What is passive design?

Written by view.com.au in Renovating

Passive design has become a staple of many architectural design awards across Australia, right from Building Designers Association of Australia to one of the country’s longest-running sustainable awards events, Sustainable Building Awards. Beyond the delight that designers get out of building homes with evermore ingenious and beautiful solutions for energy saving and livability, the significant increase of interest in passive design comes down to one thing: climate change.

According to the Building Code of Australia, our country has eight climatic zones, ranging from the Alpine zones down south in NSW, Victoria and Tasmania through to hot and humid summers and warm winters in the north of the country. However, some of the predictability of our climate zones is faltering.

The 2018 State of the Climate report by the Bureau of Meteorology noted that Australia’s climate has increased by 1 degree since 1910, while its surrounding oceans have done the same, meaning wind and weather patterns are harder to predict and now oftentimes much more severe. The southwest of Australia has seen the largest decrease in rainfall than anywhere else in the country, while rainfall has actually increased in some parts of northern Australia.

Passive design aims to work with the environment to stabilise temperatures and energy consumption in a home, essentially doing so without consuming energy or at the very least using as least energy as possible and trying to use sustainable forms of energy.

Passive design is achieved through a range of design techniques and material choices, which is why it has become such a fascinating and innovative area of architecture and home, interior, and landscape design.

Passive design is often separated into three areas, with the most important being the home’s building design, followed by natural and encouraged processes, before finally incorporating a measured (i.e. limited) range of mechanical interventions.

1. ‘Building design’ 

The term ‘building envelope’ comes up a lot in passive design. It refers to the main structure of the buildings (walls, ceiling, roof, windows, floors) and how they are designed to save and even produce energy.

The ‘building design’ is expected to account for the majority of the home’s passive design elements, simply because there are the most opportunities to build passive design into the building envelope.

Some of the core aspects of a building design that can influence energy use and savings are:

  1. The orientation of the building: the climate zone in which your house is will dictate the orientation of your home. Many homes in the southern zones of Australia face north so as to attract as much sun as possible during the day, allowing your building design to turn this into heating and energy. Many homes in tropical areas get too hot and so avoid facing north.
  2. Building materials: the choice of building materials influences your passive design success. For instance, your choice of insulation and the thermal mass of your building will dictate how well the property absorbs, stores and reflects heat energy. If you are working with an architect in building a home or renovating your home, ask them how they are considering thermal mass and building materials in relation to your specific climate. How are they achieving balance through your home’s design?
  3. Floors and windows: glazing plays a huge role in reflecting heat during summer and absorbing much-needed sunshine during winter. Your choice of flooring also impacts how well your home regulates itself, especially when used with mechanical interventions such as solar heating. Finally, an architect needs to consider how to balance the need for an airtight home, where energy cannot be accidentally lost, and the need to incorporate airflow from outside into the temperature regulation of the home.

2. ‘Natural and encouraged processes’

Natural and encouraged processes, when discussed around passive design, relate to how the environment can be utilised to produce and store energy, to avoid consuming energy from the grid or your own reserves, and to improve the liveability of your home.

This is where a large bulk of the ‘design’ work in passive design is done, especially when it comes to innovative uses of interior and structural design.

For instance, clerestory windows are those you often see high up in a home, situated vertically between two separate roofs of the home. These are used to invite more light into a room, much like a skylight, but also allow light and heat to hit an opposing north-facing wall to utilise its thermal mass and improve heat retention in the home during colder months.

Clerestory windows allow light to hit opposite facing walls to collect heat as well as to bring in light to the home.

Clerestory windows allow light to hit opposite facing walls to collect heat as well as to bring in light to the home.

3. ‘Mechanical interventions’

Mechanical interventions include investments in new forms of energy production and storage as well as temperature regulation. These can be electrical heating, solar panelling, wind turbines, roof gardens, grey water systems, water tanks etc. These sit on top of the bulk of your passive design efforts, which involve the actual design of your building and the use of natural processes (wind, rain, sun) to use the least amount of energy as possible. Read more about sustainable interventions here. 

Note: In order to make the most of your passive designs, your need to be actively aware of how to use a home that has been built in this way. When should you open specific windows during the day? How can you measure your energy consumption and storage? Be sure to work with your architect and other designers and draftspeople to understand how passive design has been incorporated into your build so that you can get the most out of it.