Bushfire attack level (BAL): what each rating means for a build

A bushfire attack level, or BAL, is a rating of how much ember attack, radiant heat and flame a house on a particular site could face in a bushfire. It comes from the Australian Standard AS 3959, Construction of buildings in bushfire-prone areas, which sets six levels: BAL-LOW, BAL-12.5, BAL-19, BAL-29, BAL-40 and BAL-FZ (Flame Zone). The rating is worked out for the building site, usually by a bushfire consultant, and it decides how the house has to be built. It only becomes a requirement when the land sits in a mapped bushfire prone area.

The six bushfire attack levels

The numbers in the names are radiant heat, measured in kilowatts per square metre (kW/m²). The higher the number, the more heat the walls, windows and roof have to withstand.

BAL	Radiant heat	What it means for the house
BAL-LOW	Not enough to need a rating	No specific bushfire construction requirements
BAL-12.5	Up to 12.5 kW/m²	Mainly ember attack, with some radiant heat
BAL-19	Up to 19 kW/m²	More ember attack and burning debris, more heat
BAL-29	Up to 29 kW/m²	Higher heat and ember attack
BAL-40	Up to 40 kW/m²	Very high heat, with flames possibly reaching the house
BAL-FZ	Over 40 kW/m²	Direct exposure to flames from the fire front

Each level up adds construction requirements on top of the one below. AS 3959 is not the only way to comply: the National Association of Steel Framed Housing (NASH) standard for steel framed construction in bushfire areas is an accepted alternative in some cases.

How a BAL is worked out

A BAL is not read off a map. It is assessed on the site, from four main inputs:

• The vegetation near the house, sorted into types such as forest, woodland, shrubland, scrub and grassland.
• The distance from the house to that vegetation. This is usually the biggest single factor.
• The slope of the land under the vegetation. Fire runs faster and hotter uphill, so bush on a slope below the house counts for more than bush on flat land.
• The fire weather for the region, set by a fire danger index that varies across the country.

AS 3959 has a simplified method that reads the BAL from tables, and a detailed method that calculates it for sites that do not fit the tables.

Who assesses a BAL

In most cases a bushfire consultant prepares a BAL assessment or certificate, and many hold accreditation under Fire Protection Association Australia's Bushfire Planning and Design (BPAD) scheme. In some situations a council, a building surveyor or the state fire service can assess it. The rules differ by state:

• New South Wales. Development on bush fire prone land has to meet Planning for Bush Fire Protection 2019, the NSW Rural Fire Service document adopted into the planning regulations on 1 March 2020. Complying development (the fast-track approval path) cannot be carried out on land rated BAL-40 or BAL-FZ, and in some cases a BAL certificate from the council or a suitably qualified consultant is needed to confirm the site is not in those two categories.
• Victoria. Every new home in a designated bushfire prone area must be built to at least BAL-12.5. Land in the Bushfire Management Overlay, the planning control for higher risk areas, also needs a planning permit, and a site assessment to AS 3959 sets the BAL.
• South Australia. Under the Planning and Design Code, new buildings in the Hazards (Bushfire - High Risk) Overlay need an on-site BAL assessment. In the Medium Risk overlay, a designated BAL-12.5 applies.
• Queensland. A council designates bushfire prone areas in its planning scheme, and the building rules for bushfire areas then apply to building work inside them.
• Tasmania. A building is in a bushfire-prone area if the land is inside the planning scheme overlay or, where there is no overlay map, within 100 metres of at least one hectare of bushfire-prone vegetation.
• ACT. The ACT Emergency Services Agency maps the bushfire prone area, and the ACT Bushfire Management Standards set the method for assessing BALs there.

What a BAL means for building cost and design

The BAL sets the specification for nearly every part of the outside of the house: ember screens and mesh on openings and vents, the type of glass and window frames, how gaps around the roof and walls are sealed, what the cladding and decking are made of, and how the subfloor is enclosed. At BAL-12.5 the changes are modest and mostly about keeping embers out. By BAL-29 and BAL-40 they reach the choice of windows, doors, cladding and decks. BAL-FZ has the strictest requirements of all and often needs building systems that have passed the standard's fire tests.

A timber deck, a wall of large windows facing the bush or a particular cladding may not be possible at a high BAL, or may need a more expensive tested product.

The main design lever is distance. Because the BAL depends mostly on how far the house is from the vegetation, siting the house further from the bush, or keeping a managed area of low fuel around it, can bring the rating down a level. On a small block hard against a reserve there may be no room to move, and the BAL is effectively fixed.

What to check before you buy

1. Check the mapping first. If the lot is not in a bushfire prone area, a BAL is generally not required. If it is, find out what kind of area: in some states the map category alone sets the minimum (BAL-12.5 in Victoria's bushfire prone areas, or South Australia's Medium Risk overlay).
2. Look at what is next door. Bushland, a reserve or a steep vegetated gully on or near the boundary is what pushes a BAL up. A cleared paddock or a mown park does far less.
3. Get a BAL assessment before you design. It costs far less than redesigning a house once the windows, decks and cladding are chosen.
4. Check the rest of the site too. A bushfire overlay often comes with vegetation controls that limit how much you can clear for that low fuel area. Our guide to property due diligence with planning data covers how the different layers fit together.

For an example of how one region's bushfire classes play out suburb by suburb, see the Adelaide Hills bushfire and flood overlays.

Common questions

What does BAL-29 mean?

BAL-29 means the house could face radiant heat of up to 29 kW/m² in a bushfire, along with significant ember attack. It is the middle of the six levels, and it brings stricter requirements for windows, doors, cladding and decks than BAL-12.5 or BAL-19.

Who does a bushfire attack level assessment?

Usually a bushfire consultant, many of them accredited under Fire Protection Association Australia's BPAD scheme. In some cases a council, building surveyor or the state fire service can assess it. The assessment is done on the site, using the vegetation, distance, slope and regional fire weather.

Can a BAL rating be lowered?

Often, yes. The rating depends mostly on the distance between the house and the vegetation, so siting the house further from the bush, or keeping a managed low fuel area around it, can bring it down. Whether that is possible depends on the size of the block and any vegetation clearing controls.

Is a bushfire prone area the same as a BAL?

No. A bushfire prone area is a mapped area where bushfire construction rules apply. A BAL is the rating for one building site inside that area, and it sets how the house has to be built.

The Property Report shows whether a lot sits in mapped bushfire prone land and the hazard category it falls in, so you know before you book a BAL assessment whether one is likely to be needed. It does not calculate a BAL. Pop in your address or check out a sample report.

LayeredGeo's Property Report pulls together public planning and site data for property due diligence across Queensland, New South Wales, Victoria, South Australia, the ACT and Tasmania, so you can understand a place before you commit.

Sources

• NSW Department of Planning. Planning circular PS 21-010: Development on bush fire prone land. planning.nsw.gov.au
• NSW Rural Fire Service. Building on bush fire prone land. rfs.nsw.gov.au
• Victorian Government. Building in designated bushfire prone areas. planning.vic.gov.au
• PlanSA. State-wide Bushfire Hazards Overlay Code Amendment: frequently asked questions. plan.sa.gov.au
• ACT Emergency Services Agency. ACT Bushfire Management Standards, version 1.2. esa.act.gov.au

About this article. Published by LayeredGeo and written from the published research cited in the Sources section above. It is general information about how property and ground conditions are assessed in Australia, not engineering, planning, legal or financial advice, and it is not specific to any property. Check anything that matters against the source dataset or a suitably qualified professional before you rely on it. If you spot something wrong, tell us at hello@layeredgeo.com.au and we will fix it.

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