 216 brought under a universal requirement in 2023 (C-8, C-20, C-22, C-39 and C-61/D-49). A C-36 that also holds one of those classifications must carry coverage.
• It stops being valid the moment you hire anyone subject to California workers' compensation law. CSLB must receive proof of coverage within 90 days of that hire, and operating with an invalid exemption exposes you to both license discipline and the state's uninsured-employer penalties.

Keep in mind the exemption is a licensing document, not a shield. If an investigator or a claimant shows you had workers on the job, the exemption does not change the fact that you were an uninsured employer under the Labor Code.

Finally, the exemption route closes for everyone on January 1, 2028, when SB 1455's universal requirement takes effect. If you plan to still be licensed then, budget for a policy regardless of headcount.

Class code 5183 is the California workers' compensation classification for plumbing work, and it is one half of a dual-wage pair with code 5187. The Workers' Compensation Insurance Rating Bureau of California (WCIRB) assigns each plumbing employee's payroll to one code or the other based on the employee's regular hourly wage measured against a threshold WCIRB sets. Payroll for plumbers paid below the threshold goes to 5183; payroll for plumbers paid at or above it goes to 5187, which carries a lower rate per $100 of payroll.

The threshold is $35 per hour for policies effective on or after September 1, 2026 (approved by the Insurance Commissioner on May 15, 2026). It was $32 for policies effective September 1, 2024 through August 31, 2026, and WCIRB adjusts it periodically, so use the figure for your policy's effective date.

Two things matter in practice:

• The split is documented or it does not exist. The regular hourly wage and hours worked must be verifiable from payroll and time records. Payroll you cannot document is assigned to 5183, the higher-rated code, at audit.
• Not everyone on your payroll belongs in 5183 or 5187. Office staff whose duties fit code 8810 (clerical) and estimators or salespeople who fit 8742 (outside sales) can be rated separately, at much lower rates, if their duties and your records support it. Someone who answers phones in the morning and runs calls in the afternoon is plumbing payroll.

Your premium starts from three numbers: payroll, a rate per $100 of payroll for each classification, and your experience modification (X-Mod), if you have one.

Payroll ÷ 100 × classification rate × X-Mod = modified premium

Payroll is split by classification. For a plumbing company that usually means 5183 and 5187 (plumbing, split by hourly wage), and possibly 8810 (clerical) and 8742 (outside sales) for employees whose duties and records qualify. Each classification has its own rate, and the plumbing codes are rated far higher than the office codes, so where payroll lands matters as much as how much there is.

The rate is set by your insurance carrier, not by the state. Carriers in California file their own rates, and two carriers can quote the same payroll at different prices for the same classification.

The X-Mod is published by WCIRB and multiplies the whole plumbing premium. Below 1.00 it is a discount; above 1.00 it is a surcharge. Smaller companies whose expected losses fall under WCIRB's eligibility threshold have no mod and are charged at the carrier's base rate.

After that, the carrier may apply adjustments that vary by company: scheduled credits or debits based on underwriting judgment, a policy minimum premium, an expense constant, and state-mandated assessments and surcharges that are collected with the premium. The figure on your policy is an estimate based on the payroll you projected; the final premium is set at audit after the policy year ends.

Your X-Mod is a multiplier applied to your workers' compensation premium, so it moves the premium by the same percentage it sits away from 1.00. A mod of 1.25 raises your premium about 25 percent; a mod of 0.80 lowers it about 20 percent. Because workers' compensation is usually the largest insurance bill a plumbing company pays, the mod has a bigger dollar effect than any other single line on the policy.

The number is published by the Workers' Compensation Insurance Rating Bureau of California (WCIRB), a licensed rating organization, and it follows you from carrier to carrier. Your insurer applies it; neither your insurer nor your broker can change it. It compares your company's actual reported losses to the losses WCIRB expected from a company with your payroll in your classifications over a three-year experience period.

Not every plumbing company has one. WCIRB experience-rates an employer only when its expected losses over the experience period reach an eligibility threshold that is adjusted annually ($10,400 for ratings effective September 1, 2024). A one- or two-person shop is typically below that and pays the carrier's base rate.

The mod has a second cost that does not show on the invoice. Many general contractors, property managers and public owners set an X-Mod ceiling on their prequalification forms, often 1.00 or 1.25. That is a contract requirement, not California law, but a mod above the ceiling means you cannot bid the job regardless of price.

WCIRB calculates your X-Mod by dividing your company's actual losses by its expected losses over a three-year experience period.

Experience Modification = Actual Losses ÷ Expected Losses

Expected losses are projected from your reported payroll in each classification, multiplied by WCIRB's expected loss rate for that classification. Plumbing payroll in 5183 and 5187 carries a much higher expected loss rate than clerical (8810) or outside sales (8742), so the payroll split changes the denominator.

Actual losses are the claims your insurers reported to WCIRB for the policies in the experience period, valued as of the unit statistical report, which is due no later than one month before the mod takes effect.

The experience period is three policy years, beginning four years and nine months before the rating effective date and ending one year and nine months before it. The policy year that just ended is not in your mod; the three before it are.

Not every dollar counts the same. Each claim is split at a primary threshold that varies with employer size (more than ninety values, from $4,500 to $75,000). The portion below the threshold counts in full; the portion above it carries no weight under the current California plan. The first $250 of every claim is also removed. The result: claim frequency drives a plumbing company's mod more than the size of any one claim.

You are rated only if your expected losses over the period reach WCIRB's eligibility threshold, adjusted annually ($10,400 for ratings effective September 1, 2024).

Three rating years. A claim belongs to the policy year in which the injury happened, and that policy year sits in three consecutive X-Mods before it rolls off.

The timing is what surprises most contractors. The experience period runs from four years and nine months before the mod's effective date to one year and nine months before it, which means the policy year that just ended is not in your mod yet. An injury this year first appears in the mod that takes effect one to two years from now, depending on where in your policy year the injury occurs, and stays for the three mods that include that policy year. A claim affects your premium for three years, but those years start after a delay, not on the day of the injury.

The value that counts is the value your insurer reports to WCIRB on the unit statistical report. The first report is generally valued about eighteen months after the policy began, with annual updates after that. A claim that is open and reserved high on the valuation date is in the mod at that figure; if it later closes for less, the lower value appears in the next mod, not the current one.

Two consequences. The "good year" you just had will not help until the mod after next. And the window to influence a claim's reported value is before the valuation date, working with the adjuster on return-to-work, closure and reserve accuracy, not after the mod arrives.

Yes, but only in specific situations. Under WCIRB's Experience Rating Plan, an issued X-Mod is revised when:

• a claim in the experience period is declared non-compensable (denied);
• a subrogation recovery is reported, meaning a third party reimbursed the carrier for some of the claim;
• a material change in ownership is identified that should have changed which history follows the company; or
• payroll is reclassified after an inspection, for example when a carrier's inspector finds that office or sales payroll was reported as plumbing payroll, or the reverse.

A modest change in a claim's value does not usually revise an issued mod; the new value flows into the next year's mod through the next unit statistical report. There is one value-based exception in California law: if the claims used in the mod are closed and their combined value falls below 60 percent of the highest combined value previously reported for them, Insurance Code section 11751.9 requires the mod to be revised using the current values. Either way, the better fix for a reserve that looks too high is to work the claim with the adjuster before the valuation date.

If one of the listed situations applies, the correction runs through your insurer, which reports the corrected data to WCIRB; WCIRB then reissues the mod. Your broker's job is to find the error. Start with the rating worksheet, which lists every policy year, the payroll by classification and every claim with its reported value, and compare it line by line to your loss runs and payroll reports. Classification and payroll errors are the most common and the most correctable.

Two things happen at once: you become an uninsured employer under the Labor Code, and your CSLB license becomes subject to suspension. Both start on the cancellation date, not when you notice.

Licensing. CSLB requires an active license to have a certificate of workers' compensation insurance (or a valid no-employee exemption) on file. Failure to maintain required coverage results in license suspension, and work performed while suspended is unlicensed work. Under B&P §7031, a contractor not properly licensed at all times during a job generally cannot sue to collect for it, and the customer may sue to recover what they paid. Treat a lapse as a shutdown, not a paperwork problem.

The Labor Code. If employees work during the gap, you are exposed to the state's uninsured-employer penalties: a misdemeanor under Labor Code §3700.5 (fine of at least $10,000 and/or up to a year in county jail), a stop order barring you from using employee labor until coverage is in place, and a civil penalty of the greater of twice the premium you should have paid or $1,500 per employee. If someone is hurt during the gap, you pay the injury costs yourself and can be sued civilly.

What to do. If cancellation was for non-payment, call the carrier or your producer immediately; reinstatement without a lapse may still be possible. If not, replacement coverage must be bound and a new certificate sent to CSLB before your crew works another day.

Operating with employees and no workers' compensation coverage is a crime in California, and the penalties stack. From the Department of Industrial Relations:

• Misdemeanor (Labor Code §3700.5): a fine of not less than $10,000 and/or up to one year in county jail.
• Stop order: the Division of Labor Standards Enforcement can bar you from using employee labor until coverage is obtained. Violating a stop order is a separate misdemeanor (up to 60 days in jail, up to a $10,000 fine).
• Civil penalty (§3722(b)): the greater of twice the premium you would have paid during the uninsured period or $1,500 per employee.
• If an injured worker's claim reaches the Workers' Compensation Appeals Board: $10,000 per payroll employee for a compensable injury or $2,000 per employee for a non-compensable one, up to $100,000. You also pay the injured worker's benefits directly, and the worker can sue you in civil court, where the usual workers' compensation limits on damages do not protect you.

The Uninsured Employers Benefits Trust Fund pays benefits to the injured worker when the employer cannot, then pursues the employer for reimbursement.

Licensing consequences come on top. CSLB suspends the license of a contractor who fails to maintain required coverage, work done while suspended is unlicensed work, and an unlicensed contractor generally cannot sue to be paid for it. For a plumbing company, the realistic exposure from one serious trench injury without coverage is the business itself.

A premium audit is the carrier's review of your actual payroll and operations after the policy year ends, used to replace the estimated premium you were charged with the final premium you owe. It is a contract provision of every workers' compensation policy, not a government inspection, and it can produce a bill or a refund.

The auditor checks three things: how much payroll you had, which classification each dollar belongs in, and whether anyone paid as a subcontractor should have been charged as an employee. Expect to be asked for:

• Payroll records for the policy period, by employee, with hourly wage and hours worked
• Quarterly payroll tax filings (federal 941s and California DE 9 / DE 9C) to reconcile totals
• Time records supporting any dual-wage split between 5183 and 5187 and any clerical (8810) or outside sales (8742) assignment
• Job descriptions for anyone classified outside the plumbing codes
• 1099s, the general ledger and cash disbursements, to identify payments to subcontractors and casual labor
• Certificates of insurance for every subcontractor, showing their own workers' compensation coverage

Where the money moves for plumbing companies: payroll that cannot be documented at or above the dual-wage threshold is assigned to 5183, the higher-rated code; "clerical" employees who also run calls are moved to plumbing payroll; and subcontractors without a certificate are generally charged as if they were your employees. Good records are the entire defense: keep hours and wage rates by employee, and collect sub certificates before the work starts.

Often, yes. Paying someone on a 1099 does not by itself make them a subcontractor for workers' compensation purposes; what matters is whether they hold their own contractor's license and carry their own coverage.

Unlicensed "subs." Under Labor Code §2750.5, as it is generally applied, a worker performing services that require a contractor's license is presumed to be an employee, and a person who does not hold the required license cannot qualify as an independent contractor for that work. In practice, the unlicensed helper you pay by the job, and the workers of an unlicensed outfit you bring in for a repipe, are treated as your employees for workers' compensation. The carrier charges their payments as payroll at audit, and if one of them is injured, the claim is yours.

Licensed subs. A properly licensed subcontractor who carries their own workers' compensation is responsible for their own employees. You prove that with a certificate of insurance showing coverage in force while they worked for you. Without a certificate, carriers generally charge the subcontract cost (or the labor portion of it) as your payroll at audit, because they treat the exposure as uninsured. A licensed sub with a valid no-employee exemption is a gray area; ask your carrier how it handles that at audit before you rely on it.

Two habits prevent most audit surprises: verify the license and collect the certificate before the sub starts, and keep the certificates with your audit file.

On January 1, 2028, every licensed California contractor, including a C-36 plumber with no employees, will be required to carry workers' compensation insurance as a condition of holding an active license. The no-employee exemption that sole operators rely on today goes away.

Here is how it got there. SB 216 (2022) did two things: it required five classifications (C-8 concrete, C-20 HVAC, C-22 asbestos abatement, C-39 roofing and C-61/D-49 tree service) to carry coverage from January 1, 2023 whether or not they had employees, and it set a date of January 1, 2026 for the same rule to reach all other classifications. SB 1455 (2024) postponed that universal date by two years, to January 1, 2028. Until then, a C-36 with no employees may still file the exemption with CSLB.

For a one-person plumbing shop, the practical effects are:

• You will need a policy in force, and a certificate on file with CSLB, to keep the license active after the deadline. Expect CSLB to publish filing details closer to the date; the renewal mechanics are CSLB's to set.
• Because a no-employee policy is rated on the owner's exposure rather than a crew's payroll, the carrier market for these policies is still taking shape. Talk to your producer well ahead of your first renewal after the deadline.
• Nothing about 2028 changes the rule that applies today: hire one employee and coverage is required immediately.

Watch for further legislation; the date has already moved once.

There is no single answer, because the premium is built from your own numbers: your payroll, how it is classified, your carrier's rate for each classification and, if you are experience rated, your X-Mod. Two plumbing companies with the same number of trucks can pay very different premiums.

What moves the cost, roughly in order of weight:

1. Plumbing payroll. Premium is charged per $100 of payroll, so the size of your field crew is the base.
2. Classification split. Plumbers paid at or above WCIRB's dual-wage threshold are rated in 5187 at a lower rate than 5183. Office staff who qualify for 8810 and outside sales who qualify for 8742 are rated far lower still. Each split must be supported by time and payroll records or it is lost at audit.
3. Your X-Mod. Above 1.00 it surcharges the whole plumbing premium; below 1.00 it discounts it. Claim frequency drives it more than any single large claim.
4. Carrier rate and appetite. California carriers file their own rates, and one that wants plumbing accounts prices them differently than one that does not. Quote more than one market.
5. Underwriting credits and debits. Years in business, a written safety program, return-to-work practices and the mix of service versus new construction or underground work influence scheduled credits.
6. Subcontractor exposure. Uninsured or unlicensed subs are charged as your payroll at audit.

The policy premium is an estimate; the final figure comes from the audit. A quote built on your actual payroll by employee and classification is the way to a real number.