What is a BAL?
A Bushfire Attack Level, or BAL, rates how exposed a building could be to a bushfire. Here's what it means, in plain English.
What it is, and why it matters
A BAL is a rating of how much a building could be exposed to a bushfire: to burning embers, to radiant heat and, at the highest level, to direct flame. It comes from the Australian Standard AS 3959, Construction of buildings in bushfire-prone areas.
It matters because a BAL determines which construction requirements apply to a new home, or an extension, in a bushfire-prone area. Knowing the likely BAL early helps with where the building goes, its design and its budget.
The six levels
From the lowest exposure to the highest. The number in each name is a measure of radiant heat: the higher it is, the more heat the building could face.
- BAL-LOW
- Very low risk. There's too little vegetation nearby, or it's far enough away.
- BAL-12.5
- Ember attack is the main risk, with some radiant heat.
- BAL-19
- More embers and more radiant heat, and burning debris carried by the wind is more likely.
- BAL-29
- Heavier ember attack and higher radiant heat, enough to damage some building materials.
- BAL-40
- Embers, high radiant heat, and some chance of flames from the fire front reaching the building.
- BAL-FZ (Flame Zone)
- Direct exposure to flames as well as intense heat and embers. Some authorities restrict building here.
What decides a BAL
- The vegetation near the building: what type it is (forest, woodland, scrub, grassland and so on), judged by its structure, because some types burn far more intensely than others.
- How far away it is: the closer the vegetation, the higher the BAL.
- The slope of the ground under the vegetation: fire runs faster uphill, so vegetation on ground falling away from the building is more dangerous.
- The regional fire danger: each part of Australia has a fire danger level, reflecting its climate, that is used in the assessment.
Who needs one, and when
In general, if you're building a new home, or extending or altering one, on land mapped as bushfire prone, your council or building surveyor will need to know the site's BAL before the work is approved. Each state and territory sets its own rules for when a BAL is needed and who can provide it, and some have extra planning requirements, so check with your council or building surveyor early.
Buyers, owners planning upgrades and insurers sometimes want an idea of a site's BAL too.
Method 1 and Method 2
AS 3959 has two ways of working out a BAL. Method 1 is the simplified procedure most sites use: it combines the vegetation type, distance, slope and regional fire danger in a set way. Method 2 is a more detailed calculation, used for steep sites and other cases Method 1 doesn't cover, or where a more site-specific answer is wanted. It's normally done by an accredited bushfire practitioner. BAL Buddy uses Method 1 only.
Questions people ask
Is a BAL the same as a bushfire-prone area?
No. Bushfire-prone area mapping says whether bushfire building rules apply to a piece of land. A BAL rates how exposed a particular building site is, and so how the building has to be built.
Can a site's BAL change?
Yes. It depends on the vegetation around the building, so clearing, regrowth, new planting or a change in how land is managed can change it. Moving the building on the lot changes it too.
Does a higher BAL mean I can't build?
Not usually. A higher BAL means stricter construction requirements, which can add cost. At the highest level some councils restrict or discourage building, so it pays to check early.
Who can do a BAL assessment I can rely on?
It depends on your state or territory. Accredited bushfire practitioners do this work, and in some places councils or building surveyors do too. Ask your council or building surveyor what they accept.
How accurate is BAL Buddy?
BAL Buddy applies Method 1 to what you draw and choose, using public map and elevation data. It's a useful early guide, but vegetation is best judged on site, and only an accredited practitioner's assessment should be relied on for approvals.
Is a BAL the same as the fire danger rating on the news?
No. The daily fire danger rating forecasts how dangerous conditions will be on a given day. A BAL is a fixed rating of a building site, used to decide how the building is constructed.
Does BAL Buddy work everywhere in Australia?
It covers the states and mainland territories. It doesn't cover the external territories, and it can't give a BAL where Method 2 is needed, such as on steep slopes.
This is general information, not advice. BAL Buddy results are not a BAL report.