BAL rating is the Australian standard for determining the risk of ember attack, radiant heat, and direct flame contact in a home. The BAL rating determines the construction and building requirements needed to protect homes in bushfire-prone areas.
According to the Australian Standard – AS 3959:2018 Construction of buildings in bushfire-prone areas – there are six levels of the BAL rating. In the table below, we’ve broken down each BAL ratings and explained what they mean.
Level of bushfire attack and exposure to radiant heat.
BAL LOW 0 to 12.5 kW per square metre:
The lowest BAL rating can be obtained in a bushfire-prone area, indicating a risk of ember attack but that the potential radiant heat flux exposure will not exceed 12.5kW per square metre. This rating indicates that no special construction requirements exist.
BAL 12.5 0 to 12.5 kW per square metre:
A low-risk classification indicates the possibility of radiant heat flux exposure at a maximum of 19kW per square metre, as well as the risk of wind-ignited embers and burning debris causing an ember attack.
Moderate risk and with potential heat flux and exposure similar to BAL 12.5. Even so, a higher probability of exposure. With no special requirements for the floors and subfloor, the rest of the house has the exact construction requirements except for 5mm safety glass instead of 4mm.
BAL 29 19–29 kW per square metre:
A high-risk rating means the risk of ember attack increases, and the radiant heat flux exposure can reach up to 29kW per square metre. Building requirements are more stringent than for lower ratings.
BAL 40: 29 to 40 kW per square metre:
A very high-risk BAL rating, which means that the risk of ember attack is much higher. With the possibility of direct flame exposure and radiant heat flux exposure of up to 40kW per square metre.
BAL FZ – 40 kW per sq m and flame contact:
An extreme high-risk rating. It is indicating a high risk of ember attack and excessive radiant heat exposure. Furthermore, a likelihood of direct flame exposure will be present. The risk of radiant heat flux exposure is the same as BAL 40.
A building site’s BAL rating dictates the materials and building design elements that must consider. These are some of the design elements and when you should consider them.
Walls on the outside:
External walls with a BAL rating of 19 can use specific materials, namely non-combustible or bushfire-resistant timber. The exterior walls of our Callala project, which is in a BAL-FZ zone (the highest possible rating), are clad in fibre cement cladding for its fire resistance and longevity.
In the case of a BAL 40 rating, roofing materials must be non-combustible, such as steel. Roofs sarked fully, and the junction between the top and the walls sealed entirely where the BAL rating is 12.5 or higher.
Through-the-roof or-through-the-wall penetrations
When you have a higher BAL rating, you must consider any openings that come through walls or roofs, including vents, extractor fans, and downpipes, which should all be made of metal rather than PVC to ensure more heat resistance.
Gaps between cladding, eaves, doors and windows require sealing to prevent embers from becoming lodged in the cracks and catching fire. By preventing uncontrolled ventilation, closing these gaps contributes to a more energy-efficient home.
Firewater and rainwater tanks:
In many bushfire-prone areas, the relevant fire authority in your area may require installing a water tank on-site specifically for firefighters to access this water to defend homes when necessary. Firewater tanks must be above ground, made of non-combustible materials, and equipped with a firefighting pump system.
Decks and subfloors
Floors should be constructed low to the ground with a non-combustible subfloor structure, depending on the BAL rating, non-combustible deck materials or bushfire-resistant timber. Decks are separate structures that and not directly connected to the house; this ensures that if they catch fire, they can detach from the house and burn instead of spreading fire into the home’s main structure.
The Bushfire Attack Level (BAL) rating is an Australian government standard that assesses the likelihood of your homecoming under attack by a bushfire. Bushfire safety is essential, and fire safety knowledge and home building procedures take the highest priority in everything we do.