Due Diligence When Buying a Plumbing Business in Australia
Plumbing businesses in Australia sell for good multiples precisely because they're hard to run well — licensed trades are scarce, margins can be strong, and demand is genuinely non-discretionary. But those same features make them dangerous to buy without knowing what you're looking at. The licences are transferable, or they're not. The work in progress is real, or it's just deposits sitting in someone else's account.
Due diligence for a plumbing business covers the same financial and legal ground as the due diligence process for any small business, but there's a layer of industry-specific risk most buyers skip entirely. This article covers what that looks like in practice.
Why Plumbing Due Diligence Is Different
Most trades businesses involve a licence, but plumbing is unusual because the licence is load-bearing in a way most people don't appreciate until it's too late.
In every Australian state, someone in the business must hold a contractor licence to operate legally — and that licence is not automatically transferred with the business sale. If the seller holds the licence personally and is walking out the door, you need either your own licence, a licensed nominee, or a clear plan for transition before settlement. Miss this and the business stops operating on day one.
The regulatory bodies differ by state: the QBCC in Queensland, the VBA in Victoria, NSW Fair Trading, and equivalent bodies in SA, WA, Tasmania, and the ACT. Each has its own rules around nominee arrangements, supervision requirements, and what happens to existing permits and compliance certificates when ownership changes.
A broker once told me about a deal where the buyer discovered at settlement — at settlement, not during DD — that the outgoing owner held the contractor licence personally and hadn't told anyone. The buyer scrambled to find a licensed plumber willing to act as nominee, which took six weeks and cost a meaningful chunk of the first month's profit. The whole thing was avoidable with a single QBCC licence search.
Licence Verification First, Everything Else Second
Before you spend money on accountants and lawyers, spend thirty minutes on licence searches.
Check the relevant state body's public register. Confirm the licence is current, matches the entity selling (not just the individual), and covers the scope of work the business actually does — plumbing, drainage, and gasfitting are often separate categories, and a business that does all three needs all three covered.
Also check the licence history. Most state registers show complaints, disciplinary actions, and prior suspensions. A pattern of complaints about defective work tells you something. A single unresolved complaint on an otherwise clean record is different from three resolved complaints in the last two years.
Financial Due Diligence — the Plumbing Specifics
Understanding how much a plumbing business is worth starts with understanding what the earnings number actually represents. For plumbing, several adjustments are common enough to deserve specific attention.
Work in progress (WIP). A plumbing business usually has jobs started but not invoiced at any given time. The seller will include WIP as an asset in the working capital calculation — money owed once the job is finished. The question is whether the WIP is real, whether the labour and materials already spent on those jobs have been accounted for, and whether the quoted prices still hold (materials prices in particular can shift on longer jobs).
Ask for a full WIP schedule. Review it against job records and any materials purchased. If the seller can't produce this, treat it as a red flag rather than a minor administrative gap.
Deposit float. Residential plumbing often involves taking a deposit on booking or at parts ordering. Get a schedule of all deposits held, match them against open jobs, and understand who is responsible for completing those jobs post-settlement. If settlement happens and deposits disappear into the seller's account rather than transferring with the business, you've inherited jobs with no revenue to complete them.
Owner's labour. In a small plumbing business, the owner often runs the tools. Adding back the owner's salary is standard normalisation, but if you're not going to run the tools yourself, you need to cost in a licensed plumber at market rates to replace that work. The normalised EBITDA can look very different from the real earnings depending on how this gets handled. Check our guide on key person risk — plumbing businesses are often extreme cases.
BAS and ATO obligations. Get BAS lodgements for the last three years, not just tax returns. Plumbing businesses often have significant GST obligations (they're usually registered), and a history of late or incorrect BAS lodgements tells you something about how the financial administration has been run. Verify there are no outstanding ATO obligations, including PAYG withholding for employees.
Compliance and Certificates
Plumbing and gasfitting work in Australia must be completed to a standard and, in most states, compliance certificates must be issued for certain classes of work. These certificates are records that the work was done correctly and inspected.
During DD, ask for a sample of compliance certificates issued in the last 12 months. You want to confirm:
- The certificates are being issued as required (not skipping them to save time, which is both illegal and a liability you inherit)
- The work described matches what was invoiced
- There are no pending inspection failures or rectification notices from utilities or local councils
Outstanding rectification notices are a specific risk — these are instructions to fix defective work at the business's cost, often on a fixed timeline. A stack of these that hasn't been disclosed is a meaningful liability.
Staff Licences and Trades Composition
The licensed trades within the team are the productive capacity of the business. Do your own verification of each employee's licence — don't rely on the seller's spreadsheet.
For each plumber on staff, confirm their individual licence is current, covers the work they're actually doing, and isn't suspended or conditionally restricted. Check apprentices' enrolment status with the relevant training organisation if the business employs them (apprenticeship rates are a meaningful labour cost, and an unenrolled "apprentice" is legally a labourer paid at the wrong rate).
Also understand the team structure: how many are full-time employees vs sub-contractors? Sub-contractors often look like a cost advantage but carry their own compliance risks — superannuation, sham contracting rules, and workers' compensation can all become your problem if the arrangements aren't properly documented.
Customer Base and Revenue Quality
Plumbing revenue splits into roughly three types, each with different risk profiles:
Emergency callout (burst pipes, blocked drains, gas leaks) — high margin, unpredictable, no customer loyalty built in. Hard to forecast and the work tends to die the moment the seller leaves, since emergency bookings often come from personal referrals.
Scheduled maintenance and service agreements — recurring, lower margin, highly foreseeable. These are the contracts you want, because they survive a change of ownership with proper communication. Ask for a full list of active maintenance agreements, their term, renewal conditions, and cancellation clauses.
New construction and builder work — volume can be good but margins are often squeezed by builders who pay slow. Understand the concentration here: if 40% of revenue comes from one building company, that's a different risk profile than spread across a dozen smaller jobs.
Look at the customer list for concentration and then think about whether you've assessed whether a plumbing business is a good investment in this particular market.
Plant, Equipment, and Vehicles
Plumbing businesses run on vehicles and tools. The condition of both matters for two reasons: replacement cost and what it tells you about how the business has been run.
Ask for a full asset register with age and condition for every vehicle and significant piece of equipment (drain cameras, pipe inspection equipment, pipe relining gear if relevant). Then physically inspect a sample — not just a list. A fleet of vans that are ten years old and never been serviced is a capital expenditure you're inheriting.
Also check vehicle finance. Are the vehicles owned outright, or are there outstanding chattel mortgages or novated leases? Outstanding vehicle finance is a liability that needs to be disclosed in the sale and accounted for in your working capital calculation.
Insurance History
Request the last three years of public liability and professional indemnity insurance claims history. A business with no claims is either well-run or lucky. Multiple PI claims for defective work is a pattern worth understanding before you own the business (and the client relationships that go with it).
Also verify current insurance levels meet your requirements. Some commercial maintenance contracts require minimum public liability coverage — if the existing policy doesn't cover the work, you'll need to adjust on day one.
What to Ask the Seller
Beyond documents, the seller conversations matter. A few questions worth asking directly:
Are there any outstanding complaints or disputes with customers, the regulator, or suppliers? (Ask this on record — if they say no and something surfaces later, it's a misrepresentation.)
What's the transition plan for customers who book because of the owner personally?
Are there any compliance notices, rectification orders, or pending investigations from a state regulator that haven't been disclosed?
Is there any work that was done without the required permits or inspections?
That last question (done without permits) catches more than you'd expect in plumbing. Illegal works create ongoing liability for rectification and can affect the property's insurance and resale value.
A Checklist to Start With
If you want a structured checklist to work through, the Plumbing Business Buyer Checklist covers the full process from initial review through settlement.
This is covered in depth in Module 5 of the Playbook — including how to structure your investigation timeline, what to do when you find something, and how to use DD findings in price renegotiation.
Frequently Asked Questions
What licences do I need to check when buying a plumbing business in Australia?
Check the business's contractor licence with the relevant state regulator (QBCC in QLD, VBA in VIC, NSW Fair Trading in NSW). Also verify individual licences for every employee doing licensed work. Confirm the licence covers all work categories the business performs — plumbing, drainage, and gasfitting are often separate.
Can I buy a plumbing business if I'm not a licensed plumber?
Yes — most states allow a non-licensed person to own a plumbing business provided there is a licensed nominee or nominated supervisor in place. The nominee arrangements vary by state, so get specific advice from the relevant regulator or a trades-specialist lawyer before you sign anything.
How long does due diligence take for a plumbing business?
Allow four to six weeks for a thorough review once you have access to all documents. Licence searches can be done in a day. Financial review typically takes two to three weeks with a good accountant. Legal review runs in parallel. Don't compress this timeline to save time — the risks in a plumbing business are specific enough that rushing past them is expensive.
What are the biggest red flags in a plumbing business sale?
The owner holds the licence personally and has no plan for transition; outstanding rectification notices or regulatory complaints; a WIP schedule that doesn't reconcile with job records; customer concentration in a single builder or property manager; and a vehicle fleet that hasn't been maintained. Any one of these is manageable if disclosed early — the problem is when they surface late.
What happens to existing compliance certificates after a business sale?
Compliance certificates are issued per job, not per business entity, so they remain valid after a sale. What changes is who is responsible for any warranty claims or defect rectification — that's a legal question for your solicitor, and the SPA should address it clearly.
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