- Replacing a roof “like for like” doesn’t dodge the rules. New roofing work has to meet the current National Construction Code and Australian Standards. The tribunal threw the like-for-like argument straight out.
- We won the building dispute on the report, not the noise. Every defect was pinned to a specific NCC clause or Australian Standard, with the cause of the water ingress spelled out in plain English.
- A patio builder did the roofing. He wasn’t a registered roof plumber, and the workmanship reflected it.
- SAT ordered him to pay $18,975 to put the roof right, plus $2,277 in costs — just over $21,000 all up.
- The inspector who wrote the report gave the evidence. Same person, same findings, start to finish — that consistency is what tribunals back.
“At SAT, a roof replacement dispute is won or lost on the expert evidence. This one was a textbook example of why.”
— Russell McCarthy, Registered Builder & Lead Building Inspector
This is a recent roof replacement dispute in Perth that landed at the State Administrative Tribunal, and it’s worth walking through because it shows exactly how these matters are won. A homeowner paid for a new roof, it leaked, the contractor refused to wear it, and the whole thing turned on one independent expert witness report. Here’s what happened and why the evidence carried the day.
The Roof Replacement That Ended Up at SAT
A homeowner down in Hamel — I’ll call her Karen — had an old corrugated iron roof. Patched, getting on in years, but watertight. Inside stayed dry even in a downpour. She knew it’d need doing eventually, so she went looking for someone to replace it.
A contractor quoted her $15,000 to strip the old tin off and put on new Colorbond — new sheets, new screws, new flashings, new insulation, the lot. She paid a deposit, the work got done over about ten days in late 2023, and on the day it looked fine. She paid the balance and moved on.
Then the first proper winter rain came through in July 2024. Water came in at the back of the house, right where the roof meets the verandah. Ceiling damaged. A puddle on the floor. She messaged the contractor.
His answer? The gutters must’ve backed up. Or the rain came in sideways. And the line that ended up front and centre at the tribunal: all I did was replace what was there.
That’s where it became a formal building dispute. She served a notice of complaint, and from that point the contractor went quiet — wouldn’t engage with her, wouldn’t engage with the Building Commissioner, just stopped responding.
Where Our Building Inspection Came In
Karen got us out in September 2024. As a registered builder and building inspector, I went over the roof against the standards — the same way I’d approach any defect liability inspection where a builder’s work is in question.
And it wasn’t one or two things. The roof was non-compliant in a long list of ways, and a few of them were the direct cause of water getting into her home.
The two that mattered most:
The sheets were barely overlapped. Where corrugated sheets join, you need a proper overlap — 150mm to 200mm depending on the pitch. The overlaps here were about 50mm. Water tracks straight through a join like that.
The back section was pitched too low. Corrugated profile needs a minimum 5-degree pitch — and getting roof pitch wrong is one of the most common causes of a leak we see. The rear of this roof was flatter than the minimum, which is why it let water in every time it rained hard. That section needed either a trapezoidal profile or the pitch lifted to spec.
On top of that the overhang had no proper anti-capillary break — no fold, not enough length — so wind-driven water blew up under the bottom of the sheets. Add in dodgy flashings, unsealed fixings, and gutters and downpipes that didn’t meet AS 3500.3, and you’ve got a roof that was never going to hold up. This was textbook non-compliant roofing.
Here’s what I keep coming back to: this is what happens when someone who mainly builds patios takes on a roof. It’s not the same trade. The whole reason we push people towards using a registered builder for the work is so it gets done — and checked — properly the first time.
“He told her he’d done roofing ‘occasionally’. The roof told a different story. Replacing a roof isn’t like-for-like joinery — it’s regulated work, and it has to comply.”
— Russell McCarthy
Why the Expert Witness Report Won the Dispute
A report that just lists complaints doesn’t win at SAT. The tribunal member isn’t a builder. My job is to translate the construction issues into something they can clearly assess — and tie every defect to the rule it breaches.
That’s what this report did, and it’s the same structure that feeds straight into a Scott Schedule. The tribunal leaned heavily on it — it lined up with two other independent reports on file — and rejected the contractor’s like-for-like argument outright. Here’s a slice of how the key defects stacked up:
| Defect found on the roof | What the standard requires | Why it mattered |
|---|---|---|
| Sheet overlaps only ~50mm | NCC 2022 — 150mm–200mm end lap depending on pitch | Water tracked straight through the joins |
| Rear roof pitched under 5° | NCC 2022 — 5° minimum for corrugated profile | Corrugated sheet can’t shed water at that pitch |
| No anti-capillary overhang/fold | NCC 2022 — 10mm overhang with fold | Wind-driven rain blew up under the sheets |
| Flashing joins not sealed | Manufacturer guidelines + AS 3500 | Open paths for water entry |
| Gutters/downpipes undersized & unsupported | NCC + AS 3500.3 | Drainage couldn’t cope, ponding everywhere |
In the published decision (Foster and Jarvis [2026] WASAT 68), the tribunal found the work was not carried out in a proper and proficient manner, and that those defects were the source of the water ingress. Because Karen had already had the roof properly re-done by the time it reached hearing, the tribunal ordered the contractor to pay the cost of putting it right — $18,975, after a small deduction for one item outside the original scope. And because he’d refused to engage the whole way through and didn’t even turn up to the hearing, it awarded a further $2,277 in costs to cover my report and my time giving evidence.
This is the part most people miss: this is exactly what a properly built SAT expert witness report is meant to do. Itemise each defect, reference the standard, explain the cause, set out the fix. Nothing flashy — just clear and defensible.
“Showing up matters. He didn’t lodge a thing, didn’t turn up, and the unreasonable conduct cost him on top of the rectification bill.”
— Russell McCarthy
The Real Lesson — Use the Right Trade and Get It Checked
A few things to take from this one.
If a contractor replaces your roof and it leaks, “I only put back what was there” doesn’t get them off the hook. Once you do the work, you own the standard.
Use the right trade. A patio builder is not a roof plumber. The same logic is why we bang on about getting a proper Practical Completion Inspection and construction stage inspections on a new build, a thorough pre-purchase building and pest inspection on an established home, and an advanced building and pest inspection with thermal imaging where moisture is a risk — get the right eyes on it before the money changes hands, not after the ceiling’s wet. If water’s already getting in, a dedicated waterproofing inspection will tell you where and why.
And if you’re already in a fight with a builder, the report is everything. A clear, standards-referenced expert witness report — backed by the same person turning up to explain it — is what tribunals rely on. That’s the whole job.
Frequently Asked Questions
Can a builder avoid responsibility by saying they replaced the roof “like for like”?
No. The tribunal rejected exactly that argument here. If you remove and replace a roof, the new work has to comply with the current National Construction Code and Australian Standards. “It’s the same as the old one” isn’t a defence.
Do I have to use a registered roof plumber for a roof replacement?
You want the right registered trade for the job. In this case the contractor mainly did patios and only occasionally touched roofing, and the workmanship showed it. The cost of getting it wrong dwarfed any saving.
What actually made the expert report win this roof replacement dispute?
Every defect was tied to a specific standard, the cause of the water ingress was clearly explained, and the rectification scope and cost were set out plainly — structured so the tribunal could assess each issue on its own, the same way a Scott Schedule works.
How much does a SAT expert witness cost in Perth?
It depends how far it goes. As a guide: the initial defect liability report is $499 + GST, an expert witness report is $499 + GST, a conferral/expert response package is $1,250 + GST, expert time is $350 per hour, and tribunal attendance is $2,200 + GST (half day) or $4,200 + GST (full day). Most clients start with the defect report inside the warranty period, which often settles things before SAT is even needed.
What happens if the builder doesn’t show up to the hearing?
The hearing can proceed without them, which is what happened here. And refusing to engage can backfire — the contractor’s conduct was a factor in the costs order made against him.
Do I need a lawyer for a SAT building dispute?
Usually not. SAT is built for people to represent themselves, and most building disputes are decided on the technical evidence, not legal argument. A credible expert witness is generally more effective, less stressful and far cheaper than going down the legal route.
Related Reading
- Our building dispute expert witness service in Perth
- Building and pest inspections across the Peel region
- Mandurah building inspections
- How often should you have your roof inspected?
- Water ingress inspections: what goes unseen
- Areas we service across Perth and WA
If you’re staring down a dispute with a builder and you’re not sure where you stand, get in touch with our team or book your inspection online. The earlier we get a report in front of you, the stronger your position.