MOST NEW HOMES ARE BUILT TO CREATE MOULD (UNLESS YOU ASK YOUR BUILDER THESE 5 QUESTIONS)
Mitch Chan - 06.02.2026
Most people think mould comes from leaks, humidity, or not cleaning well enough. But the truth is far more unsettling: the way most homes in Australia are built practically guarantees mould will grow inside the walls - even when the home is brand new.
I’ve seen it in million-dollar builds, architect-designed homes, and renovations that looked flawless from the street… but were quietly spreading illness behind the plaster. And the families living in them had no idea.
What makes mould so dangerous is that the symptoms show up long before the mould ever does - especially in people who are genetically sensitive to it. For those people, a home that looks perfectly fine can still make them seriously unwell.
It often starts with symptoms that feel random or unrelated:
fatigue that never lifts, no matter how much you rest
allergies that flare indoors but disappear outside
headaches, dizziness, or brain fog that come and go
constant viral infections that never fully clear
And for children, the impact can be even more distressing: sleep issues, behavioural changes, recurring infections, learning difficulties - signs parents often blame on school stress, diet, or “growing pains,” never imagining it could be the house itself.
It doesn’t discriminate, either.
Jordan Peterson, one of the most recognisable public figures in the world, spent years battling unexplained illness before doctors finally traced the cause back to mould exposure.
It happened to him. It happens to thousands of people. And it can happen in any home.
In most cases, it comes down to four building decisions most homeowners never see, and most builders were never taught.
But the consequences are always the same…
1. The Wrong Wall Wrap (Sarking) Is Still Being Used Almost Everywhere
Most Australian homes still use a shiny, non-vapour-permeable foil wrap - the same product that’s been used for decades. It traps moisture inside the walls instead of letting it escape, creating the perfect environment for mould. Builders use it because it’s familiar, it meets minimum code, and it’s what they were taught. But “meeting code” and “building a healthy home” are two very different things.
2. Builders Aren’t Taught How Mould Actually Forms
TAFE still teaches outdated building methods, and the NCC hasn’t caught up to what we now know about moisture, air movement, and building science. Most builders don’t understand how mould grows, how easily it spreads, or how building assemblies should be designed to prevent it. It’s the blind leading the blind, and homeowners pay the price.
3. Frames Are Often Lined While They’re Still Wet
Rain during construction is normal. What’s not normal is lining walls while the frame is still holding moisture. If timber is enclosed while wet, that moisture has nowhere to go - and mould will grow, guaranteed. Proper builders test the frame to around 14% moisture content before lining, or use dehumidifiers to bring it down. Most don’t. They’re pushed by timelines, weather delays, or habit. And once those walls are closed, the problem is sealed in.
4. Homes Are Built Airtight… But Not Breathable
Healthy homes are both airtight and breathable. Most homes in Australia are airtight and sealed - a dangerous combination. When warm indoor air meets cold surfaces inside sealed wall cavities, condensation forms. That water sits in the insulation, the timber, and the plaster. Over time, it feeds mould from the inside out. It’s not visible or obvious, but it affects the home every single day.
The Difference Between a Healthy Home and
A Sick Home Is Just a Few Small Choices
There’s a misconception that building a mould-resistant home requires a much bigger budget, but the numbers tell a very different story. In most cases, the cost difference between a home that traps moisture and a home that manages it properly is tiny. Often less than 1% of the total build cost. That’s the part almost no homeowner realises, because the steps that prevent mould aren’t flashy upgrades.
They’re smarter choices made at the right moment.
And that’s the real lesson here: creating a healthy, mould-resistant home doesn’t cost more… it just requires a builder who understands how to do it.
What This Means for Your Renovation or New Build
Once you understand how mould really forms, the whole idea of choosing a builder looks different. Price, timelines, and finishes still matter, but they’re not the things that decide whether your home will stay healthy in the long run. What matters most is whether your builder understands moisture, airflow, and the way a modern home should be assembled.
And the good news is, you don’t need to be a building expert to figure that out. You just need to ask the right questions, and know which answers should concern you.
Questions to Ask Any Builder Before You Sign:
1. “What type of wrap do you use, and why?”
You want to hear: a vapour-permeable system that lets moisture escape.
Red flag: “We use the standard foil sarking everyone uses.” (That’s the wrap that traps moisture inside the walls.)
2. “How do you make sure the frame is dry before lining?”
You want to hear: moisture testing or we wait until the frame is under 14%.
Red flag: “If it looks dry, we go ahead.” (Visual dryness means nothing.)
3. “What happens if the frame gets wet during construction?”
You want to hear: we wrap early or we use dehumidifiers if needed.
Red flag: “It’ll dry eventually.” (It won’t - not once it’s sealed.)
4. “How do you manage condensation inside the wall system?”
You want to hear: breathable layers, correct sequencing, ventilated cavities.
Red flag: “Condensation isn’t really an issue in our climate.” (It absolutely is.)
5. “Can you explain how your wall system breathes?”
You want to hear: airtight on the inside, breathable on the outside.
Red flag: Anything vague, defensive, or unclear. (If they can’t explain it simply, they don’t understand it.)
At the end of the day, a healthy home isn’t a result of luck or budget.
It’s the outcome of a builder who knows how to control moisture.
When you know what questions to ask, you stop comparing quotes and start comparing competence. And that’s what protects your family, your investment, and your home for decades.
If You Want a Healthy Home at the End…
You Need the Right Decisions at the Start
When you step back and look at the whole picture, the real issue isn’t mould at all. It’s that most homes are still being built on assumptions that no longer match how modern houses actually behave. We’re building tighter, more insulated, more energy-efficient homes, but we’re not building them with the moisture management those homes require. And that’s why even brand-new, high-end builds can end up with the same mould problems as older, neglected ones.
The advantage you have now is awareness. You know how mould really forms, what causes it, and the kinds of decisions that protect your family long before the walls go up. Most homeowners never get that clarity - they move through the process blind, trusting that “meeting code” means “built for health.” As you’ve seen, those two things are not the same.
If you’re planning a renovation or new build, the best place to start is with clarity, and that’s exactly why we created our free guide:
Your Home Reimagined: A Guide to Exceptional Home Renovations
Inside, you’ll learn:
the early decisions that quietly shape your home’s long-term health and performance
how to approach your project in the right order, so every choice supports your budget
what separates a home that simply looks finished from one that’s designed to last
It’s a simple read, but it can save you months of stress and thousands in rework.
And if you’d like to talk through your plans or understand how these principles apply to your own home, we’re always here to help. Whether you’re still exploring options or ready to take the next step, we can walk you through what really matters before you commit to a single drawing.
You’ll walk away with more clarity, more confidence, and a renovation or new build designed to support your family’s comfort, health, and wellbeing for years to come.
