Smart design for bushfire risk mitigation involves the integration of four elements: landscape design, architectural design, industrial design, and importantly – human behaviour.
The first principle of risk mitigation is to prioritize passive protection over active reactions. For housing in bushfire areas this means prioritising structural resilience above constant vegetation management. Because houses have to perform all manner of functions other than bushfire protection they are, in principle, much more likely to be fire-ready in wildfire emergencies than landscapes which are by nature, dynamic. Simply put, houses can be built and maintained to be non-combustible but their bushfire-prone landscapes, by definition, cannot.
The non-integrated approach is one which is promoted by Fire Authorities and Local and State Governments through Australia. This is where home owners are encouraged to build a somewhat conventional house with poor bushfire resilience, and to achieve their fire protection though constant vegetation management for at least 20 metres around their home – in many cases this is contingent on them clearing and maintaining their neighbour’s properties as well (think of any allotment in a bushfire prone area that is less than 60 metres wide).
The problem here, which has been well documented, is that the vegetation hazard is rarely managed down to the specified Bushfire Attack Level that the approved house was designed for.
We know that most houses burnt down from structural fires ignited by embers, which can travel from many kilometres away. So to build without regard for ember intrusion – regardless of how low the bushfire attack level might – is a flawed logic.
Integrated design is about cross purposing – achieving more with less. So what designers should be looking for here are opportunities to integrate the otherwise disparate aspects of topography, thermal mass, radiant heat protection, insect control, flame contact, thermal comfort, sun shading, site access and escape into one holistic design.
Bushfire prone areas in Australia are also some of the coldest regions of the continent. They experience considerable seasonal variation, being both hot in summer and cold in winter. Often the greatest contributors to the cost of building in bushfire prone areas is not the bushfire standards per se but the energy rating requirements. In these climate zones you need a building with mass – such as masonry – but also an open building with sufficient glazing to capture the winter sun and openings for natural cross ventilation. This presents the cross-purposing opportunity to utilise thermal mass elements as bushfire protection features, and in so doing minimise the construction costs.
Another very practical example of this design approach is to eliminate veranda overhangs and eaves – which are proven weak links in bushfires – and replace these with perforated metal retractable shutters over windows.
These shutters then control the sun, insects, glare and wind as well as embers and radiant heat. Our research has found that this delivers a significant cost saving, but importantly, the bushfire risk mitigation device is used on a daily basis rather than once in an emergency. That is, it is integrated into the daily life of the home – it is not a rarely used add-on.