PHW 006 - Airtightness - Your Building's Windbreaker
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The difference between a building that performs and one that disappoints? One protective layer you can't skip.
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Airtightness - Your Building's Windbreaker
Why Airtightness is the Windbreaker Your Building Needs
Picture this. You're out hiking on a cool day, wrapped in your favourite woolly jumper. At first, you're perfectly comfortable. Then a breeze picks up. The air hasn't changed temperature, but suddenly you're chilled. The wind cuts through, stealing the warm air your jumper was holding.
That's how insulation works in buildings too. It only performs when the air inside it is still. The moment air starts moving through, the insulation's little trapped air pockets collapse, and all its magic vanishes.
Now imagine you add a windbreaker over the jumper. The difference is immediate. The cold air no longer whips through, and suddenly your wool feels warm again.
This is the role airtightness plays in buildings.
The Other Everyday Analogy
Think of standing still in cold water. Your body quickly warms the thin layer around you, and you feel tolerably warm. Start moving? That warm layer vanishes. Fresh cold water rushes in, and the chill cuts deep.
Movement is the enemy of insulation. In water, movement washes away your heat. In buildings, unwanted air movement washes away your insulation's effectiveness.
Two Layers, One Result
It's easy to remember:
Insulation = the woolly jumper (it traps warmth)
Airtightness = the windbreaker (it stops air movement)
Both together = true comfort
You've seen this on every job site. Walk into a framed house on a windy day before the building wrap goes on. Even with insulation between the studs, you feel every gust. That's your insulation failing because air is moving through it.
Now think about the same house after proper air sealing. Suddenly, that insulation works exactly as the manufacturer promised. The R-values become real-world performance.
Insulation without airtightness is wasted potential. Airtightness without insulation doesn't keep you warm. Put them together, and you've got the unbeatable comfort that defines Passivhaus.
"I Don't Want to Live in a Sealed Box!"
This fear comes up all the time, and honestly, it makes perfect sense. Nobody wants to feel trapped. But here's what airtightness actually means – and why your clients will thank you for it.
Airtightness doesn't mean you're trapped in a plastic bag. It means leaks and draughts are gone. The comfort stays in, and the fresh air comes from where you decide. Think of it as upgrading from random gaps to intelligent air management.
Here's the reality that surprises most people:
In a typical Australian home, the air is completely replaced every five minutes by uncontrolled leaks. That's over 10 air changes per hour – like having windows open year-round, whether you want them or not.
In a Passivhaus, the same replacement takes about two hours. That's airtightness working for you, not against you.
But here's the game-changer: Instead of losing warmth and comfort through cracks and gaps, you control exactly when and how air changes. A proper mechanical ventilation system supplies filtered, fresh air all year round while recovering 90% of the heat (or coolth in summer). Your clients get cleaner air than they've ever breathed, with none of the pollen, dust, or traffic pollution that sneaks in through gaps.
The result? No more stuffy rooms, no more cold spots, no more wondering why the heating bill is so high. Just consistently comfortable, healthy air that costs almost nothing to condition.
That's what airtightness delivers, not a sealed box but a perfectly controlled environment.
Proof From Practice
Builders often think airtightness sounds difficult. But those who've done it tell a different story.
Take Stewart Scholten in Australia. His team achieved 0.08 air changes per hour – eight times better than the Passivhaus requirement. His verdict?
"0.6 wasn't hard at all. With a bit of planning, it's easy."
Here's the truth: airtightness isn't about heroic effort on site. It's about smart planning before you start. Get your airtight layer, junction details, and trade sequencing clear upfront. The execution becomes straightforward.
Why Airtightness Matters
It's tempting to think airtightness is just a technical checkbox. But it directly affects comfort, health, and building durability.
Comfort: No more draughts, no cold corners.
Energy efficiency: Heating and cooling demand drop dramatically.
Moisture safety: With air leakage controlled, you stop condensation and mould before they start.
Indoor air quality: Fresh, filtered air without pollen, dust, or pollution sneaking in through gaps.
When insulation and airtightness work together, the building envelope acts like a proper protective shell – warm in winter, cool in summer, and dry all year round.
Bringing it All Together
Passivhaus standards define airtightness clearly: maximum 0.6 air changes per hour under test conditions. That's the level where insulation performs, comfort is guaranteed, and energy use drops to a fraction of typical buildings.
But it's not just about meeting a number. It's about changing how we build. Instead of "patching leaks" once the walls are up, airtightness has to be designed in from the start. Detailing, material choices, and trade coordination all play their role.
And this isn't a burden. It's a chance to build better. To show clients, colleagues, and even skeptics that airtight doesn't mean boxed-in. It means freedom: freedom from draughts, freedom from mould, freedom from high energy bills.
Your Next Step: Make It Practical
Talking airtightness is one thing. Achieving it on site is another. That's why we've prepared a practical Airtightness Checklist you can use on your projects.
It covers:
• Planning airtightness from the very first drawings
• How to detail junctions and service penetrations
• Site practices to keep the airtight layer intact
• Preparing for blower door testing
Attach it to your drawings, walk your trades through it, and you'll turn airtightness from an abstract idea into a routine habit.
Final Thought
Insulation is powerful – but only if it's protected. Airtightness is that protection. Like your windbreaker on a cold day, it's the difference between shivering in layers and feeling truly comfortable.
With airtightness, your building finally performs the way it was designed.
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Next time, we'll explore how Passivhaus is gaining momentum across Australia – and why that creates opportunities for those ready to lead the market.
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[Airtightness Checklist] - Turn airtightness from an abstract idea into a routine habit
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