In addition to regular construction standards, residential buildings* in designated bushfire areas are required to comply with “Australian Standard AS3959 – Construction of buildings in bushfire-prone areas”.
The aim is for the building to “provide a measure of protection to the building occupants (until the fire front passes) as well as to the building itself”. The standard is used to determine:
The potential threat level to the building from bushfire-prone vegetation; and
The construction standards that apply for the determined threat level.
Potential BAL Threat Ratings
The six threat levels (known as Bushfire Attack Levels, or BALs) are based on the potential radiant heat exposure to a building, and AS3959 details the construction standards relevant to each BAL.
BAL-LOW
There is insufficient risk to warrant specific construction requirements.
BAL-12.5
Ember attack.
BAL-19
Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux.
BAL-29
Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux.
BAL-40
Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux with the increased likelihood of exposure to flames.
BAL-FZ
Direct exposure to flames from fire front in addition to heat flux and ember attack.
The Western Australian Building Commission provides resources and information, including answers to a comprehensive range of Frequently Asked Questions, relating to building standards in bushfire areas.
While designed to improve safety, it should be noted the “measure of protection” provided by AS3959 is no guarantee that a building will withstand a bushfire. It is also crucial to have ongoing management of the bushfire threat and a clear emergency action plan.
* residential buildings include class 1,2 and 3 buildings, and any associated class 10.
Jeremy Durston (BPAD36525)