It's one of the most disheartening calls a new homeowner makes: the windows they were proudest of are soaking wet every cold morning, the sills are pooling, and now there's mould in the corners. It feels like the windows are faulty. Usually they're not — and understanding why is the difference between fixing the real problem and paying to replace something that was never broken.
Why your brand-new windows are streaming with water
Condensation forms when warm, moist indoor air touches a surface cold enough to tip that moisture back into water. In a modern home the coldest surface in the room is almost always the window — and more specifically the frame and the junction where the window meets the wall, not the middle of the glass. Air that feels perfectly comfortable in the centre of the room hits that cold line, gives up its moisture, and it runs down onto the sill.
New builds make it worse for two reasons. They're far more airtight than older homes, so the moisture you generate — showers, cooking, drying clothes, breathing — has fewer gaps to escape through. And a new house is still drying out, carrying construction moisture from concrete, render and timber for the first year or more. Airtight, damp, and a cold line at the window: that's the recipe.
Is it normal, or is it a defect?
A little condensation in that first winter can genuinely be the house drying out, and it eases as it does. But condensation heavy enough to pool and run, or persistent enough to grow mould around the reveal, isn't something to wait out. That's the building creating a cold surface, and it's worth diagnosing rather than living with — because the mould is the part that stops being cosmetic.
Mould used to be blamed on the way you live. Increasingly, it's treated as something the building should have been designed not to grow.
Under NCC 2025, condensation and mould management are a compliance matter, judged against a mould index — not a lifestyle afterthought. If mould keeps returning after you clean it, "open a window more" is not the answer; a cold surface is, and it can be found.
Your windows can be fully compliant and still do this
Here's the part that catches people out. Your windows almost certainly carry an AS 2047 certificate and hit their energy numbers (U-value, SHGC) — and that's all true. But an AS 2047 certificate rates the window as a product, tested on its own in a rig; it says nothing about condensation, and nothing about the junction it's installed into. The energy rating rates the window, not the corner it sits in. And the recognised condensation check is run in one dimension, so it never looks at the window-to-wall junction — the exact cold line where your mould is. Three tick-boxes, none of which measured the surface that's failing. Where that leaves the liability is its own story.
So who's responsible?
The chain is clearer than it feels at 7am with a towel in your hand. The window manufacturer is responsible for the window as a product. The builder is responsible for installing and weatherproofing it into the wall, under the NCC. And day-to-day ventilation is the occupant's. When mould is persistent, it's increasingly treated as a design and compliance issue rather than a lifestyle one, so the exposure tends to sit with whoever signed the build off — not the person living there. This is general information, not legal advice; where it lands depends on your contract and the facts. But the single most useful thing you can do is stop guessing and get an independent diagnosis — because that's what moves a builder, a warranty insurer or a tribunal.
How we diagnose it — independently
This is what AFRC Lab does, and the important word is independent: we don't sell windows, and we don't sell the fix. We make our living by being right about the diagnosis, which means the finding follows the science, not a product we're trying to move.
A window audit is a straight, four-step forensic job: we identify and model your actual windows as-installed; we run a TIRS™ thermal simulation to show exactly where the surface goes cold and where the moisture and mould are forming; we hand you a plain-English diagnosis of the real cause; and we give you a vendor-neutral list of what will actually fix it — and can put you in front of trusted people to do whichever solution the science points to.
On one commercial building, the glass was fine — the frame was the whole problem
In a recent forensic audit of a Melbourne municipal office, AFRC Lab modelled the existing windows, ran the TIRS simulation, then validated it on site with thermal imaging. The double-glazed units were performing well; the entire thermal failure was the bare aluminium frame acting as a thermal bridge. The verdict wasn't "replace the windows" — it was treat the frame. The same instinct applies to condensation in a home: the frame and the junction are usually the cold line, and only a diagnosis tells you whether the glass is even involved.
What it costs
- On-site visit and thermal imaging of the problem windows
- Your actual window modelled as-installed
- Plain-English findings: the real cause, not a guess
- A vendor-neutral list of what will fix it
- Everything in the Diagnosis
- A full TIRS™ digital-twin simulation
- A formal, dispute-ready report
- Evidence to put to your builder, insurer or a tribunal
Prices are for sites within 100 km of Moorabbin, Victoria. Travel beyond that is charged accordingly. A diagnosis that stops you replacing the wrong thing typically pays for itself many times over.
What the fix usually turns out to be
Once the cause is clear, the fix is almost never "rip the windows out." Depending on what the science shows, it's usually some combination of improving the reveal and junction detailing, managing ventilation and internal moisture, a secondary or upgraded glazing solution, a frame thermal-bridge retrofit, or — only where it's genuinely warranted — replacement. We'll tell you which, and connect you with people who do it well. (One disclosure, kept in the open: the frame thermal-bridge retrofit system, Thermal Aid, is AFRC Lab's own science, licensed to and sold by a third party — we don't sell it, and it's a commercial-facade product. On homes, our recommendations stay strictly whatever the data points to.)
Stop guessing. Get it diagnosed independently.
Tell us the windows, the rooms and what you're seeing. We'll model what you actually have, show you exactly where and why it's failing, and give you an honest, vendor-neutral path to fixing it — with the evidence to back it if you need it. Melbourne and within 100 km of Moorabbin; further afield by arrangement.
Book a window audit →General information, not legal advice. Where responsibility for condensation or mould ultimately falls depends on the contract, the facts and professional advice. Under NCC 2025, condensation and mould management sit in Parts F8 and H4, with compliance determined from a mould index. AFRC Lab provides independent diagnosis and does not sell windows or remediation products; recommendations are made on the assessed evidence. Thermal Aid is AFRC Lab intellectual property, licensed to a third party who manufactures and sells it. Audit results are indicative to the windows, elements and conditions assessed; final NCC compliance is confirmed by your assessor or certifier. AFRC Lab (Advanced Fenestration Research & Certification) is an independent consultancy; it is not the AFRC. TIRS™ is a trademark of AFRC Lab Pty Ltd.