Roofing Material Requirements for Bushfire Attack Levels

What This Requirement Covers

These requirements govern the selection, construction and installation of roofing materials where a site is in a bushfire‑prone area, expressed as a Bushfire Attack Level (BAL) under AS 3959. They exist to reduce the risk of ignition and flame penetration to buildings from ember attack, radiant heat and direct flame contact during a bushfire. The rules cover roof coverings, roof penetrations, sarking/underlayment, eaves and junctions, and combustible material in roof spaces where such elements could allow flame ingress or ember accumulation.

The obligation applies to new buildings and to certain alterations and additions on sites designated as bushfire prone. Applicability is determined by the assessed BAL for the site (BAL‑LOW, BAL‑LO, BAL‑12.5, BAL‑19, BAL‑29, BAL‑40, BAL‑FZ) in accordance with AS 3959 and the NCC state schedules. The National Construction Code (NCC) and referenced standards (notably AS 3959 Construction of buildings in bushfire prone areas) set the Deemed‑to‑Satisfy pathways; higher or alternative measures may be used as a Performance Solution.

Key Requirements

1. Roof materials and construction must satisfy the bushfire construction provisions in AS 3959 (current edition) for the site BAL, as adopted by the NCC (see NCC Volume One G5D3/G5D5 or state equivalents). Specific roofing requirements in AS 3959 include details for roof covering material, sarking, exposed edges and gaps to prevent ember entry.
2. For BAL‑FZ (flame contact) sites:
3. Roof coverings, flashings and roof penetrations must be non‑combustible or be constructed to prevent flame contact as specified in AS 3959 Section 9 (Construction for BAL‑FZ). External combustible joinery and attachments are generally not permitted where they would be directly exposed to flame contact.
4. Roof perimeter and junctions must be sealed to prevent ember entry; sarking is typically required behind roof coverings.
5. For BAL‑40 and BAL‑29:
6. Use of non‑combustible or ember‑resistant roof coverings is required as per AS 3959; sarking or an equivalent ember‑blocking layer is required behind roof coverings at ridges, hips and penetrations.
7. For BAL‑19 and BAL‑12.5:
8. Roof coverings should be installed in accordance with manufacturer instructions and AS 3959 guidance for ember protection; sarking or ember stops are recommended/required at junctions where AS 3959 specifies them.
9. For BAL‑LOW and BAL‑LOW (or BAL‑LOW equivalent):
10. Standard roofing materials permitted by the NCC may be used, but where the local planning overlay or state schedule applies a higher BAL then the higher BAL rules override.
11. Sarking/underlay requirements:
12. Where required by AS 3959 for the applicable BAL, a sarking or ember‑blocking underlay must be installed behind roof coverings and sealed at penetrations and eaves. The NCC also sets roof space ventilation rules (see NCC Volume One, Clause F8D5) which interact with ember protection: roof space ventilation must still meet minimum free open areas (e.g., 25,000 mm2/m at each end for pitches <10°; 7,000 mm2/m at eaves and 5,000 mm2/m at high level for 15°-75° roofs) while preventing ember ingress.
13. Roof penetrations and junctions:
14. Penetrations (skylights, vents, flues, plumbing stacks) must be sealed or fitted with ember guards or non‑combustible collars as required by AS 3959 for the site BAL. Flashings and cappings must be installed to prevent ember accumulation and entry.
15. Combustible roofing components:
16. Timber battens under combustible roof coverings and combustible ridge cappings are restricted at higher BALs; install non‑combustible ridge and hip cappings or sarked solutions where AS 3959 requires them.
17. Building classes and application:
18. The bushfire roofing provisions in AS 3959 and the NCC apply across building classes where the site is bushfire prone. For Class 1 and 10a (residential and outbuildings) compliance is typically via NCC Volume Two and AS 3959 references. For Class 2-9 buildings, the NCC Volume One provisions and G5D3 (or jurisdictional equivalents) apply and may require a Performance Solution for some BALs (see NCC Volume One, G5P2).

References: NCC Volume One - Building Code of Australia (G5D3, G5D5), NCC Volume One Clause F8D5 (roof space ventilation), AS 3959 Construction of buildings in bushfire prone areas (sections on roof coverings, Section 9 for BAL‑FZ). Where waterproofing or membrane roofs are used, see NCC Volume Two H2D8 and AS 4654 for membrane systems.

Residential vs Commercial

1. Residential (Class 1 and 10) buildings:
2. Typically regulated under NCC Volume Two where AS 3959 is the primary reference for BAL construction (Volume Two cross‑references and jurisdictional adoption apply). Deemed‑to‑Satisfy provisions may be available for low to moderate BALs via AS 3959 guidance; sarking, ember stops and non‑combustible flashings are commonly specified for BAL‑29 and above.
3. Roof space ventilation requirements in NCC Volume Two/H2D8 and F8D5 remain relevant when adding sarking or ember stops because ventilation openings must not provide ember ingress paths.
4. Commercial and other class buildings (Class 2-9):
5. Regulated under NCC Volume One. For Class 2-9 buildings, some BALs (notably BAL‑12.5 in certain situations) may require a Performance Solution rather than a Deemed‑to‑Satisfy solution under G5P2. The NCC may require consultation with fire authorities or modification by state schedules for these building classes.
6. Larger or higher‑risk commercial buildings may require fire engineering assessment to demonstrate that roofing and roof space systems meet Performance Requirements for life safety and structural integrity under bushfire exposure.

Exceptions and Exemptions

1. BAL‑LOW: Sites assessed as BAL‑LOW generally do not require the AS 3959 construction measures for roof materials beyond normal NCC material requirements, unless local planning overlays or state schedules demand higher measures.
2. Exemptions by state or condition: Some states include specific exemptions or modified BAL assignments in their NCC schedules (see State and Territory Variations below). Where a state schedule prescribes a different BAL mapping (for example, automatic BAL‑LOW for certain urban interface zones), the state provision governs.
3. Performance Solutions: Where a Deemed‑to‑Satisfy roof solution is impractical, an accredited Performance Solution (fire engineering report) can be submitted under NCC provisions (e.g., NCC Volume One, Performance Requirements) to justify alternative materials or construction, provided it demonstrates an equivalent level of safety.
4. Roof types excluded from some ventilation or sarking rules: The NCC excludes certain roof types from some specific requirements (for example, concrete roofs or roofs made of structural insulated panels may be exempted from some sarking or ventilation clauses - see NCC Volume One F8D5 notes).

State and Territory Variations

1. The NCC is adopted nationally but each state and territory may modify bushfire provisions through its schedule to NCC Volume One. Examples include:
2. South Australia: SA G5D5 in NCC Volume One prescribes how planning design code bushfire risk categories map to BALs and may assign BAL‑LOW or BAL‑12.5 automatically in certain zones (see NCC Volume One, SA G5D5).
3. New South Wales: NSW G5D3 and NSW G5P2 modify Deemed‑to‑Satisfy and Performance Solution provisions; NSW commonly requires AS 3959 with local amendments and may require referral to the NSW Rural Fire Service for BAL‑FZ or higher risk developments (see NCC Volume One, NSW G5D3 and G5P2).
4. Queensland, Victoria, Western Australia, Tasmania, Northern Territory and the Australian Capital Territory: each jurisdiction publishes a schedule or guidance that may alter BAL mapping or acceptability of Deemed‑to‑Satisfy constructions. Practitioners must check the relevant state schedule in NCC Volume One (Schedules 4-12) and local planning overlays for specific requirements.
5. Note: Always verify against the current edition of the NCC and the jurisdictional schedule because mapping of planning risk categories to BAL and any additional local requirements can change.

Practical Compliance Tips

1. Install sarking/underlay where AS 3959 requires it and ensure it is sealed at ridges, hips, penetrations and eaves to block ember entry; document the product and installation method for the certifier.
2. Balance roof space ventilation with ember protection: follow NCC Volume One Clause F8D5 ventilation free‑area values (e.g., 25,000 mm2/m, 7,000 mm2/m, 5,000 mm2/m) while using mesh or ember guards rated for ember exclusion-do not simply block vents.
3. Use non‑combustible flashings, ridge cappings and penetrations at BAL‑29 and above; where manufacturer instructions differ, provide a fire engineering Performance Solution with supporting testing.
4. Keep roof gutters, valleys and junctions free of combustible debris; design gutters and leaf guards to minimise ember accumulation and allow inspection and maintenance.
5. For existing reroofs, confirm the site BAL first (AS 3959) and if the BAL demands upgraded roof materials or sarking, plan works to meet those requirements rather than relying on like‑for‑like replacement.
6. Record compliance: provide clause and table references in documentation (for example, cite NCC Volume One G5D3 or relevant state G5D clause plus AS 3959 section numbers) so certifiers can quickly verify compliance.
7. Check state schedules and local planning overlays early in design: some jurisdictions map risk categories to minimum BALs (for example SA G5D5, NSW G5D3/G5P2) and may require additional approvals or a Performance Solution for certain building classes.

References: NCC Volume One - Building Code of Australia (G5D3, G5D5, F8D5), NCC Volume Two - Building Code of Australia (H2D8), AS 3959 Construction of buildings in bushfire prone areas, AS 4654 for membrane waterproofing where applicable.

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