BAL-19 Building Construction Material and Design Requirements

What This Requirement Covers

The BAL-19 requirement describes construction and material standards for buildings located in areas assessed as having a Bushfire Attack Level (BAL) of 19 under AS 3959 Construction of buildings in bushfire-prone areas. It exists to reduce the likelihood of building ignition or structural failure during a bushfire by managing ember attack, radiant heat and, to a lesser extent at this level, direct flame contact. The requirement applies to new buildings, major renovations and certain extensions or alterations in designated bushfire-prone areas where the site assessment calculates BAL-19.

BAL-19 sits mid-range in the BAL scale (which runs BAL-LOW through BAL-FZ). At BAL-19 the main hazard drivers are ember attack and increased radiant heat; construction provisions therefore focus on ember/spot fire exclusion, suitably rated external elements and validated material selections so occupants have greater fire resilience and time for evacuation. This guidance is used by designers, certifiers, builders and homeowners when demonstrating compliance with the National Construction Code (NCC) and associated Australian Standards.

Key Requirements

1. BAL source and standard: compliance based on AS 3959 - Construction of buildings in bushfire-prone areas (relevant edition cited in project documentation) and applied through the NCC (refer to NCC Volume One and any state schedules), and where applicable the ABCB Housing Provisions.
2. External Ignition-Related Requirements (AS 3959 sections applicable):
3. Cladding and external walls: use materials and assemblies with tests or provisions specified in AS 3959 for BAL-19. Non-combustible or limited-combustible cladding is strongly preferred; composite or timber claddings must meet ember protection provisions in AS 3959 (see AS 3959 Section 8 and relevant tables for acceptable materials and required construction details).
4. Eaves, fascias, soffits and sub-floor enclosures: close gaps to resist ember entry. Eaves and soffits should be either non-combustible or constructed and sealed to prevent ember accumulation. Mesh or screening used for ventilation openings must be corrosion-resistant metal with a maximum aperture of 2 mm (or as specified in AS 3959) to resist ember ingress.
5. External doors and windows: glazed elements should use toughened or safety glass meeting NCC glazing provisions where required and be fitted with seals to limit ember intrusion. Timber-framed doors/windows must have ember-tight seals around frames. Where shutters or screens are provided, they must be non-combustible or limited-combustible and fixed to reduce ember penetration.
6. Vents and ventilation openings: all external vents must be screened with corrosion-resistant metal mesh with a maximum aperture of 2 mm (or the aperture specified in AS 3959 for BAL-19). Mechanical ventilation inlets should be located and protected to reduce ember ingress.
7. Decks and balconies: combustible deck surfaces and substructures present higher risk. For BAL-19, protect the sub-floor and underside of decks with non-combustible materials or ember-resistant closures; limit combustible material storage beneath decks. Timber deck boards may be permitted if construction prevents ember accumulation per AS 3959 construction details.
8. Roofs and gutters: roofing materials must be selected per AS 3959. Gutters must be kept clear; gutter guards that are metal and fine-meshed can reduce ember accumulation. Valley and box gutters should be sealed where practical to reduce ember lodgement.
9. Clearing and defendable space: although primarily a site-management matter rather than a building material specification, BAL-19 situations typically require vegetation management to achieve the separation and fuel load assumptions used in the BAL calculation - verify against the site BAL assessment and planning authority requirements.
10. NCC application and referencing: apply BAL provisions where NCC references bushfire measures, and consult the NCC Volume One State schedules where modifications apply (see State and Territory Variations below).
11. Related standards and NCC clauses commonly referenced:
12. AS 3959 Construction of buildings in bushfire-prone areas - clauses and tables for construction requirements by BAL (specific sections on ember protection, material acceptability and construction details).
13. NCC Volume One - relevant clauses and any state schedule modifications (see state schedules in NCC Volume One Schedules 4-12 for jurisdictional variations). Cite NCC Volume One where bushfire provisions are applied through local G-clauses (for example state G-variations such as NSW G5D3 for designated areas).
14. ABCB Housing Provisions where applicable to Class 1 and 10 buildings and referenced standards such as AS 1530 series for fire testing, AS 1562 for cladding installation and other referenced standards in the ABCB schedules.
15. Other Australian Standards that may be relevant depending on assembly type and materials: AS 1530.8.1 (simulated bushfire attack tests for elements of construction - radiant heat and small flaming sources), AS 1530 series for reaction-to-fire testing, AS 4100 and AS 3700 for structural steel and masonry when applicable to wall or substructure choices, and AS 1684 for timber framing detailing where timber is used.

Residential vs Commercial

1. Residential (Class 1 and Class 10):
2. Application of AS 3959 and ABCB Housing Provisions is typical for houses, duplexes and attached Class 10a structures (decks, carports). Construction detail specifications in AS 3959 (e.g., ember mesh aperture, closure of gaps, acceptable cladding types) are implemented directly. The ABCB Housing Provisions may provide material and installation detail references (e.g., AS 1562 for cladding installation). Designers of Class 1 dwellings commonly select non-combustible or ember-resistant external finishes and ensure eaves, vents and sub-floor spaces are sealed as per AS 3959 for BAL-19.
3. Commercial (Class 2-9):
4. For Class 2-9 buildings, NCC Volume One references and additional requirements can apply. There are fewer Deemed-to-Satisfy (DTS) paths for some commercial building types in bushfire-prone areas; projects may need Performance Solutions or specific consultation with the relevant authority. Fire engineering input is more common for large or complex commercial buildings; construction materials and façade systems must demonstrate compliance with AS 3959 requirements or an equivalent Performance Solution accepted by the building regulator. Where a building contains a combination of uses, the more stringent requirements for the applicable part may apply.

Exceptions and Exemptions

1. Where AS 3959 does not provide a Deemed-to-Satisfy solution for a particular building class or situation, a Performance Solution may be developed under the NCC demonstrating an equivalent level of safety. Cite the NCC Volume One clause allowing Performance Solutions and any applicable state G-clauses.
2. Small ancillary structures or minor alterations in some jurisdictions may be exempted or have simplified requirements - check NCC Volume Two or local building regulations and the applicable state schedule for exemptions. For example, very small Class 10 structures or minor works may be excluded from strict AS 3959 construction clauses depending on state provisions.
3. Where planning or development consents impose specific bushfire construction conditions (for example, a condition allowing a different construction solution for BAL-19), comply with the consented solution and document how it meets the required performance standard.

State and Territory Variations

1. NCC Volume One includes state and territory schedules (Schedules 4-12) and some jurisdictions have specific G-clauses or amendments to how bushfire requirements are applied. Examples to check:
2. New South Wales - NSW G5D3/G5P2 and related provisions require AS 3959 compliance in designated bushfire-prone areas, and changes can be made in NSW G clauses to align with the NSW Rural Fire Service guidance and Planning for Bush Fire Protection documents. Refer to NCC Volume One Schedule for NSW variations.
3. Queensland - Schedule 7 (or the Queensland-specific schedule in the NCC) may include modifications; local planning schemes and the state planning policy often apply additional bushfire assessment and conditions.
4. Victoria, South Australia, Western Australia, Tasmania, ACT, Northern Territory - each state/territory adopts the NCC but may have planning controls and state standards that affect how BAL levels are applied and whether AS 3959 is the mandatory compliance path. Always check the relevant state schedule in NCC Volume One and local planning/bushfire authorities for precise statutory modifications.
5. Note: state land-use planning instruments (bushfire overlays, local planning scheme bushfire provisions) also influence requirements and may require higher standards or additional site-based measures beyond AS 3959.

Practical Compliance Tips

1. Obtain a certified BAL assessment from an accredited assessor early in design so BAL-19 (or another BAL) is confirmed and drives material and detailing choices.
2. Use non-combustible external materials where practical - metal roof and gutters, masonry or fibre cement cladding reduce compliance complexity and ember risk.
3. Seal gaps and screen vents with corrosion-resistant metal mesh to the 2 mm maximum aperture (or the aperture specified in the edition of AS 3959 referenced) and ensure seals are maintained over time.
4. Detail eaves, junctions and openings in drawings - inspectors look for closed eaves, sealed junctions and appropriate flashing; ambiguous details often cause noncompliance.
5. Protect gutters and manage leaf build-up - consider metal gutter guards and maintain regular cleaning; ember accumulation in gutters is a common ignition source.
6. Document material compliance - retain product data, test reports and referenced AS 3959 tables or NCC clause citations in the project file to demonstrate compliance to certifiers.
7. Coordinate planning and building approvals - check local planning bushfire overlays, obtain any required planning conditions, and reconcile those conditions with NCC/AS 3959 construction details or an approved Performance Solution.

Citations and references used in this article should be checked against the project-specific edition of the NCC and AS 3959 referenced for the project. Relevant documents include NCC Volume One (and its state schedules), the ABCB Housing Provisions where applicable, and AS 3959 Construction of buildings in bushfire-prone areas, plus supporting test standards such as AS 1530.8.1 for exposed element testing. Always confirm state schedule variations in NCC Volume One and local planning instruments for project-specific requirements.