BAL ratings explained: BAL-LOW to BAL-FZ

A Bushfire Attack Level (BAL) rating is an Australian standard that measures how much radiant heat and ember exposure a building might face during a bushfire. Your BAL rating directly determines the construction requirements for your home and can have a significant impact on building costs. Here is what each level means in plain English.

The six BAL ratings at a glance

BAL Rating	Risk Level	Heat Exposure	Indicative Extra Cost*
BAL-LOW	Minimal	Very low	Nil
BAL-12.5	Low	Up to 12.5 kW/m²	~$5,000
BAL-19	Moderate	Up to 19 kW/m²	~$9,000
BAL-29	High	Up to 29 kW/m²	~$15,000+
BAL-40	Very high	Up to 40 kW/m²	~$25,000+
BAL-FZ	Flame zone	Extreme	Significant

*Approximate additional construction costs for a medium-sized house. Actual costs vary depending on design and materials.

BAL-LOW: Minimal risk

BAL-LOW means the risk of bushfire exposure is very low. There are no specific bushfire construction requirements under AS 3959. This rating applies when the property is sufficiently separated from any classified vegetation, or when the vegetation itself poses minimal risk.

BAL-12.5: Ember attack risk

At BAL-12.5, the building may be exposed to ember attack and a modest level of radiant heat up to 12.5 kilowatts per square metre. Construction requirements at this level focus on reducing vulnerability to embers: sealed gaps, non-combustible roofing, and specific materials within 400mm of the ground.

For properties in medium bushfire risk areas in South Australia, BAL-12.5 is often the deemed rating, meaning a formal assessment may not be required but construction still needs to comply.

BAL-19: Moderate risk

BAL-19 represents an increased risk of ember attack and burning debris, with heat exposure up to 19 kW/m². At this level you are looking at requirements for specific glazing treatments, external wall cladding standards, and subfloor enclosure or protection. The construction cost increase starts to become noticeable.

BAL-29: High risk

At BAL-29, the exposure is significant. Heat flux up to 29 kW/m² and a real possibility of flame contact from burning debris. Construction requirements become more demanding: non-combustible external walls, metal-framed windows with toughened glass, and outdoor decking made from non-combustible materials or bushfire-resisting timber.

This is the level where design decisions made early in the process can save serious money. If vegetation management or setback adjustments can bring you from BAL-29 down to BAL-19, the construction savings can be substantial.

BAL-40: Very high risk

BAL-40 means the building is likely to experience direct flame contact, with heat exposure up to 40 kW/m². This is a high-risk rating that requires extensive non-combustible construction throughout. Properties with a BAL-40 rating may face planning delays and additional scrutiny. In some cases, development may not be approved at this level without significant mitigation measures.

BAL-FZ: Flame zone

BAL-FZ is the most severe rating. It indicates direct exposure to flames and extreme radiant heat. Construction requirements are the most stringent under AS 3959, and specialist construction methods are typically required. Development in a Flame Zone faces the highest level of planning scrutiny, and approval is not guaranteed.

How is the BAL rating calculated?

The BAL rating is determined by assessing three main factors:

• Vegetation type and density: The surrounding vegetation is classified into categories such as forest, woodland, shrubland, scrub, or grassland. Denser, taller vegetation presents a higher risk.
• Distance from vegetation: The setback distance from classified vegetation to the building footprint. Greater distance generally means a lower BAL rating.
• Slope: The effective slope under the vegetation. Downhill slopes can dramatically increase flame length and heat exposure, which is why slope is such a critical factor.

These inputs are processed using the methodology in AS 3959-2018 to produce a BAL rating for each aspect of the building. It is common for different sides of the same property to have different BAL ratings depending on the vegetation and slope conditions in each direction.

Why accuracy matters

An inaccurate BAL assessment can go one of two ways. If the rating is too high, you end up paying for construction requirements you do not actually need. If it is too low, your build may not comply with the standard and could face issues at inspection or, worse, in an actual bushfire.

This is why we believe hands-on firefighting experience matters. Understanding how fire actually behaves in different vegetation and terrain conditions leads to more accurate assessments. We do not just run numbers. We understand the real-world conditions behind them.