What This Requirement Covers
The BAL-40 construction requirements and ember protection provisions apply to buildings located in areas assessed as Bushfire Attack Level 40 (BAL-40) under AS 3959-2018 Construction of buildings in bushfire-prone areas. BAL-40 represents a high potential for exposure to ember attack, burning debris impact and radiant heat up to 40 kW/m2, so the construction requirements are intended to reduce the risk of ignition and structural damage during a bushfire. These measures protect fabric, limit points of ember entry, and provide enhanced resistance of external elements likely to be exposed to flame contact or high radiant heat.
This requirement primarily applies to new and substantially renovated buildings in bushfire-prone areas where the site assessment has determined BAL-40, including many residential dwellings (Class 1 and Class 10a structures), but PCC (Performance) or deemed-to-satisfy provisions may also affect Class 2-9 buildings depending on jurisdictional schedules in the National Construction Code (NCC). Compliance is achieved by following AS 3959-2018 in combination with the NCC (NCC Volume One / Volume Two or applicable state schedules) and any relevant local planning conditions.
Key Requirements
- Radiant heat exposure: BAL-40 corresponds to a design radiant heat flux of 40 kW/m2; construction measures must resist ember attack and burning debris impact and provide protection against that heat level as specified in AS 3959-2018.
- External wall materials and protection: External walls and associated junctions must use materials, fixings and construction details listed in AS 3959 for BAL-40 (see AS 3959-2018, Section 7 and Appendix C tables). Where openings occur, they must be protected as specified for BAL-40. Where the NCC requires an FRL, external systems may need to meet relevant FRL values when tested per NCC references.
- Doors and windows: All glazed openings and glazed doors must meet the ember and flame protection requirements and, where listed in AS 3959 for BAL-40, be fitted with bushfire-compliant screens or shutters and glazed with appropriate glazing- and framing-assemblies. Acceptable protection options for doors and windows are those specified in AS 3959-2018 for BAL-40 (see Section 8 and tables for protected openings).
- Vents and eaves: External vents, sub-floor vents and eaves must be protected against ember entry using mesh or other approved barriers with an opening not greater than 2 mm in any dimension unless a different size is specified in AS 3959 for that element. Eave and sub-floor closures must follow AS 3959 BAL-40 details.
- Roofs and roof coverings: Roof coverings, ridges and junctions must meet the material classifications and installation details in AS 3959 for BAL-40. Flashings, valleys and roof penetration details must be sealed to prevent ember entry and constructed from materials compliant with AS 3959 BAL-40 requirements.
- Decks, pergolas and appendages: Decks or timber elements attached to the building must comply with the BAL-40 construction details in AS 3959. Use ember-resistant materials and protect the junctions to the building fabric in accordance with AS 3959 tables for BAL-40.
- External combustible elements: Minimise use of external combustible cladding, trim and joinery. Where combustible elements are used in proximity to the building envelope, follow AS 3959 BAL-40 separation, shielding or protective construction details.
- Bushfire ember protection: Ember screens, seals and closures at junctions, vents, windows, doors, under eaves and around services must comply with AS 3959 for BAL-40. Mesh openings typically must be no greater than 2 mm and made from corrosion-resistant material as specified in AS 3959-2018.
- Services and utilities: LPG cylinders, gas meters, woodpiles, combustible storage, and other hazards must be separated from the building or protected by construction methods consistent with AS 3959 and NCC Spec 43 where applicable; separation distances such as 10 m (see NCC Spec 43 S43C4/S43C5) can apply for certain building types or when using alternative protection.
- Relevant building classes: Primarily addressed to Class 1 and Class 10a buildings under the housing provisions when using NCC Volume Two and AS 3959; Class 2-9 buildings may be captured by NCC Volume One and state schedules where AS 3959 is mandated (see NCC Volume One clauses G5D2/G5D3 and Spec 43 references).
- NCC and Standards references: The primary standard is AS 3959-2018 Construction of buildings in bushfire-prone areas (Sections 3, 7, 8 and relevant tables for construction requirements by BAL). NCC references include NCC Volume Two (housing provisions) where AS 3959 is cited, NCC Volume One clauses and Specification 43 where applicable (see S43C2, S43C4-S43C6), and the ABCB Housing Provisions. Other referenced Australian Standards may be relevant for materials and components, e.g., AS 1530.8.1 for radiant heat testing, AS 1684 for timber framing practices when applicable, AS 3700 for masonry, and AS 4100 for steel structures when structural elements are steel.
Residential vs Commercial
- Residential (Class 1 and Class 10a): The BAL-40 provisions in AS 3959-2018 are directly referenced by the NCC Volume Two housing provisions. Deemed-to-satisfy construction details for external walls, roofs, openings, vents, eaves and attachments for BAL-40 are provided in AS 3959 and incorporated into housing practice. Builders and designers should follow the AS 3959 tables and construction details specifically prepared for BAL-40.
- Commercial and other classes (Class 2-9): The NCC Volume One governs these classes. For buildings in bushfire-prone areas, NCC Volume One requires compliance with AS 3959 in many cases (see G5D2/G5D3 or state schedules). However, for some building types and BAL levels above BAL-12.5 there are no Deemed-to-Satisfy provisions and a Performance Solution (G5P2) may be required. Specification 43 in Volume One sets out requirements for some non-residential buildings (S43C2, S43C4 - S43C6) and may impose additional separation distances (for example 10 m) or FRL requirements (for example external walls FRL 60/60/60 when tested from outside in specific scenarios) instead of or in addition to AS 3959 details.
Exceptions and Exemptions
- Performance Solutions: For Class 2-9 buildings or where Deemed-to-Satisfy provisions do not apply (for example BAL exceeding BAL-12.5 in certain building types), a Performance Solution under NCC G5P2 may be required. This can allow alternative methods to achieve equivalent safety where strict AS 3959 details are impractical.
- State schedule modifications: Some states have specific schedules or modifications that alter how AS 3959 must be applied. Where the state schedule prescribes a different approach, the state schedule in NCC Volume One or Volume Two takes precedence for those buildings.
- Minor structures: Very small, detached, non-habitable Class 10b structures or certain minor works may be exempted from full BAL-40 construction where local planning or NCC provisions provide an exemption; check NCC Volume Two and local planning provisions.
- Alternative materials and testing: Where an alternative material or system demonstrates compliance by testing (for example meeting AS 1530.8.1 criteria for a given radiant heat flux) or by a certified Performance Solution, it may be accepted in place of a prescribed AS 3959 detail.
State and Territory Variations
- NSW: NSW inserts or modifies clauses in NCC Volume One, for example NSW G5D3/G5P2 require AS 3959 compliance for many building types in bushfire-prone areas and may require consultation/conditions via the NSW Rural Fire Service for higher BALs. Check NSW-specific G5 provisions in NCC Volume One and Planning for Bush Fire Protection guidance.
- Victoria: Victoria uses NCC Volume One with State variations such as G5D4 and Specification 43 references for certain Class 9 buildings; local planning overlays also apply.
- Queensland, South Australia, Western Australia, TAS, ACT, NT: Each jurisdiction may include schedules (Schedules 4-12 in NCC Volume One) or local planning instruments modifying how AS 3959 and BAL construction are applied. For example, NCC Volume One Spec 43 contains provisions that reference separation distances, FRL alternatives and non-combustible paths (see S43C4-S43C6). Always verify the relevant state schedule in NCC 2022 Volume One (Schedules 4-12) for local amendments.
- Note: State schedules can change frequently; always confirm the current state schedule in the NCC and any local planning authority bushfire planning overlays or conditions.
Practical Compliance Tips
- Ensure an AS 3959-2018 site assessment is completed early in design to determine the correct BAL and avoid late design rework. BAL-40 changes many external-detail requirements.
- Use 2 mm corrosion-resistant mesh for vents and openings where AS 3959 requires it for BAL-40 and ensure all gaps and junctions are properly sealed to prevent ember entry.
- Detail junctions between roofs, walls, eaves, decks and services with ember seals and non-combustible flashing to the AS 3959 BAL-40 tables; builders often miss small gaps at service penetrations and cable entries.
- Select non-combustible or low-combustibility external finishes where practical, and document compliance with AS 3959 tables and any material test certificates (for example AS 1530.8.1 where required).
- For Class 2-9 buildings or complex sites, engage a fire engineer or certifier early if a Performance Solution under NCC G5P2 may be required; do not assume housing provisions will directly apply.
- Check state schedules and local planning conditions for additional separation requirements (for example 10 m setbacks) or FRL requirements (for example external walls to 60/60/60 in certain Spec 43 situations) and incorporate them into siting and design.
- Keep clear documentation on site: the BAL assessment, AS 3959 construction details used, material specifications and any test reports or performance evidence to present to certifiers or council.