Workers' Compensation Payroll Classifications for Plumbing Contractors

The short version

Workers' compensation premium is payroll multiplied by a rate, and the rate depends on the classification the payroll is assigned to. For a California plumbing company, almost every dollar of payroll lands in one of four places: 5183 or 5187 (the plumbing pair, split by hourly wage), 8810 (clerical office employees) or 8742 (outside salespersons). The gap between the plumbing rates and the clerical rate is wide, and the gap between 5183 and 5187 is meaningful on its own, so classification is where a plumbing company's premium is decided, more than by the carrier it picks.

The classification rules are written by the Workers' Compensation Insurance Rating Bureau (WCIRB) in the California Workers' Compensation Uniform Statistical Reporting Plan (USRP), approved by the Insurance Commissioner and applied by insurers to California policies. They are not negotiable, but they are predictable: an employee's duties and documented wage determine the code, and the records you keep determine whether the auditor can apply the code you expected.

A realistic scenario

A plumbing company in Sacramento runs nine people: six field plumbers, an apprentice, an office manager who handles billing and permits, and the owner, who estimates, sells and works in the field when a crew is short. Four of the plumbers are journeymen paid $38 to $44 an hour; the other two and the apprentice are paid between $22 and $30. The owner sets up the policy with all nine in 5183 because that was the code on the application and nobody asked a follow-up question.

At the first audit, the auditor asks for the payroll register, time records and job descriptions. The office manager's duties qualify for 8810, and her payroll moves to the clerical rate. The four journeymen are paid above the dual-wage threshold, so their payroll should qualify for 5187. But the company's time records are a weekly hours total per employee, with no daily start and end times, so the auditor cannot verify a regular hourly wage under the dual-wage records rule and leaves them in 5183. The owner's payroll stays in 5183 because he works in the field some days, and the rules do not allow his payroll to be split between plumbing and sales.

One correction in the company's favour, one lost to incomplete time records, and one that was never going to go the owner's way. The gap between the audited premium and what it could have been with proper records is real money, and it recurs every year the records stay the same.

The four codes

5183 and 5187: the plumbing dual-wage pair

California classifies plumbing work under a dual-wage pair. Payroll for plumbing employees whose regular hourly wage is below the WCIRB threshold goes to 5183; payroll for employees paid at or above the threshold goes to 5187, which carries the lower rate. WCIRB rates the two halves of the pair separately, so the same plumbing work carries a different rate depending on which side of the threshold the wage falls.

The threshold is set by WCIRB and changes. For policies effective on or after September 1, 2024 it was $32 per hour (it had been $31 for policies effective September 1, 2022 and 2023, and $28 before that), and it stayed at $32 for September 1, 2025. For policies effective on or after September 1, 2026 it is $35 per hour, under the rating rules the Insurance Commissioner approved for that date. WCIRB reviews the threshold periodically, so confirm the figure for your own policy date with your broker. The threshold that counts is the one in effect for your policy's effective date, not the one in effect when the work is done.

The plumbing phraseology, 5183(1)/5187(1), covers plumbing "including shop, yard or storage operations": installation, service and repair of plumbing systems within the property line, including piping, valves, fixtures, water heaters, drain clearing in pipe up to 6 inches in diameter, related excavation by the same employer and solar water heating. Refrigeration equipment and heating or air conditioning equipment are separate subclassifications of the same pair, 5183(2)/5187(2) and 5183(3)/5187(3). The phraseology also sends some work elsewhere: street water, gas and sewer mains to the 6315/6316 and 6307/6308 pairs, sewer lines over 6 inches within the property line to 6307/6308 (and their cleaning to 9402), water softening and filtration systems to 9519, and fire sprinkler systems to 5185/5186. If your company does any of that, or duct work, electrical hookups or anything else that may sit outside the plumbing classification, raise it with your broker before the policy is written rather than letting the auditor decide.

8810: clerical office employees

8810 is for employees whose duties are confined to keeping the books, records or cash of the employer, plus correspondence and general office work (billing, payroll, answering phones, filing permits, scheduling), and who work exclusively in areas separated from all other work places of the employer by buildings, floors, partitions, railings or counters. It is one of the standard exception classifications. It is available to a plumbing company because the plumbing phraseology does not itself include clerical employees, and the employee's duties and workspace must fit.

The test is duties plus location, and both matter. A dispatcher at a desk in the warehouse next to the material racks may not qualify; an office manager who helps load a truck once a week has a problem. An employee exposed to operative hazards has their entire payroll assigned to the highest-rated classification of work they are exposed to, not just the hours spent outside the office. The rules do allow a few incidental tasks without losing the classification: depositing funds at the bank, picking up or delivering mail, buying office supplies, and entering the shop or yard to get to the office or to deliver paychecks.

8742: salespersons, outside

8742 covers employees engaged exclusively in sales, collection or public relations work away from the employer's premises (estimators and salespeople who visit customers, measure, write proposals and close jobs). An employee who splits time between outside sales and clerical work in a separated office can still qualify. It is also a standard exception. An estimator who sells a repipe and then works with the crew for a day is not an outside salesperson for classification purposes; that payroll goes to the plumbing code. Whether supervising field work without performing it disqualifies an estimator is a fact question for the auditor, so keep sales staff out of crew supervision if you want the classification to hold.

Owners and officers

Owners, partners, LLC members and corporate officers covered by the policy are classified by what they actually do. An owner in the field is plumbing payroll; one who never leaves the office may qualify for 8810. California applies minimum and maximum annual payroll amounts to covered executive officers, partners, individual employers and LLC members: for policies effective on or after September 1, 2026, a minimum of $66,300 and a maximum of $171,600 (WCIRB adjusts both each year). Some owners and officers can choose to be included in or excluded from coverage depending on the entity type; the rules differ by entity, so confirm the options with a licensed producer before the policy is bound.

What can and cannot be split

This is where most plumbing companies misunderstand the system. Three rules do most of the work.

Standard exceptions cannot share an employee. The USRP does not permit one employee's payroll to be divided, within a policy period, between a standard exception and any other classification; the only exception is a single permanent job reassignment. An employee who does both clerical work and plumbing work is assigned entirely to the plumbing classification. There is no proration for the office half of the week.

The dual-wage split is by employee and wage, not by job or time. Each plumbing employee is assigned to 5183 or 5187 based on their regular hourly wage. You do not split one employee's payroll between the two codes because some jobs are harder than others.

Division by time, where it is allowed at all, requires specific time records. Where an employee works in two separately classified operations that are not standard exceptions, the USRP permits a split only if complete and accurate payroll records with supporting time records show the work separately; payroll may not be divided by percentages, averages or estimates. Without those records the entire payroll goes to the highest-rated classification that applies to any part of the employee's work. Construction classifications carry their own, similar records requirements, and no division is allowed where a classification's phraseology prohibits it.

A table makes the practical effect clear:

These outcomes are general statements of how the rules are applied. The auditor's determination rests on your specific records and duties.

What counts as payroll

Classification tells you which rate applies; remuneration rules tell you what it is applied to. In general terms, remuneration includes wages, salaries, commissions, bonuses, piece-rate pay, and holiday, vacation and sick pay. Overtime counts only at its straight-time portion. WCIRB's rules exclude the overtime excess (the increase above the regular hourly wage), tips, severance pay (except accrued vacation, sick pay, commissions and bonuses) and, unless the classification says otherwise or they are provided in lieu of wages, meals and lodging. Ask your insurer how it treats per diem and tool allowances before assuming they are excluded. For a company running evening and weekend service calls, the overtime exclusion is worth real money, and in practice an auditor can only exclude what the payroll register shows separately from straight time.

Records that make the classification stick

The auditor does not take your word for anything, and the rules do not let them. The records that support each classification:

• Payroll register by employee, by pay period, showing gross wages and, separately, overtime premium.
• Time records (original time cards, time clock exports, or a field app) for every hourly field employee, showing the operations performed, total hours each day and the start and end time of each work period. That is what the dual-wage rule requires to verify a regular hourly wage. For salaried field staff, keep the same records unless your insurer confirms it audits salaries another way.
• Job descriptions for every 8810 and 8742 employee, dated and signed, describing where they work and what they do not do.
• An actual separate office for clerical staff.
• Quarterly tax filings (federal Form 941 and California DE 9 and DE 9C) to tie the register to a reported total.
• Certificates of insurance for every subcontractor paid during the period, so their cost is not charged as your payroll. Are plumbing subcontractors covered by your insurance? covers that question.

What happens at audit when the records are missing

The rules resolve every gap against the employer. Payroll whose hourly wage cannot be reconciled to original time records or a collective bargaining agreement goes to 5183. An 8810 or 8742 employee without a job description and a separate workspace, or with any evidence of field work, goes to the plumbing code. Overtime not shown separately is charged at full value. A subcontractor with no certificate is treated as your payroll. None of this is the auditor being difficult; it is how the USRP is written. How to prepare for a workers' compensation premium audit walks through the audit itself.

The consequence runs past the premium. Payroll by classification is reported to WCIRB on the unit statistical report and becomes the expected-losses side of your X-Mod, so a classification error in one year distorts your mod for the three years that policy year sits in the experience period. Seven common issues to review in a plumbing contractor's X-Mod covers which of those errors can be corrected after the fact. For the coverage itself, see Workers' compensation insurance for California plumbing companies.

Practical takeaway

1. Write down every employee's classification before the policy is bound, with the reason: wage, duties, workspace.
2. Put every field employee on a time system that records start and end times by day, and keep it for salaried field staff too.
3. Separate overtime premium on the payroll register.
4. Give every clerical and sales employee a dated job description and keep them out of the field entirely. A single afternoon loading trucks can cost a year of clerical rating.
5. Check the dual-wage threshold at every renewal and look at who sits just below it.
6. Collect certificates from subcontractors before paying them, not at audit time.
7. Review the audit worksheet when it arrives and dispute, with records, anything that does not match.

For the Sacramento company, the fix is mundane: daily start and end times on the journeymen's time records, a short job description for the office manager, and acceptance that the owner's payroll is plumbing payroll as long as he picks up a wrench. Done before the next audit, those three things change the audited premium and the data that feeds the mod for the next three years.

If you are setting up a policy or heading into a renewal, request a quote and send the payroll broken out the way the auditor will want to see it. A licensed producer can confirm the classifications before the policy is written rather than after the audit.