How Does a Bushfire Attack Your Home?
When people think of bushfire damage, they often imagine flames engulfing a house directly. But the reality is more complex. In fact, many homes lost to bushfire are located over 700 metres from the fire front—and most are not destroyed by direct flame contact.
To understand how to protect your home, it’s essential to know the three ways bushfire can cause damage.
Three Modes of Bushfire Attack
A home may be exposed to one or more of the following during a bushfire event:
Embers and burning debris
Radiant heat
Direct flame contact
Among these, ember attack is by far the most common cause of house loss.
Ember Attack: The Silent Threat
After the Ash Wednesday bushfires in 1983, the CSIRO analysed more than 1,150 damaged or destroyed homes. The study (Ramsay & Rudolph, 2003) found that ember attack—not direct flames—was the leading cause of home destruction.
Embers are burning leaves, twigs or debris carried by the wind, often hundreds of metres ahead of the main fire. These embers can lodge in roof cavities, accumulate in gutters, or ignite flammable materials near buildings. If unchecked, they can ignite the structure itself.
Defending against ember attack is crucial. Buildings that lack ember protection are especially vulnerable—even when far from the fire front.
Radiant Heat: A Secondary Factor
Bushfires emit radiant heat in the form of infrared energy, which pre-heats fuels and accelerates the fire’s spread. While this heat is intense, the CSIRO found it generally peaks for only 60 to 90 seconds as the fire front passes—not long enough to destroy most buildings built to standard (Ramsay & Rudolph, 2003).
Still, radiant heat should be accounted for in construction to reduce risk and improve survivability.
Direct Flame Contact: The Most Severe
This occurs when flames from the fire physically reach and touch a structure. In the investigation into the 2011 Roleystone and Kelmscott fires, WA’s Fire and Emergency Services reported that buildings damaged by direct flame contact often lacked adequate asset protection zones (APZs).
A properly maintained APZ (formerly known as BPZ) provides a defensible space between the structure and vegetation. Standard construction methods alone are unlikely to withstand direct flame contact, making landscape management critical.
How BAL Assessment Helps
Your Bushfire Attack Level (BAL) assessment identifies the most likely form of bushfire attack your planned build/property may face. Based on this, it prescribes construction requirements under AS 3959, the Australian Standard for building in bushfire-prone areas.
Complying with your BAL rating can make the difference between surviving a fire—or losing your home to it.
Want to understand what your BAL means for your build?
Check these posts out for a plain-English breakdowns of BAL levels and the construction changes involved or costs involved: