A Bushfire Attack Level (BAL) is a measure of a building’s potential exposure to ember attack, radiant heat and direct flame contact that determines the level of bushfire-resistant construction required.
What is a Bushfire Attack Level?
A Bushfire Attack Level, commonly abbreviated as BAL, is used to assess the potential intensity of bushfire exposure at a building site.
The resulting BAL classification determines the level of bushfire-resistant construction required for the building.
BAL assessments are used in conjunction with the applicable building and planning requirements for construction in bushfire-prone areas.
BAL classifications
The BAL system contains six classifications:
- BAL-Low — little or no exposure to direct bushfire attack is expected.
- BAL-12.5 — increasing exposure to ember attack and radiant heat.
- BAL-19 — higher potential exposure to radiant heat and ember attack.
- BAL-29 — higher levels of radiant heat and increased exposure to embers.
- BAL-40 — very high potential exposure to radiant heat, embers and increased likelihood of direct flame contact.
- BAL-FZ — Flame Zone, representing the highest level of bushfire exposure, including direct exposure to flames and extreme radiant heat.
The BAL classification is used to determine the bushfire-resistant construction measures applicable to the building.
How is BAL determined?
A BAL assessment considers the conditions surrounding the proposed building site. Factors used in the assessment include:
- The type and classification of surrounding vegetation.
- The distance between the proposed building and the classified vegetation.
- The effective slope of the land under the vegetation.
- The applicable bushfire assessment methodology and site conditions.
The resulting assessment places the site into one of the BAL classifications.
Why does BAL matter?
The BAL can affect the design and construction requirements of a building in a bushfire-prone area. Higher BAL classifications generally require greater levels of protection for building elements exposed to bushfire attack.
Depending on the circumstances, requirements can affect elements such as external walls, roofs, windows, doors, decks and other parts of the building.
The applicable requirements should be determined from the current National Construction Code, AS 3959 where applicable, and relevant Western Australian planning and building requirements.
BAL and building design
Knowing the applicable BAL can help inform the design, selection of building materials and construction details before plans are finalised.
A BAL classification does not replace the need to comply with the other planning, building and site-specific requirements applicable to the project.
Related terms
Official resource
For current information about building in bushfire-prone areas in Western Australia, refer to the Western Australian Government’s guidance on building in bushfire-prone areas.