BAL Rating – The Bushfire Attack Levels Explained

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Understanding the Bushfire Attack Level (BAL) Rating System

The Bushfire Attack Level, commonly referred to as the BAL rating, is a system used across Australia to assess the level of bushfire risk that a property may face. By evaluating exposure to ember attacks, radiant heat, and potential flame contact, this system provides a structured approach to determine the construction standards necessary for building in fire-prone areas. This assessment follows the Australian Standard AS 3959:2018, a guideline that sets the benchmarks for improving fire resistance in residential structures. Knowing your property’s BAL rating can help inform design choices that maximize fire resilience and protect against the devastating impacts of bushfires.

For those interested in learning more, there are short courses available that offer a detailed understanding of the BAL system, such as

What Do BAL Ratings Mean?

Each BAL rating level specifies different construction requirements, aimed at minimizing bushfire risks in varying environments. The levels, from BAL LOW to BAL Flame Zone (FZ), indicate the intensity of bushfire exposure a property may face. Understanding the specifics of each level helps in making informed decisions about building materials, design, and fire safety features.

BAL LOW: 0 to 12.5 kW/m²

BAL LOW represents minimal risk, where there’s a low probability of direct ember attack or radiant heat exposure. Structures in BAL LOW areas may face fewer restrictions, as radiant heat exposure is unlikely to exceed 12.5 kW/m². While specific fire-resilient construction isn’t mandated, some precautions—like keeping gardens cleared of excess debris and avoiding flammable landscaping—can still be beneficial in reducing risk.

BAL 12.5: Up to 12.5 kW/m²

BAL 12.5 indicates a low-risk area where radiant heat exposure could reach 12.5 kW/m². Although the likelihood of flames reaching the property remains low, there is a higher chance of ember attack, which could ignite flammable materials around the property. To address this, construction requirements suggest using materials like fire-rated timber or metal cladding on exterior surfaces and installing ember-proof screens on vents and openings.

BAL 19: 12.5 to 19 kW/m²

BAL 19 is classified as a moderate risk zone, with radiant heat exposure reaching up to 19 kW/m². Ember attack becomes more likely, and the potential for heat stress on structural materials increases. At this level, specific construction adjustments are recommended, such as the use of non-combustible materials for window frames and doors. Glass should be toughened to resist cracking under heat stress. Bushfire-resistant timber, concrete, and steel are often used to ensure walls and external surfaces can withstand this level of radiant heat exposure.

BAL 29: 19 to 29 kW/m²

BAL 29 is categorized as a high-risk level, with radiant heat exposure reaching up to 29 kW/m². Properties in this category face greater risks of ember attack and radiant heat, requiring more robust construction materials. Building elements like window shutters and ember guards are necessary, and walls may need to be built with non-combustible materials such as brick, concrete, or specially treated timber. Decks and balconies should be constructed from non-combustible or fire-resistant materials to avoid the risk of ignition during ember storms.

BAL 40: 29 to 40 kW/m²

BAL 40 denotes a very high-risk environment, where radiant heat exposure can reach up to 40 kW/m². In these zones, properties must be designed to withstand both ember attacks and direct flame exposure. All building materials need to be non-combustible, including roofing and external walls. Windows should use toughened glass and be fitted with metal shutters for additional protection. Even small gaps around eaves, doors, and windows should be sealed with fire-resistant materials to prevent embers from entering the structure.

BAL FZ (Flame Zone): Over 40 kW/m² and Direct Flame Contact

The BAL Flame Zone, or BAL FZ, represents the highest risk level in bushfire-prone areas, where structures may face direct flame contact and extreme levels of radiant heat exposure exceeding 40 kW/m². At this level, comprehensive fire-resistant construction is essential. Only non-combustible materials are suitable for all external elements. Fire-rated glass is mandatory for windows, and walls should use materials like reinforced concrete or stone. Additionally, extensive landscaping measures, such as establishing clear perimeters and vegetation-free zones, are crucial for reducing fire risks.

Architectural Implications for Bushfire-Exposed Sites

A property’s BAL rating has a significant impact on its architectural design, from the choice of materials to structural layout. Key considerations include:

1. External Walls: For BAL 19 and above, materials must be non-combustible or bushfire-resistant. In BAL FZ zones, reinforced concrete or stone may be necessary for enhanced protection.
2. Roofing: In BAL 40 and BAL FZ zones, roofs must be constructed with non-flammable materials. Additionally, roof junctions must be carefully sealed to prevent ember intrusion, which is particularly important in high BAL zones.
3. Windows and Doors: Windows should be made from toughened glass in BAL 29 zones and above. Installing metal shutters or screens can add a protective layer, reducing the likelihood of glass shattering from heat stress. Doors and frames must also be non-combustible, and all openings should have ember-proof screens.

Closing Structural Gaps

Sealing all structural gaps is crucial in fire-prone areas. Openings around eaves, doors, and windows must be filled with fire-resistant materials, preventing embers from entering the building’s interior. This approach not only minimizes fire risk but also helps regulate airflow, reducing unanticipated ventilation that could intensify fire spread.

Firewater and Rainwater Tanks

Having a reliable water source on hand can be a lifesaver during bushfire season. Fire authorities often recommend installing a dedicated firewater tank for emergency use. Positioned above ground, these non-combustible tanks are equipped with firefighting pumps, providing firefighters with an essential water supply when defending homes from bushfire. Be sure to follow local fire authority guidelines regarding tank placement and maintenance to ensure readiness in emergencies.

Decks and Subfloors

Decks and subfloors should also be built with fire safety in mind. In higher BAL zones, decks should be constructed from non-combustible materials or fire-resistant timber. Additionally, raising deck height and creating defensible spaces around decks can help prevent fires from spreading to the main structure. Some properties may also benefit from installing fire-resistant underfloor shielding.

Maintaining Defensible Space

A key component of bushfire preparedness is maintaining a defensible space around the property. This involves clearing vegetation, reducing the amount of flammable material near the building, and creating a safe perimeter. Defensible spaces help slow down the spread of fire and provide firefighters with a manageable area to defend. For properties in BAL 29 zones and above, consider additional landscaping strategies such as installing gravel paths or firebreaks to further limit fire risk.

In Conclusion

The Bushfire Attack Level (BAL) rating system is an essential tool for assessing and mitigating bushfire risk in residential areas. By understanding the specifics of each BAL level, property owners and builders can make informed decisions about construction materials, design, and safety features. From the structural design to maintaining defensible spaces, BAL guidelines provide a roadmap for creating resilient homes in the face of increasing bushfire threats.

Our team is committed to supporting our community with up-to-date fire safety knowledge and construction expertise. As environmental conditions continue to shift, we remain dedicated to helping property owners build safer, more resilient homes.