Safe As Houses Building safer homes in bushfire-prone areas.
Building or renovating a home in a bushfire-prone area comes with unique challenges – and sometimes significant costs – but the rewards are beyond measure, writes Sarah Pickette.
When Dr Emma Bowen and her family bought a home backing onto Sydney’s Lane Cove National Park, they knew the bushfire risk was high and that it would impact on their future need to extend the small red-brick home as their family grew.
“We love the bush and we accept the fire risk that comes with it,” says Dr Bowen, general manager of the Faculty of Science and Engineering at Macquarie University.
Every new home built in a bushfireprone area must have its Bushfire Attack Level (BAL) assessed to reflect its potential exposure to ember attack, radiant heat and direct flame contact.
Australian Standard 3959 sets out six BAL classifications (BAL LOW, very low risk; BAL 12.5, low risk; BAL 19, moderate risk; BAL 29, high risk; BAL 40, very high risk; BAL FZ [Flame Zone], extreme risk). By complying with the specifications for its BAL classification, a new house will meet the requirements of the National Construction Code (NCC).
The extension to Dr Bowen’s home is rated BAL FZ, and BAL 40 on any walls where BAL FZ-rated bushfire shutters are used. Now the time has come to consider renovation, she and her partner have briefed their architect to design an extension in brick and Colorbond, with two BAL FZ-rated glass doors.
“The doors alone came in at $40,000,” says Dr Bowen. “Plus we’ll install bushfire shutters, use HardieDeck fibre-cement decking and have special gutters and insulation.” After a lengthy wait for development application approval due to issues with trees, the couple received a $500,000 quote from builders to complete the 110m2 extension. For now they are sitting tight, deciding how best to proceed.
Having your BAL assessed is compulsory, but many people don’t realise that following the guidelines of AS3959 isn’t – it’s just one option, says Dr Ian Weir, research architect with the School of Design at Queensland
University of Technology and an expert advisor to the not-for-profit Bushfire Building Council of Australia.
“You can commission your own independent certifier to test for NCC compliance. Whatever they sign off on is what you can actually build,” says Dr Weir. “There’s a lot of misunderstanding about this.”
Anyone considering building or renovating a home in a bushfire-risk area should contact Fire Protection Association Australia (fpaa.com.au) to find a local accredited Bushfire Planning and Design (BPAD) assessor.
“They’ll help you understand the level of risk to your home or prospective home and can write comprehensive bushfire-management plans, which take in everything from vegetation clearance to rainwater-tank and road-access requirements.”
You might expect building in a bushfireprone area to be eye-wateringly expensive, but it needn’t be, says Dr Weir. “Think of something like rammed earth – it’s durable, low-maintenance and will do pretty well in a bushfire,” he says.
Across Australia, bushfire destroyed or severely damaged at least 80 homes in 2017 alone. Those losses come on top of devastating blazes in Victoria, South Australia, NSW, Western Australia and Tasmania in the last decade. Following on from these
events, a raft of new bushfire-rated products have entered the market. Windows and glass, in particular, have benefited from years of research and development in this area. Viridian’s ‘PyroGuard 40’ glass is suitable for BAL 40 zones and using it eliminates the need to install shutters or screens. Stegbar also offers cedar doors and windows that meet BAL 40 certification.
Non-combustible exterior materials are your friend when you have a rating of BAL 29 and above – bricks, fibrecement cladding and aerated concrete products such as Hebel are all good choices. At BAL 12.5 or BAL 19, you can use fire-resistant timber for external wall cladding (ironbark, silvertop ash, blackbutt, for example); you can at
BAL 29, too, as long as the sarking is also bushfire resistant. Above BAL 29, timber usage gets more complicated. You could, however, consider noncombustible HardieDeck (rated BAL FZ) or ModWood’s ‘Flame Shield’, which contains fire retardant and is rated for use up to BAL 40.
Dr Weir says closing gaps in the building envelope and clearing leaf litter from around the home is more important than installing a rooftop sprinkler system. “Ninety per cent of homes lost to bushfire burn down due to embers entering gaps and igniting fires inside.”
Every council will have specific recommendations on clearance zones around the home, says Aaron Neighbour, director of Melbourne firm Atlas Architects. “It’s about having a defendable space; this is one of the most effective ways of reducing the impact of bushfire on your house.”
The construction requirements may be strict (for good reason: human safety) but, at the end of the process, Neighbour says the homeowner is likely to end up with a house in a beautiful, life-enhancing location. “If you work through the building requirements and are prepared to put in the extra dollars (up to $50,000 in some cases), you can achieve a home that satisfies the requirements, looks great and embodies the way of life you seek.”
‘Ninety per cent of homes lost to bushfire burn down due to embers entering gaps in the building envelope and igniting fires inside.’ Dr Ian Weir, architect and advisor, Bushfire Building Council of Australia