How to achieve airtightness in a passive house

Airtightness is one of the five core principles of passive house design, and it plays a major role in helping homes stay comfortable and energy efficient all year round. But achieving airtightness in a passive house isn’t something you can add on at the end. It needs to be included in the planning, design and construction from the start.

Whether you’re in the early stages of designing a passive house or looking to build one soon, this guide explains why airtightness matters, how to achieve it and what to consider when choosing passive builders.

Why airtightness matters

In a conventional home, air leaks can be found around windows, under skirting boards, behind power points and even through the ceiling. That’s a problem, because uncontrolled air movement means heat escapes in winter and hot air seeps in during summer. Your heating and cooling systems have to work much harder, which drives up energy bills.

In contrast, a passive house is designed to dramatically reduce these unwanted air leaks. A properly sealed passive design house uses controlled ventilation, not draughts, to regulate airflow and maintain indoor comfort.

Airtightness helps to:

Reduce heating and cooling demand
Improve comfort by eliminating cold draughts or hot spots
Protect the structure by preventing moisture movement
Support better indoor air quality when combined with a mechanical ventilation system

The role of airtightness in passive house standards

In passive house standards (based on the international Passivhaus standard), a key metric is how much air leaks from the building envelope. To be certified, a passive house must pass a blower door test. This test uses a calibrated fan, fitted into an external doorway, to pressurise and depressurise the home. The amount of air needed to maintain pressure reveals how leaky – or airtight – the house is.

It’s usually carried out towards the end of construction, once the building envelope is sealed, but before finishes like plasterboard or cladding are applied. Some passive builders also do a preliminary test earlier in the build to catch problems sooner.

To pass, the house must achieve no more than 0.6 air changes per hour (ACH) at 50 Pascals of pressure.

That’s much lower than what you’d find in most standard homes, which often have 10–15 ACH. Reaching that level of performance requires careful planning, precise detailing and close collaboration between designers, builders and trades.

Design with airtightness in mind

Designing a passive house means more than just adding insulation and better windows. Airtightness must be part of the overall passive building design strategy from day one.

Your architect or designer should create a simple, compact building form with as few joints, penetrations and complex junctions as possible. Every joint, opening and layer of the building envelope becomes a potential leakage point, so each one must be detailed correctly.

Some important design considerations include:

Choosing construction systems that support continuous airtight layers
Minimising complex roof shapes and wall junctions
Planning services like plumbing and electrical runs to avoid unnecessary penetrations
Selecting materials with known airtightness performance

This is also where passive house designs stand out. By keeping things simple and using proven techniques, designers can create homes that not only perform well but are easier (and often cheaper) to build and test.

Build it right, seal it tight

Even the best design won’t work if the details aren’t followed during construction. Passive builders play a crucial role in achieving airtightness, and it’s important to work with a team that understands the standard and knows how to meet it.

Several areas in a building are particularly prone to air leakage and require special attention:

Junctions between different building elements: For example, where walls meet the roof, or where windows and doors are installed. These are often the weakest points in the airtightness line.

Penetrations through the building fabric: Pipes, cables, ventilation ducts and other services that pass through the walls or roof must be meticulously sealed. Special grommets, tapes and sealants are used for this purpose.

Windows and doors: These need to be high-performance, purpose-built units with robust seals and carefully installed to ensure a continuous airtight connection to the surrounding wall structure. For passive houses in Australia, choosing windows that can cope with both extreme heat and cold is vital.

Floor to wall junctions: Particular care is needed to ensure the airtight layer is continuous from the wall down to the floor slab or foundations.

Airtightness and passive house cooling

One common concern is whether airtight homes get too hot in summer. But a well-designed passive house doesn’t just trap heat – it controls it. By sealing the building and controlling airflow, designers can use passive cooling strategies like:

Cross ventilation (when outdoor conditions allow)
Shading and orientation to reduce solar gain
Heat recovery ventilation (HRV) or energy recovery ventilation (ERV) systems
Thermal mass to absorb and release heat gradually

The result is a home that stays cooler for longer without relying heavily on air conditioning, even during hot Aussie summers.

The bottom line

Airtightness is a cornerstone of passive house standards, and getting it right takes planning, teamwork and attention to detail. But the payoff is worth it – a home that’s more comfortable, more energy efficient and healthier to live in.

If you’re thinking about designing a passive house or upgrading to a passive design house, talk to professionals who specialise in passive building design. From airtightness to insulation and ventilation, every element must work together to deliver the results you’re after.