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Remember the Black Saturday Bushfires of 2009? In February that year, deadly fires raged across the Australian state of Victoria. It became one of the worst Australian bushfire events on record. The fires were so devastating and deadly that they led to the incorporation of the bushfire attack level (BAL) rating and standards into the National Construction Code (NCC) of Australia.
If you live in an older home in an Australian state prone to or at high risk for bushfires, talk to a contractor about renovating your home. In particular, roof repair and refitting so your roof can meet or even exceed BAL standards can help fortify your home against the potentially catastrophic impact of bushfires.
Understanding the BAL Rating
The BAL rating is a system created to assess the potential exposure of a building to bushfire hazards, namely ember attack, radiant heat, and direct flame contact.
- Ember attack: An ember attack occurs when wind-blown, burning embers from an active fire land on homes or vegetation, potentially starting new fires away from the main blaze. These embers can ignite materials on or near your home, leading to significant damage.
- Heat flux exposure: Heat flux exposure refers to the intensity of radiant heat energy present in an area. It is typically measured in kilowatts per square metre. In the context of bushfires, it describes the radiant heat an area receives from a fire. A high heat flux exposure can cause materials to ignite, weaken structural integrity, and even lead to direct flame contact.
- Direct flame contact: Direct flame contact occurs when flames from a bushfire physically touch a structure or vegetation. Direct fire exposure is one of the most severe bushfire threats, capable of quickly igniting materials and causing rapid destruction.
The BAL rating forms the basis for construction standards designed to improve bushfire resistance. It quantifies a building’s bushfire risk based on factors like the type of vegetation surrounding the property, the distance of the building from that vegetation and the site slope. The Australian Standard (AS) 3959:2018 categorises bushfire attack levels from very low to extremely high:
- BAL LOW: Very low risk; no special construction requirements
- BAL 12.5: Low risk; risk of ember attack and ignition due to radiant heat flux up to 12.5 kW/sqm
- BAL 19: Moderate risk; risk of ember attack and ignition due to a higher heat flux exposure of up to 19 kW/sqm
- BAL 29: High risk; risk of ember attack and ignition due to a heat flux exposure of up to 29 kW/sqm
- BAL 40: Very high risk; considerable risk of ember attack and radiant heat flux of up to 40 kW/sqm; potential for direct contact with flames
- BAL FZ (Flame Zone): Extremely high risk; comes with direct exposure to flames, a heat flux exposure greater than 40 KW/sqm and ember attack
BAL Standards Applicable to Roof Construction
After your home’s bushfire risk or exposure has been determined based on its BAL rating, you may have to renovate your home so it can be more resistant to and resilient against bushfires and related damage. While older homes in bushfire-prone areas are not required to do this, you should still seriously consider doing it anyway.
One of the most impactful changes you can make is to get your roof refitted for fire resistance. The Australian construction standards for roofing are more stringent the higher a home goes up the BAL scale.
- BAL Low: Since there’s a very low risk of ember attack and ignition due to radiant heat, BAL low-rated houses and buildings have no special roofing requirements. You can use ordinary roofing materials and build your roof as usual.
- BAL 12.5, BAL 19 and BAL 29: For homes rated BAL 12.5, BAL 19 and BAL 29 – which correspond to low- to high-risk homes – the Australian construction standards require non-combustible roof cladding, openings and gutters. They also need full sarking and sealed roof junctions.
- BAL 40: BAL 40 or very high-risk homes cannot use roof-mounted air-conditioners. They must also satisfy all the requirements for BAL 12.5, BAL 19 and BAL 29 homes.
- BAL FZ: BAL FZ or flame zone homes must not only satisfy BAL 40 requirements. They must also use materials rated fire-resistant at 30/30/30. This means the material must maintain structural adequacy, integrity, and insulation for 30 minutes. Additionally, roof materials must pass AS 1530.8., the standards that pertain to fire-testing for building materials, components, and structures.
Protect Your Home and Loved Ones From Bushfires
If you live in Victoria, South Australia, New South Wales, and other Australian states prone to bushfires, consider renovating your home to incorporate fire resiliency standards. In particular, your roof is one of the major structural components you should have assessed, repaired, and modified to improve fire resistance.
Getting a BAL assessment and satisfying bushfire-resistance standards are not mandatory for existing homes in bushfire-prone areas. Even so, getting these done is the wise thing to do for your family’s protection and your peace of mind.