- Plumber ≠ pipefitter. Most wage determinations list these as separate classifications at different rates. A worker who does both types of work in the same week needs two rows on the WH-347.
- Medical gas is its own problem. In many jurisdictions, medical gas piping carries a different classification or requires a separate brazing certification — and the rate may be higher than standard plumbing.
- Apprentice registration matters. An unregistered helper is not an apprentice on the certified payroll. They're a journeyman, at journeyman rates, for every hour worked.
- State forms don't go away. Filing the federal WH-347 doesn't cover California, New York, Illinois, or New Jersey. Each requires its own form, filed separately.
Where plumbing subs run into trouble
Plumbing contractors on prevailing wage jobs face a classification problem that's easy to miss if you've never done public works before. In your shop, a plumber is a plumber — they run pipe, set fixtures, test systems. On a prevailing wage job, the type of pipe determines the classification, not the worker's license.
The federal and most state wage determinations draw a line between plumber and pipefitter (sometimes called steamfitter). The distinction matters because the rates are often different — sometimes by $5–10/hour on the base rate alone, and more when fringe is included. A worker who spends Monday through Wednesday on waste and vent piping (plumber) and Thursday through Friday on natural gas piping (pipefitter) needs two rows on the WH-347, with hours allocated to each classification.
The second trap is helpers. Many non-union plumbing shops use the term "helper" for workers who aren't licensed plumbers. On a prevailing wage job, there is no "helper" classification. If the worker is in a registered apprenticeship program, they're an apprentice at the applicable apprentice rate. If they're not registered, they're performing journeyman-level work at journeyman rates — regardless of their actual skill level or what you pay them on private jobs.
Plumbing classifications on the WH-347
Classify every worker by the work performed that week, matched to the wage determination attached to your contract. Here are the most common plumbing classifications and the error that flags each one.
| Classification | Covers | Common mistake |
|---|---|---|
| Plumber (JW) | Potable water supply, waste, vent, drainage, fixture installation, backflow devices | Including gas piping hours under this classification when the wage determination has a separate pipefitter rate |
| Pipefitter / Steamfitter | Gas piping, process piping, high-pressure steam, chilled water, compressed air, welded systems | Listing pipefitter work as plumber (lower rate) — underpayment violation |
| Apprentice (by period) | Same scope as journeyman, under supervision, at the apprentice percentage of the JW rate | Wrong apprentice period. Each period (typically 1st through 5th year) has a different percentage — check the schedule. |
| Medical Gas Piping | Oxygen, nitrous oxide, medical vacuum, medical air — in hospitals and healthcare facilities | Classifying medical gas work at standard plumber rates when the determination has a higher specialty rate |
| Sprinkler Fitter | Fire suppression piping — sometimes under a separate classification from plumbing on the same project | Assuming sprinkler work is covered by the plumber classification — many wage determinations list it separately |
On a school renovation, your plumber runs DWV piping all week. Straightforward — one classification. The next week, the same worker connects gas piping to the new boiler. That week, the boiler work is pipefitter scope, at the pipefitter rate. If you report it as plumber work because "he's a plumber," you've underpaid — and signed a Statement of Compliance certifying that you didn't.
Apprentices and helpers: the classification that doesn't exist
On prevailing wage jobs, there is no "helper" classification for plumbing work. This catches non-union plumbing shops more than any other rule, because on private work, helpers are standard.
On a public works job, your options are:
- Registered apprentice — enrolled in a state-approved or federally registered apprenticeship program, with documentation on file. Paid at the apprentice percentage of the journeyman rate for their current period.
- Journeyman plumber — everyone else. If the worker is performing plumbing work and isn't in a registered program, they're a journeyman on the certified payroll, at the full journeyman prevailing wage rate.
Apprentice-to-journeyman ratios for plumbing typically run 1:1 or 1:2 (one apprentice per one or two journeymen), depending on the state and the apprenticeship standards referenced in the wage determination. Exceeding the ratio means every extra apprentice gets reclassified at journeyman rates, retroactively, for every hour worked while the ratio was exceeded.
If your crew includes anyone you'd call a helper on a private job, either enroll them in a registered apprenticeship program before the public works job starts, or budget for them at the journeyman rate. Auditors don't care what you call them — they care what rate they were paid.
Fringe benefits for plumbing contractors
Plumbing fringe packages on prevailing wage jobs typically include three to five components:
- Health and welfare — per-hour contribution to a health benefit plan
- Pension — defined benefit or defined contribution, per-hour
- Training fund — contribution to the JATC or apprenticeship training program
- Supplemental annuity — additional retirement contribution, common in UA jurisdictions
- Industry promotion fund — smaller per-hour contribution for industry development
If you pay fringe into benefit plans, each plan's per-hour contribution must meet the amount specified on the wage determination. If you pay fringe in cash (cash-in-lieu), the total cash payment must equal the total fringe obligation. If you do a mix — some into a health plan, the rest in cash — both amounts must be documented on the Statement of Compliance, and the combined total must meet the wage determination.
Where this gets complicated for plumbing subs: the fringe rates for plumber and pipefitter are often different. If you have a worker who splits the week between both classifications, the fringe calculation is different for each set of hours. Excel formulas that handle one classification don't handle two on the same worker in the same week.
State forms for plumbing contractors
The WH-347 covers federal Davis-Bacon requirements. If your project has any state or local funding — schools, water treatment plants, municipal buildings — you likely owe a state form on top of the federal one.
California: California eCPR records generally must be submitted to the DIR at least monthly, or more frequently if the contract requires it. The penalty of up to $200/day/worker under Labor Code §1775 applies to prevailing-wage underpayment, not simply a late submission. A separate §1776 penalty applies when requested records are not produced within 10 days.
New York: Electronic filing required since January 2026. The late-filing penalty is $100 per day once a filing is more than 14 days late; it is not multiplied by worker count. Classification and rate errors can separately create back-pay liability.
Illinois: Monthly filing to the IDOL, with personal liability for the business owner for late or incorrect filings.
New Jersey: Filing through the NJ Wage Hub. Ten-day deadline. Penalties up to $5,000 and 3-year debarment.
The most expensive mistakes for plumbing subs
These are the violations that cost plumbing contractors the most money on prevailing wage audits:
- Paying helpers at helper rates. There's no helper classification on prevailing wage. Every hour a "helper" worked at less than the journeyman or registered-apprentice rate is an underpayment. Back wages plus penalties.
- Plumber/pipefitter classification errors. Gas piping reported under plumber classification when the wage determination has a separate — and higher — pipefitter rate. Back wages for every hour misclassified.
- Unregistered apprentices. If the apprentice isn't in a registered program, they're a journeyman for certified payroll purposes. You owe the full journeyman rate retroactively.
- Missing the split week. A plumber who works on DWV piping Monday through Wednesday and gas piping Thursday through Friday needs two rows. One row averaging the hours is a misclassification.
- Fringe shortfalls. Paying the base rate correctly but shorting the pension or training fund contribution means the total package is below prevailing wage — even if the paycheck looks right.
A 6-person plumbing crew in California, underpaid after being misclassified for 15 days, could face up to $200/day × 6 workers × 15 days = $18,000 under Labor Code §1775, plus back wages. The Labor Commissioner determines the amount under the statute. This is an underpayment scenario, not a late-filing calculation. Run your scenario through the fine calculator.
Certified payroll checklist for plumbing subs
Before you submit each week, check these — they catch the errors that hit plumbing contractors hardest:
- Every worker classified by work performed — plumber, pipefitter, sprinkler fitter, or apprentice (with period) — matched to the wage determination.
- Split-classification weeks have separate rows with hours allocated to each type of work.
- No "helper" classification used. Workers are either registered apprentices or journeymen.
- Apprentice registration is current and the apprentice-to-journeyman ratio is within limits.
- Fringe components (health, pension, training, annuity) match the wage determination and are documented on the Statement of Compliance.
- Base + fringe meets or exceeds the prevailing wage for each classification.
- State form filed separately if the project has state or local funding.
- Statement of Compliance is signed and dated.
Frequently asked questions
Do plumbing subcontractors have to file certified payroll?
Yes. Every subcontractor on a government-funded public works project must file a federal WH-347 every week the job runs — including weeks with no work (file a "no work" report). Most states with prevailing wage laws require a separate state filing on top. See the step-by-step WH-347 guide.
What's the difference between a plumber and a pipefitter on the WH-347?
Most wage determinations list them as separate classifications at different rates. Plumber covers potable water, waste, vent, and fixtures. Pipefitter covers gas piping, process piping, and high-pressure systems. If a worker does both in the same week, they need two rows with hours split by classification.
How do plumbing apprentice ratios work?
Ratios typically run 1:1 to 1:2 (one apprentice per one or two journeymen), depending on state rules and the apprenticeship standards in the wage determination. Apprentices must be in a registered program. Exceeding the ratio means extra apprentices are paid at journeyman rates retroactively.
Can I use a "helper" classification on prevailing wage work?
No. There is no helper classification for plumbing on prevailing wage projects. If the worker is in a registered apprenticeship program, they're an apprentice. If not, they're a journeyman on the certified payroll, at the full journeyman rate.
Stop fighting the classification math
PrevailComply handles the plumber/pipefitter splits, apprentice ratios, fringe calculations, and state forms that make certified payroll a headache for plumbing contractors. Sign up for PrevailComply, or grab the free WH-347 checklist below.
Related guides
How to fill out WH-347 in 2026 · Free WH-347 generator · Electrical contractor certified payroll · HVAC contractor certified payroll · First-timer's prevailing wage guide · Fine calculator
This guide is general information for plumbing subcontractors, not legal or compliance advice. Classifications, apprentice ratios, wage rates, and remedies vary by jurisdiction and project. Confirm current official guidance and the wage determination attached to your contract. Have qualified counsel review regulatory claims before relying on them for a specific matter.