Innovations for trades in bushfire prone areas

Innovations for trades in bushfire prone areas

After two days it was already the biggest blaze that anyone had ever seen. Birds were falling out of the sky. Almost 90 per cent of residents’ homes were destroyed. It felt apocalyptic. Oh, and there was also a pandemic.

Except we’re not in Mogo or Mallacoota or Hillville. The Great Fire of London devastated the English capital in 1666– and, by incinerating the city’s population of rats and fleas, finished off the Black Plague.

The long-term upshot? Regeneration. Armed with a clean slate, new building codes and innovative thinking, says historian Leo Hollis, “out of the ashes of the Great Fire a modern city was reborn”.

Following Australia’s Black Summer, September’s Australian Bushfire Building Conference (ABBC) sought to spark a similar leap forward. In NSW alone, according to the CSIRO’s Justin Leonard, the fires damaged over 3500 houses – most of which were gutted.

Here are three takeaways from the ABBC.


Don’t dismiss natural building materials.

The demand for natural materials such as straw bales, cob, adobe/mud brick, rammed earth or even hempcrete remains niche. However, these techniques – with their obvious sustainability appeal – can provide impressive structural adequacy, integrity and insulation during bushfires says Viva Living Homes builder Sam Vivers, of the Australian Straw Bale Society.

The ratings for bushfire attack survivability in a home are assessed as a material’s Fire Resistance Level (FRL). The minimum FRL for the ‘Flame Zone’, the highest bushfire attack level, is 30/30/30. This means that three criteria – structural adequacy, integrity and insulation – must each be sustained for 30 minutes under peak fire conditions.

“As a generalisation,” explained Vivers, “30 minutes is what we need to survive a flame front within a building.”

Hempcrete retained strength for 73 minutes across all categories (ie. their figures were 73/73/73). Rammed earth and mud brick and cob walls were very resilient, at 240 minutes (240/240/240), while even straw bales with a layer of 30mm-thick earth render met 30/30/30 requirements.

Bunkers aren’t bonkers – but they’re not a one-size-fits-all solution

Around 85 per cent of building stock in bushfire prone areas doesn’t meet Australian standards and codes designed to perform well during a bushfire event, says Dr Douglas Brown of Bushfire Architecture. This has led to a rise in isolated residents installing on-site (usually) underground bushfire bunkers – prefabricated commercial versions of which (providing just one hour of breathable air) cost around $20,000 to install.

Too often, says Brown, these bunkers are fatally impractical to access in an emergency, and to maintain in other times. Better, he says, to look at “ways we can potentially integrate it within the structure of [the] house”.

That includes linking the main structure to the bunker “via an enclosed walkway which has photo voltaic panels as the roof” and “considering if it might be better to ‘harden’ one part of the main structure of the vulnerable home as a safer ‘refuge’ room”.

Beware express reconstruction

Too many owners demand a fast, like-for-like rebuild without proper consideration of future threat, says expert Blue Mountains bushfire construction architect Nigel Bell.

“People building quickly after a bushfire are the ones least likely to consider [the implications] fully,” says Bell, due to “PTSD, trauma, difficulty”. “They usually want to build exactly what they had, the same project home. They want to resume their life just as it was … it can’t happen.”

Burning embers, says Bell—not radiant heat—destroy 85–90 per cent of buildings. Mitigating that impact must be the dominant design focus, and is much more important than aesthetics.


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