BAL rating for an Adelaide Hills home: how it is set

What is a bushfire attack level?

The SA Country Fire Service describes a Bushfire Attack Level (BAL) as a rating used during building design "to assess the intensity of a property’s potential exposure to bushfire. It considers how much radiant heat, ember attack, or even direct flame contact your building might face in the event of a bushfire."

CSIRO’s bushfire guidance, which refers readers to AS 3959:2018, sets out five levels by radiant heat. BAL-12.5 is "significant ember attack, burning debris and radiant heat up to a level of 12.5 kW/m2". BAL-19 and BAL-29 rise to 19 and 29 kW/m2. At BAL-40, "flames from the bushfire front may intermittently contact the house." At BAL-FZ, the flame zone, radiant heat is "in excess of 40 kW/m2" and flames "are likely to engulf part or all of the house."

South Australia’s rules also name BAL-Low, as the level deemed to apply in some areas (below). AS 3959 is a paid Australian Standard; its construction requirements are not reproduced here.

How a BAL rating follows the bushfire hazards overlay

The NCC 2022 glossary defines a designated bushfire prone area as "Land which has been designated under a power of legislation as being subject, or likely to be subject, to bushfires." Ministerial Building Standard MBS 008 states that, for the purposes of the Building Code, a building is in a designated bushfire prone area if it is in an area identified in a bushfire hazard overlay to the Planning and Design Code as "a general, medium or high bushfire risk area", or as "an area within an urban interface area that is within 500m of a high bushfire risk area."

The South Australian variation to NCC 2022 Volume Two, SA H7D4(3), then sets the BAL for a site in a designated bushfire prone area: BAL-Low in general bushfire risk areas; BAL-12.5 in medium bushfire risk areas; "the bushfire attack level assessed for the site in accordance with the requirements of AS 3959" in high bushfire risk areas; and two urban interface bands. Clause 2.3 of MBS 008 states them without overlap: BAL-Low in urban interface areas "within 500 m of a high bushfire risk area and no closer than 100m of the high bushfire risk area", and, "within 100 m of a high bushfire risk area", the BAL "identified by a site assessment carried out in accordance with AS 3959".

The overlay is mapped planning information for an area; the BAL is the level that applies to a particular site and building.

How to find the overlay for an address

The CFS directs owners to the Planning and Design Code’s property lookup: "To check your Bushfire Hazard Rating, go to What is the property address? (Planning and Design Code)". This note does not say which Adelaide Hills localities fall in which category; overlays are read for the specific address, and the council for that address can confirm what applies.

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Who does a BAL assessment in SA?

The CFS planning page states: "When a development application is referred to the CFS under the Planning, Development and Infrastructure Regulations, the CFS Development Assessment Service assesses the development and provides statutory advice." Its FAQ says that if a property is "identified to be in a high bushfire hazard overlay you need to get a BAL assessment undertaken", and names a BAL Application and an Application for preliminary agency advice, the latter with a site plan, elevations, floor plan and materials of construction.

The CFS lists the factors it considers: the vegetation type and arrangement near the home, how close that vegetation is to the building, the slope of the land under the vegetation, and proximity to boundaries and whether the owner can manage the hazard.

Under clause 2.2 of MBS 008, the BAL is determined by the simplified or detailed procedure in AS 3959, or by the deemed levels in clause 2.3. Clause 2.4 adds that where the BAL is determined under AS 3959, "the basis of that determination must be included in the building consent application documentation."

AS 3959 and what the Building Code asks of the house

Performance Requirement H7P5 of NCC 2022 Volume Two applies to a Class 1 building, or a Class 10a building or deck associated with it, in a designated bushfire prone area. It "must, to the degree necessary, be—" designed and constructed to reduce the risk of ignition from embers, radiant heat or flame, "appropriate to the… intensity of the bushfire attack on the building", and provided with vehicular access for fire fighting and a sufficient water supply. Under the national text of H7D4(2), the Deemed-to-Satisfy route is construction in accordance with "AS 3959; or NASH Standard – Steel Framed Construction in Bushfire Areas."

The BAL can reach into other provisions too. Clause 10.8.3 of the NCC 2022 Housing Provisions, on roof-space ventilation, excludes a "roof that is subject to Bushfire Attack Level FZ requirements in accordance with AS 3959", and clause 2.4(b)(ii) of the ABCB Standard for Livable Housing Design sets deck drainage gaps at a step-free entrance "in a designated bushfire prone area" to "that permitted by AS 3959".

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Water supply under MBS 008

MBS 008 describes itself as containing "additional fire safety provisions to those required by the Building Code". Clause 3.1 provides that in a designated bushfire prone area a Class 1, 2 and 3 building "must be provided with or have access to a water supply and fire-fighting equipment" for occupants or the fire brigade. Clause 4.0 states that this "applies to new Class 1, 2 and 3 buildings and to alterations" where the total floor area would increase by at least 50% compared with "the total floor area of the building as it existed 3 years before the date of the application (or, in the case of a building constructed since that time, as it existed at the date of completion of original construction)".

Table 5.2.1 sets the storage and fittings by overlay category, allotment size, BAL and whether the site is connected to mains water. Clause 5.2.6 provides that, except as permitted by 5.2.7, "where the water supply is an above-ground water tank, the tank (including any support structure) must be constructed of non-combustible material, such as concrete or metal". Clause 5.2.7 allows the relevant authority to consider a tank of an alternative material under a performance solution, having regard to listed factors. The CFS notes an underground or enclosed option to be raised with the building certifier.

Knockdown rebuild in a bushfire area, and changing the plans

Clause 4.0 of MBS 008 states that its water supply requirement "applies to new Class 1, 2 and 3 buildings" and to some alterations. The CFS FAQ answers a related question directly — "Do I need another assessment if I change builder, building location on site or layout?" — with: "Yes. Moving the house, changing the size etc, may change your BAL rating or other elements such as the driveway. Your approval is only valid for the plans that were assessed."

The sa.gov.au page adds that a BAL assessment "will help you make decisions about siting your home and how you construct it." Which consents a particular rebuild needs is set by the Act, the Regulations and the Code, and is confirmed with the council for that address; building rules consent may come from a private certifier.

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