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By Kate Cranney 7 July 2021 7 min read

It’s the middle of winter and you might be feeling the chill of an unwelcome guest: cold draughts blowing through your house.

We’ve written about draughts and how to fix them before. Our scientists are behind one of the only studies on the ‘airtightness’ of Australian homes. The study found that Australian homes are ‘leaky’ by international standards and older buildings are generally much draughtier.

Unintentional draughts are a real issue in southern Australia where they can add up to 20 per cent to your energy bill. Draughts can also lead to grave health impacts. In Australia, the rate of mortality due to thermally inefficient housing and cold weather is 6.5 per cent, almost double that of Sweden (3.9 per cent) — and this almost entirely due to the poor quality of our homes.

Government support and the coronavirus pandemic have fuelled the current construction boom in Australia, which has many searching for more living space. Our old homes may be leaky, costly, and uncomfortable. But new homes don’t have to be. So, what’s happening with new builds in Australia?

Seal it tight or let the breezes flow?

There is currently no specific level of airtightness that new Australian homes need to achieve. The building code states “sealing of the building envelope against air leakage” is required for compliance. But there is no measure as to what an appropriate level of sealing is.

If our ultimate goal is a comfortable, low-energy home, how do we get there? How do we maximise ventilation (air that is allowed to circulate intentionally) and minimise infiltration (air that leaks into and out of homes unintentionally)?

We asked Anthony Wright, former building designer and lead of our Building Simulation, Assessment and Communication team.

“When it comes to a new home, there are basically two different approaches to building design in Australia: a PassivHaus or a free-running approach. They’re sometimes seen as opposites, but they just have a different approach to ventilation and infiltration,” he said.

Let’s look at each in turn.

©  Copyright © Sander van Dijk

PassivHaus design: Sealed tight and insulated right, with high-tech ventilation.

If you use a PassivHaus approach, the building is sealed and highly insulated. That means thermal bridging, which is the movement of heat across a part of the house that conducts heat or cold faster than the materials around it, is not an issue. As a result, the home operates using heat recovery ventilation when needed.

A PassivHaus building is designed and built in accordance with five building-science principles:

Make it airtight

PassivHaus homes are very airtight, featuring very limited gaps and cracks in the house ‘envelope’. Essentially no draughts come in and no air leaks out.

Focus on thermal insulation

PassivHaus homes are very well insulated. Insulation proves thermal comfort and reduces condensation (when you see droplets on cold internal surfaces in winter).

Fresh air through mechanical heat recovery ventilation

Because PassivHaus homes are so airtight, you need to avoid ‘stuffiness’. A mechanical unit is used to bring fresh, filtered air into the home, without losing heat in winter or gaining heat in summer. You might be familiar with this system in larger buildings like offices and hospitals.

High-quality windows and doors

We lose 10-35 per cent of heat gains or losses through single glazed windows and doors. The PassivHaus approach focuses on well-insulated window frames and double- or triple-glazed windows, or low emissivity glass (glass that reflects heat).

Be gone, thermal bridging!

PassivHaus homes aim to eliminate thermal bridging. For example, an aluminium window frame acts as a thermal bridge between the inside and the outside. If you touch an aluminium window frame in winter, it’s likely to be cold. Compared to wood, a metal frame like this will take heat from inside and transfer it outside, leaving your home colder.

Pros and cons of the PassivHaus approach

The PassivHaus approach began in Germany in the late 1980s. With more than 60,000 certified homes globally, it has proven results over 30 years. Because PassivHaus buildings are so airtight and insulated, they retain the warmth or cold generated within. This means they use very little energy to heat or cool, saving you money. PassivHaus homes are also good at removing pollutants in the air via their heat recovery system as you can keep out smog, smoke and pollens from the outside environment. PassivHaus houses are also ‘smart.’ With automated heat recovery ventilation, you don’t need to make decisions about controlling your indoor environment.

There are downsides. PassivHaus homes can be expensive to build. High-quality materials, insulation, high-performance windows and the mechanical ventilation unit all add up. Michael Ambrose — Senior Experimental Scientist and former architect — adds that PassivHaus design may be off-putting for some as it can remove your connection to the outside.

“They are basically sealed boxes that you live in,” he said.

Finally, in an extended blackout, the heat recovery ventilation will not work. As a result, the house may get uncomfortably hot.

So, if you’re the sort of person who likes a home that is a stable and comfortable temperature all year and you don’t want to do more than keep the front door closed to operate it, a PassivHaus may be the approach for you. You’ll find that condensation issues are no longer there, indoor air quality is good, and you’ll be comfortable without thinking about it.

Free-running design: Working with the climate

On the other hand, you can build according to free-running design principles.

Also known as passive solar homes, free-running buildings work with the climate. As Michael explains, some houses in Australia are carefully designed to be ‘leaky’.

“In northern Australia, ‘Queenslander-style’ houses are free-running by design. They’re designed to be open to breezes, to keep the house cooler in summer,” he said.

In a hot climate, a free-running house has several features:

In Australia’s colder climates, a free-running house makes the most of the sun’s warmth through passive solar heating. Such a design avoids the summer sun but maximises the winter sun through orientation (having more windows on northern façades), thermal mass and zoning (a northerly orientation for your daytime living areas).

Pros and cons of the free-running approach

Free-running homes have many advantages. They tend to be cheap to run because they only use ceiling fans and do not have heating or cooling systems like air cons or heaters. Free-running homeowners are more connected to the outside environment and may enjoy knowing how their home works with the outdoors. They may be prepared to put up with a slightly wider range of indoor temperatures and to adjust their behaviour and clothing to suit the weather. They are also usually cheaper to build than a PassivHaus.

Proponents of free-running buildings point out that, in most Australian climates, it’s possible to design buildings that need no heating or cooling. They ask: "why live in a mechanically ventilated esky when you could live in a free-running building, cooled by breezes and heated by the sun?"

But there are some downsides. The biggest issue is with extreme weather conditions. Free-running homes cannot cope with extended heat waves or extremes in cold weather. This may tempt homeowners to install heating or cooling systems into an intentionally ‘leaky’ house, which will be expensive to run. And when air quality is low, for instance during last summer’s bushfires, it may be hard to seal a free-running home to avoid the worst of the smoke haze.

Finally, unlike the automated PassivHaus, you need to know how to operate the home effectively. For instance, knowing when to open and close the windows for the best comfort level. Enthusiasts may be excited by this interaction, but others may want a more automated home.

Curious to learn more? Join our free webinar tomorrow!

You’re invited to a free webinar on PassivHaus v free-running homes this Thursday 8 July. We’ll be joined by representatives from Passive House Association, Earth Building Society, a building scientist and a tropical free running architect.

The panel will answer questions like:

  • What is the best approach for Australia?
  • Which approach delivers buildings that really use less energy?
  • How should regulators accommodate the two approaches?
  • How should we aim to live in an altered climate?

We’ll see you there!

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