Feature

Knowing passive design

G Magazine

Maximise the energy efficiency of your house all year round by using the basic principles of passive design.

passive-design

Credit: Farnan Findlay Architects

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Imagine: a home that keeps cool in summer and warm in winter with only minimal reliance on mechanical heating and cooling. Even better, in this house there’s no need to switch on artificial lights during the day. It may sound like an unachievable fantasy, but in fact these are the real benefits of using passive design in your home. It involves maximising a home’s energy efficiency by using design techniques that take advantage of the surrounding climate. From the right orientation to good insulation, passive design is about working with what nature provides to make a home comfortable, wherever you live.

What is passive design?

The principles of passive design are the essential building blocks that every architect and sustainability specialist use when they create a structure. In a nutshell, it means considering the local climate when designing, to maximise a home’s energy efficiency. It involves boosting cooling air movement inside the house and keeping out the sun in summer and, in winter, trapping and storing heat from the sun and keeping the cold out.

“It’s about creating a comfortable environment to live in and trying not to use mechanical means,” says architect Paul Adams, of Modus Architects. “It can make an enormous difference to the comfort of a home.”
There are some universal passive design principles that apply everywhere, and others tailored to local climate. For example, good insulation and effective thermal mass are must-haves in every home. In homes in tropical northern Australia, cross-ventilation is needed to capture cooling breezes, while in cooler southern states the focus is on maximising winter sunshine and sealing the home from drafts.

Using passive design means a more energy-efficient house, which translates to lower carbon emissions and cheaper utility bills. It also makes a nicer space to live in.

“That can’t be underestimated, and people don’t understand that until they’ve lived in a house that works
well,” says Joel Farnan, of Farnan Findlay Architects. “Passive design isn’t so much about architectural design, it’s about thermal comfort and enjoyment of the space.”

Passive design essentials

One of the most important ingredients of passive design is a building’s orientation. The first step in every home design should be considering the local conditions, such as a coastal breeze, along with universal elements, including where the sun rises and sets. These will determine which way a house is oriented, where windows and doors are located, and the layout of interior spaces.

For example, the ideal orientation in Australia is facing north, so that interiors benefit from sunshine and natural light, minimising the need for artificial lights and winter heating.

“I despair when I see these newer developments with the garage positioned facing north,” Farnan says.
Think about the climate and where the sun is needed most during the day in your home. The north side of a house is usually best for the most regularly used living spaces, while the west side will get hot in the afternoon and is better kept for bathrooms and laundries.

Also important, especially in climates with temperature extremes, is insulation. “Insulation is using the building envelope to affect the thermal performance of the building,” Adams says. “Roof insulation is universally important, whether to keep the belting hot summer sun out, or keep heat in during winter.”
Wall insulation, and opting for materials with better insulation performance, such as double brick or double-glazed windows, also helps.

The concept of thermal mass is a key element of passive design, and involves using a heavy mass material, such as concrete or mud brick, to help stabilise the building’s interior temperature.

“It works on the principle that heat will always move towards something cold,” Adams says.

So a tiled floor or internal brick wall exposed to winter sun will absorb heat during the day and will release it slowly as the temperature drops at night.

Heating and cooling tricks

When you consider that 38 per cent of energy consumed in Australian homes is for space heating and cooling, you can understand the importance of passive design to make a home as energy efficient as possible. Also called passive cooling and passive heating, passive design can reduce the amount of mechanical heating or cooling you might need, if any at all.

In terms of heating, insulation, orientation and thermal mass can have the biggest impact. The right orientation will maximise the amount of winter sun you can bring into a house, and good insulation and thermal mass will stop that heat escaping.

“There’s so much energy being given off by the sun each day, particularly in winter, and you can use that to heat your house for free,” Farnan says. “It makes an enormous difference and is much nicer to live with than artificial heating.”

Passive design also extends to maximising a home’s thermal performance by ensuring the home’s ‘envelope’ contains the heat. “In southern climates the biggest things you can do are to work on the thermal performance of a building envelope and seal up gaps and leaks in windows and walls to stop heat escaping,” Adams says.

For cooling, it’s about keeping the heat out and boosting cool air flow in the house. Again, insulation stops heat getting into the house, along with good external shading, particularly over west-facing windows and doors. Strategically placing windows and openings, such as louvres, will create cross-ventilation throughout a house, reducing the need for air-conditioning.

A little or a lot

Clearly, the very best of passive design can be achieved when you’re building from scratch in a carefully chosen location. However there’s a lot you can do with passive design to improve the environmental efficiency of your existing house.

“You can really tailor a house by using eaves to create shade, insulation and materials to suit the comfort expectations of the owners,” Adams says.

Roof insulation and sealing up gaps in windows and doors are effective and relatively inexpensive improvements you can make.

“You can move windows in houses if you find yourself facing the wrong direction,” says Adams. “Just letting
that morning sun in on a winter’s day can make a marvellous change. Zoning is another important thing, strategically placing interior doors so you can zone and manage which areas you heat
and cool.”