BAL-29 Construction Requirements for Windows Walls and Roofs

What This Requirement Covers

The BAL-29 construction requirements define the minimum construction measures for buildings located in areas assessed as BAL-29 under AS 3959 - Construction of buildings in bushfire-prone areas. BAL-29 sits in the middle of the BAL scale and reflects an environment where ember attack, radiant heat, and the possibility of some flame contact are significant. The requirements for windows, external walls and roofs under BAL-29 are intended to reduce the likelihood of façade and roof ignition during a bushfire and to limit the entry of embers and radiant heat into the building.

These measures apply to new buildings, additions and certain major renovations in bushfire-prone areas where the site assessment or planning authority has determined a BAL-29 rating. They are relevant to designers, builders, certifiers and homeowners and must be read alongside AS 3959, the National Construction Code (NCC) / Building Code of Australia provisions (including the ABCB Housing Provisions where applicable) and any state or territory schedule or local authority amendments.

Key Requirements

1. Standard basis: comply with AS 3959-2018 (or the edition referenced by the relevant NCC/state schedule) for construction requirements for buildings in bushfire-prone areas; reference the NCC where AS 3959 is adopted or referenced.

Windows

1. Glazing protection: Where AS 3959 requires protected glazing for BAL-29, windows and glazed doors must use materials and construction that reduce the risk of breakage and ember ingress. Typical measures include: using glazing with appropriate thickness or laminated glass, or installing bushfire shutters or screens compliant with AS 3959 provisions. Exact glazing systems should match the AS 3959 Table requirements for BAL-29 openings.
2. Sealing and screening: Openable windows must be fitted with ember-resistant screens or seals to limit ember entry. Screens should be fixed to prevent gaps and constructed from corrosion-resistant metal mesh where required by AS 3959.
3. Framing and installation: Window assemblies must be installed to avoid direct transfer of structural loads (see ABCB Housing Provisions). Provide minimum 10 mm gap between top of window assembly and loadbearing framing as per ABCB Housing Provisions Standard 2022, Section 8.2.2; packers fixed at sides and bottom as required.

External walls

1. External wall construction: For BAL-29, AS 3959 prescribes acceptable exterior wall materials and construction methods to reduce combustible elements and ember ignition potential. This commonly means non-combustible cladding or fire-resisting systems, or specific tested assemblies listed in AS 3959 for BAL-29.
2. Openings in external walls: Openings (other than protected glazed assemblies) should be minimised and protected in accordance with AS 3959. Where an opening is required, it must meet the protection level in AS 3959 for BAL-29 (for example, non-combustible shutters or screens or glazing assemblies indicated in AS 3959 tables for BAL-29).
3. Fire-resisting requirements where walls are required to be fire-resisting: follow ABCB Housing Provisions Standard 2022, Clause 9.2.3 for FRL requirements when they apply (for example, FRL 60/60/60 when tested from outside, or masonry veneer not less than 90 mm thick where that pathway is used).

Roofs and Roof Coverings

1. Roof covering: Roofs must use materials and installation methods that resist ember attack and ignition. Typical accepted coverings are metal sheet roofing complying with AS 1562.1, roof tiles complying with AS 2049 fixed per AS 2050, or other coverings listed in NCC F3D2 (NCC Volume One) - each of which provides non-combustible or ember-resistant performance when installed correctly.
2. Sarking and underlay: Sarking-type material used for weatherproofing of roofs and walls must comply with AS 4200.1 and AS 4200.2 as referenced in NCC F3D3, and sarking may be required to reduce ember ingress into roof spaces for bushfire-prone buildings under AS 3959 provisions.
3. Roof penetrations and openings: Rooftop vents, valleys and penetrations must be protected against ember entry with ember guards or metal mesh of adequate aperture and corrosion resistance, and flashing sealed appropriately in accordance with AS 3959 guidance and NCC F3D4 for glazed assemblies.

Relevant building classes and regulatory references

1. Building classes: BAL-29 requirements can apply to all building classes where the site is bushfire-prone and AS 3959 applies, but many NCC/ABCB housing provisions specifically address Class 1 and 10 buildings (housing provisions) while NCC Volume One applies across Classes 2 to 9 where relevant.
2. NCC references: Use NCC Volume One and the ABCB Housing Provisions Standard 2022 for installation and fire-resisting wall rules (for example, see NCC Volume One - F3D2, F3D3, F3D4 and ABCB Housing Provisions Standard 2022 Sections 8.2.2 and 9.2.3).
3. Australian Standards: AS 3959-2018 (Construction of buildings in bushfire-prone areas) for BAL construction measures; AS 4200.1/0.2 for sarking; AS 1562.1, AS 2049, and AS 2050 for roof coverings and tiles where referenced; glazing standards such as AS 2047 where glazing resistance to water penetration and installation are required; and other referenced standards for structural and material performance (e.g., AS/NZS 1170.1 for loading where applicable).

Specific numeric measures and thresholds (examples and typical values)

1. 10 mm minimum gap between top of window assembly and any loadbearing framing or masonry wall element for correct installation (ABCB Housing Provisions Standard 2022, Section 8.2.2).
2. FRL for fire-resisting external walls where required: 60/60/60 (ABCB Housing Provisions Standard 2022, Clause 9.2.3(2)(a)).
3. Masonry veneer thickness alternative: 90 mm minimum (ABCB Housing Provisions Standard 2022, Clause 9.2.3(2)(b)).

Residential vs Commercial

1. Residential (Class 1 and 10): The ABCB Housing Provisions Standard 2022 provides specific installation details (for example, window installation guidance in Section 8.2.2) and fire-resisting external wall rules in Section 9.2.3 that commonly govern houses, townhouses and associated outbuildings. Designers often follow AS 3959 in combination with these housing provisions for materials, sealing and ember protection measures targeted at residential construction.
2. Commercial and other classes (Class 2-9): For multi-residential and commercial buildings, NCC Volume One provisions and AS 3959 apply. Higher-rise or non-residential building classes may also trigger additional fire-resistance or separation requirements (for instance differing FRLs, compartmentation or alternative construction solutions) and may rely more heavily on test evidence or engineered solutions acceptable to the relevant authority. The basic BAL-29 material and ember protection intent remains the same but the specific path to compliance can differ and often needs a building-specific assessment.

Exceptions and Exemptions

1. Where AS 3959 or the NCC provides alternative acceptable solutions, these may be adopted if they provide at least an equivalent level of performance. For example, tested assemblies or proprietary systems listed in AS 3959 for BAL-29 may be used instead of prescriptive material choices.
2. Certain buildings or parts of buildings may be exempted from particular glazing requirements under NCC F3D4 (for example, Class 7 or 8 buildings where there is no necessity for compliance with water penetration resistance in that specific case), but exemptions must be verified against the precise NCC clause and state schedules.
3. Renovations or minor works: the extent of upgrade required for existing buildings when BAL-29 is applied can vary - consult the relevant edition of AS 3959 and the local regulator. In some cases, only the altered elements must comply; in others, a higher level of upgrade may be required.

State and Territory Variations

1. Each state and territory may include variations via the NCC state and territory schedules (Schedules 4-12 of NCC Volume One). Common variations include adoption of a particular edition of AS 3959, additional requirements for materials or ember protection, or administrative variations in how BAL ratings are applied. Specific examples:
2. Queensland: Check Schedule 7 of NCC Volume One where Queensland-specific provisions may modify national clauses.
3. Western Australia, Northern Territory and other jurisdictions: may reference additional deemed-to-comply manuals or local standards for high wind or bushfire areas (see ABCB Housing Provisions references to jurisdictional guidance). Always verify the applicable state schedule in NCC Volume One and any local planning or bushfire-prone land overlays.

Practical Compliance Tips

1. - Confirm the correct edition of AS 3959 required by your state/territory and reference it on drawings and specifications. State schedules may require a specific edition.
2. - Use non-combustible or tested assemblies for external cladding and roof coverings; where in doubt specify metal roofing (AS 1562.1) and non-combustible cladding systems listed in AS 3959 for BAL-29.
3. - Ensure all glazed openings are detailed with appropriate seals, screens or shutters and that window installation follows the 10 mm clearance and packing rules in ABCB Housing Provisions Standard 2022, Section 8.2.2.
4. - Protect roof spaces: install sarking compliant with AS 4200.1/4200.2 and fit ember guards to vents and penetrations with corrosion-resistant metal mesh of suitable aperture as recommended in AS 3959.
5. - Document compliance: include AS 3959 references, BAL rating, and specific tested assemblies or product data on the plans and in the specification so certifiers can verify compliance quickly.
6. - Avoid common mistakes: do not leave gaps around window frames, vents or eaves; do not assume standard building practice provides ember resistance; and do not mix combustible eaves linings with unprotected timber framing without suitable ember protection.
7. - Check local council and state planning overlays early: BAL assessments and bushfire mapping can change the required BAL and therefore materially affect selection of windows, walls and roof detailing.

References cited inline above should be read directly for clause and table level detail: AS 3959 (Construction of buildings in bushfire-prone areas), NCC Volume One (see F3D2, F3D3, F3D4), and ABCB Housing Provisions Standard 2022 (see Sections 8.2.2 and 9.2.3). Note that state and territory schedules in NCC Volume One may modify these requirements; always verify against the relevant schedule for your jurisdiction.