Bushfire Attack Level Assessment Process and Site Assessment

What This Requirement Covers

A Bushfire Attack Level (BAL) assessment is the formal process used to determine the severity of a building site’s exposure to ember attack, radiant heat, and direct flame contact from bushfires. The BAL result - expressed as BAL-Low, BAL-12.5, BAL-19, BAL-29, BAL-40 or BAL-FZ - sets performance requirements for materials, construction details and site treatments that reduce ignition risk. The requirement exists to protect life, property and the built environment by applying risk-based construction standards where vegetation and fire behaviour create a potential hazard.

BAL assessment and the associated site assessment procedures apply to new buildings, major alterations and some change-of-use situations located in declared bushfire prone areas, and to developments where local planning or the National Construction Code (NCC) requires demonstration of compliance. Responsible parties include designers, certifiers, building surveyors, homeowners, and builders who must use the BAL to select appropriate construction levels and document compliance.

Key Requirements

1. BAL categories - BAL-Low, BAL-12.5, BAL-19, BAL-29, BAL-40, BAL-FZ as defined in AS 3959. Each category corresponds to increasing ember, convective heat and flame exposure.
2. Assessment standard - Site assessments and BAL determination must be carried out in accordance with AS 3959:2018 Construction of buildings in bushfire-prone areas (latest edition) where referenced by the NCC or planning instruments.
3. Design actions to consider - Evaluations must include ember attack, burning debris and accumulated embers, radiant heat, and direct flame attack, and allow for variations in fire weather, vegetation (fuel loads), distance from vegetation, topography and slope, and duration of exposure (see NCC Volume One and Volume Two assessment clauses).
4. Separation distances - AS 3959 provides procedures to calculate effective separation distances between vegetation and the building which determine radiant heat exposure and flame contact potential. Distances are measured from the building envelope to the edge of the analysed vegetation grouping or fire source, in metres
5. (m) - follow AS 3959 Section 2 and the relevant appendices for step-by-step measurement rules.
6. Radiant heat thresholds - The BAL categories correspond to maximum radiant heat fluxes (kW/m2) used in AS 3959 tables to select construction levels. For example (AS 3959 reference tables):
7. BAL-12.5 corresponds approximately to a radiant heat flux up to 12.5 kW/m2.
8. BAL-19 corresponds approximately to a range around 19 kW/m2.
9. BAL-29 corresponds approximately to a range around 29 kW/m2.
10. BAL-40 corresponds approximately to 40 kW/m2.
11. BAL-FZ indicates direct flame contact and extreme radiant heat beyond tabulated levels.
12. NCC references - The NCC incorporates bushfire assessment requirements in multiple places. Relevant citations include:
13. NCC Volume One - provisions and clauses on bushfire attack levels and design actions (see clauses that reference AS 3959 and state schedules). For example, SA G5D5 and G5D1 note BAL identification where a site is located in a designated bushfire prone area.
14. NCC Volume Two - Class 1 and 10 buildings include an assessment process and requirements (see H7D4 Construction in bushfire prone areas and associated clauses that require application of AS 3959 and assignment of Importance Levels).
15. Importance Levels - For Class 1 and 10 buildings the NCC (Volume Two) requires identification of building Importance Levels (1, 2 or 4) and use of the appropriate annual probability of exceedance (see NCC Volume Two, Section H7 and Table H7V2 for details).
16. Building classes and scope - BAL assessment is relevant to:
17. Class 1 (detached houses and terraces) and Class 10 structures where NCC Volume Two applies; and
18. Class 2-9 buildings where NCC Volume One and associated state schedules apply and where the site is in a declared bushfire-prone area.
19. Documentation - A site assessment must record the vegetation classification, effective slope, distance measurements, chosen assessment method or assumption, and final BAL category. The assessment should cite AS 3959 and the specific NCC clause used (e.g., NCC Volume Two, Section H7D4 for Class 1/10).

Residential vs Commercial

1. Residential (Class 1 and Class 10):
2. The primary reference for most houses and associated non-habitable structures is NCC Volume Two with specific bushfire construction provisions and an assessment process referencing AS 3959. Class 1 buildings must have Importance Levels assigned (commonly Importance Level 2 for typical houses) and use the BAL to select materials, external ember protection measures, and construction details as specified in AS 3959 tables and the NCC Volume Two clauses (see H7D4 and related tables).
3. Lower complexity in regulatory pathway for many small residential projects - BAL assessments for houses are commonly performed by suitably qualified practitioners or via approved simplified procedures in AS 3959 (where applicable), and compliance is demonstrated by specifying construction levels and details in design documentation.
4. Commercial / non-residential (Class 2-9):
5. Commercial, multi-unit and other non-residential buildings normally fall under NCC Volume One. The assessment process is typically more detailed and must account for building classification, higher Importance Levels (e.g., IL3 or IL4 where life-safety or critical infrastructure is involved), site design, egress and building systems.
6. For complex or high-occupancy buildings the site assessment and risk treatment may require engineering inputs, demonstration of active fire protection systems (sprinklers), and cross-reference to specific NCC clauses and state schedules that modify national provisions.

Exceptions and Exemptions

1. BAL-Low: Land assessed or designated as BAL-Low is treated as having no specific construction requirements under AS 3959 - the site is considered to have negligible risk from direct bushfire attack. However, local planning controls or council conditions may still impose requirements.
2. Planning-generated defaults: Some jurisdictions or planning instruments may assign default BALs for specified zones (for example, certain general or medium risk areas may be treated as BAL-Low or BAL-12.5 unless a site assessment is performed) - check local planning instruments and the relevant NCC state schedule.
3. Exemptions for small ancillary structures: Some minor structures may be excluded from full BAL construction requirements depending on the building class, function and state rules - verify against NCC clauses and local council policy.
4. Alternative solutions: Where prescriptive AS 3959 construction is impractical, the NCC allows an engineered alternative solution demonstrating equivalent safety using risk assessment, fire-engineering analysis, or adoption of other standards. Such alternatives must be justified, documented and accepted by the relevant approval authority.

State and Territory Variations

1. The NCC is a national document but each state and territory may adopt schedules, amendments or planning provisions that modify how BALs are assigned and applied. Examples to check include:
2. South Australia - specific insertions (e.g., SA G5D5, SA H7D4) clarify how BALs are applied where the Planning and Design Code identifies risk categories and distances to high risk areas (see NCC Volume One and Volume Two SA schedules for precise wording).
3. Queensland, New South Wales, Victoria, Western Australia, Tasmania, Northern Territory and ACT - each jurisdiction maintains planning maps that declare bushfire-prone land and may have state schedules or local government practice notes that influence default BALs, mapping buffers, and acceptance criteria for site assessments.
4. Always consult the relevant state schedule within NCC 2022 Volume One (Schedules 4-12) and local planning maps or bushfire-prone land registers for jurisdiction-specific rules and mapping conventions.

Practical Compliance Tips

1. Document the measurement process - record how distances to vegetation were measured (horizontal distance to edge of vegetation), the vegetation classification used, and the slope assessment method in accordance with AS 3959. Clear documentation avoids disputes at approval.
2. Start with planning maps - check local council or state bushfire-prone area maps early in design to know whether a formal BAL assessment will be required and to identify likely BAL outcomes.
3. Use qualified assessors for marginal cases - when distances, multiple vegetation groups, or topography are complex, engage someone experienced in AS 3959 site assessments to avoid under- or over-estimating BAL and incurring rework.
4. Include BAL outcomes on drawings - show the assigned BAL on architectural and specification documents and list the AS 3959 construction requirements or alternative solutions so builders know the required materials and details at contract stage.
5. Avoid assumptions about separation - landscape treatments, cleared zones or small garden beds can change effective separation but must be permanent and maintained; temporary or seasonal changes are not reliable for compliance.
6. Be mindful of adjoining properties - the assessment must consider vegetation beyond the subject site; if neighbouring land contributes hazard, document this and include any required mitigation or note on maintenance responsibilities.
7. Check state schedules and planning conditions - some approvals require BAL assessments prepared or endorsed by specific classes of practitioner or may set default BAL assignments; verify and comply with these local requirements.

References: NCC 2022 Volume One - Building Code of Australia (see bushfire clauses and state schedules, and SA G5D5 for South Australia), NCC 2022 Volume Two - Building Code of Australia (see H7D4 Construction in bushfire prone areas and Table H7V2), and AS 3959:2018 Construction of buildings in bushfire-prone areas.