Running a Commercial Plumbing Business in Australia
The site foreman asks you to move a stack 300mm to the right to accommodate a change in the mechanical drawing. You do it. It takes your crew half a day. You note it mentally. You submit your progress claim at month end without the variation. The head contractor pays your claim. The variation never gets paid. That half day costs you $600. Do that three times a month and you're undercharging by 15–25% on a project that's already priced tight. Commercial plumbing is high value, high potential — and won by the operators who capture every dollar of their work.
What commercial plumbing looks like
What kills commercial plumbing margins
Variations — the silent margin killer
In commercial plumbing, design changes are the norm, not the exception. Architectural drawings change. Mechanical and electrical services clash with your hydraulic rough-ins. The builder decides to move a wet area. Each of these changes affects your scope, your labour, your materials, or all three.
The operator who captures every variation in writing, gets it signed before proceeding, and includes it in the monthly progress claim is consistently the most profitable operator on any given project. The operator who does the work first and worries about getting paid later consistently undercharges by 15–25%.
The non-negotiable variation process:
1. Scope change is identified on site → 2. Variation created digitally on your phone (description, estimated cost, date) → 3. Sent to project manager for written approval → 4. Work proceeds only after written approval → 5. Variation included in next progress claim with reference to approval number.
A site foreman's verbal "yeah mate, just do it" has no legal standing in a variation dispute. Project managers and head contractors know this. They're counting on you not knowing it too.
Retention — money you're owed but can't touch
On most commercial projects, the head contractor withholds 5–10% of each progress claim as retention security. On a $100,000 subcontract at 5%, that's $5,000 of your money sitting in the head contractor's account for 12–18 months after practical completion. Across multiple concurrent projects, retention balances can represent a material amount of cash that you're effectively lending at zero interest.
Most commercial plumbers track retention poorly — or not at all. They finish a project and only remember the retention 6 months later when someone on the accounts team notices the final invoice was never raised. By then, the head contractor may have gone into administration, disputes have arisen, or the trail has gone cold.
Track every retention holdback from the first progress claim. Set a calendar reminder for both retention release milestones — practical completion and defects liability period end. Invoice for the retention at each milestone without waiting to be asked.
Daily labour diaries — your best defence
On commercial projects, your daily labour diary is the most important document you produce. It records who was on site, what they did, what materials were used, and any access or delay issues. If the head contractor disputes your progress claim or refuses to pay a variation, your daily diary is the primary evidence of what actually happened.
A site supervisor who records this information in a job management app at the end of each day — rather than trusting their memory until month end — gives you a factual, timestamped record that is essentially impossible to dispute.
Where commercial plumbing money gets lost
| Stage | What You Need | What's Actually Happening |
|---|---|---|
| Quoting | Hydraulic drawings reviewed for design clash risks. Provisional sum for design changes built into contract. Clear variation trigger clause. PO number process confirmed before mobilising. | Tender price squeezed to win. No variation clause. PO process unclear. Scope based on drawings that have already been superseded. |
| Job Management | Daily labour diary recorded by supervisor on site. Every variation created digitally and approved in writing before proceeding. Photos of work completed at each milestone. | Variations actioned on verbal foreman approval. Daily diary updated weekly from memory. Photos taken but not attached to job records. |
| Invoicing | Monthly progress claims submitted on contract schedule. All approved variations included with reference numbers. Retention tracked from day one. Milestone reminders set for retention release. | Monthly claims submitted but variations omitted. Retention not tracked. Retention invoice never raised. Month-end catch-up invoicing instead of real-time tracking. |
| Payments | 45-day terms built into cashflow forecast. Escalation process for overdue payments documented. Security of payment legislation used when needed. Materials deposit required for large-spec material orders. | 45-day terms treated as unexpected. No escalation process. Security of payment legislation never used or even known about. Materials procured before payment received on previous claim. |
What commercial plumbers actually need from software
For commercial plumbing at scale, simPRO (Brisbane-built, used by major AU contractors) or AroFlo handle variation management, progress claims, retention tracking, and daily labour diaries in one platform. For smaller commercial operations, ServiceM8 or Tradify cover the variation and documentation requirements adequately.
Compare job management tools →Xero handles progress billing, retention tracking, and job cost reporting better than most other AU accounting platforms. The integration with simPRO and AroFlo means progress claims flow from job management to accounting without re-keying. Retention balances visible at all times.
Compare accounting tools →Commercial plumbing requires significant plant — pipe threading machines, pressure testing equipment, vans, trailers. Equipment finance preserves cashflow for working capital while allowing the business to operate with the right tools. Chattel mortgage is the most tax-effective structure for equipment in most circumstances.
Compare equipment finance →Doing commercial plumbing work and wondering where the margin went?
The Strategy Builder identifies whether it's variation capture, payment terms, or retention management — and the highest-leverage fix for your commercial plumbing operation.
Build My Free Strategy →Frequently Asked Questions
Written variation approval before work starts — every time, no exceptions. When a scope change is requested on site: stop work, create a digital variation with description and estimated cost, send it to the project manager (not just the site foreman), and proceed only after written approval. A site foreman's verbal "just do it" has no legal standing. It takes 2 minutes to create a variation record. It takes months to recover an unsubstantiated claim.
Retention is a percentage (typically 5–10%) withheld from each progress claim as security against defects. Released at practical completion and defects liability period end (typically 12 months later). Track every retention holdback from the first claim in your job management system. Set reminders for both release milestones. Invoice for retention at each milestone without waiting to be asked — head contractors rarely volunteer to release it proactively.
Submit progress claims on the schedule agreed in the contract — typically monthly. Reference contract item numbers, percentage complete for each line item, and all approved variations with reference numbers. The more specific and evidenced the claim, the less room for dispute or QS reduction. Vague or unsupported claims are the ones that get cut. Your daily labour diary is the evidence that supports every line in the claim.