Understanding the Bushfire Attack Level (BAL) rating system

What BAL ratings mean and how the right materials help protect homes in bushfire-prone areas

Australia has dealt with plenty of bushfires over the years, leaving a real impact on communities right across the country. It’s one of the reasons Australian Standard AS 3959 was created, giving clearer guidance on how to build safer homes in bushfire-prone areas. A big part of that standard is the Bushfire Attack Level (BAL) rating system, which helps homeowners, builders and designers understand what level of bushfire exposure a property might face.

The BAL rating looks at things like ember attack, radiant heat and potential flame contact. In simple terms, it measures heat flux and how much energy a surface could be hit with during a bushfire. Knowing that level of risk makes it easier to choose the right bushfire-resistant building materials and construction methods, so homes in BAL-rated zones are better protected from the start.

There are six Bushfire Attack Level (BAL) ratings set out in AS 3959, each reflecting a different level of potential exposure during a bushfire:

1. BAL-Low: The lowest level of risk, with no special construction requirements, though some areas may still apply basic minimums.
2. BAL-12.5: A low risk rating that recognises the chance of wind-borne embers and burning debris. Some specific construction measures apply.
3. BAL-19: A moderate level of risk with more ember attack and radiant heat up to 19 kW/m². Extra construction requirements are needed here.
4. BAL-29: A high risk rating where homes may face strong ember attack and radiant heat up to 29 kW/m², calling for more robust building measures.
5. BAL-40: A very high risk level with a strong possibility of ember attack, radiant heat up to 40 kW/m² and even some flame contact. Construction precautions are essential.
6. BAL-FZ (Flame Zone): The highest risk category, used in areas exposed to extreme radiant heat and direct flames. Specialised construction and non-combustible materials are a must.

Building in a BAL-affected area means thinking about a few practical design choices that help reduce bushfire risk. The goal is pretty simple: limit where embers can land, keep materials non-combustible and avoid areas where debris can build up. A few key things to keep in mind:

• Opt for non-combustible materials for external walls, roofs, gutters, and downpipes.
• Keep roof designs simple to minimise debris accumulation.
• Minimise open spaces under floors and decks.
• Eliminate gaps between walls and roofs.
• Avoid re-entrant corners to reduce fire risk.

When it comes to materials that make life easier, Fielders® roofing and cladding made from COLORBOND® steel or ZINCALUME® steel is a dependable choice. These products won’t ignite or contribute to the spread of fire, giving you a straightforward way to meet BAL requirements while still achieving a clean, modern look in bushfire-prone areas.