Fire Safety Requirements for Outdoor Decks in Bushfire Areas

What This Requirement Covers

This requirement addresses the fire safety measures that apply to outdoor decks, verandahs and similar external elevated platforms located in bushfire-prone areas in Australia. It exists to reduce the risk of ember ignition, radiant heat damage and flame contact from a bushfire so that attached buildings and occupants have a better chance of remaining tenable and undamaged. The rules draw on the National Construction Code (NCC) bushfire provisions and related Australian Standards that set construction materials, separation distances and detailing required at different Bushfire Attack Levels (BAL).

These provisions apply to buildings and associated Class 10a elements (decks and verandahs) in designated bushfire-prone areas. They are relevant to designers, certifiers, builders and homeowners when designing, constructing or renovating decks that are adjacent to or connected with Class 1 (houses), Class 2-9 buildings, or Class 10 ancillary structures where the site has an assessed BAL under AS 3959-2018 or the relevant state schedule in the NCC Volume One. Compliance may be achieved by following the NCC Deemed-to-Satisfy provisions, applicable state/territory schedules, or by an assessed Performance Solution where required.

Key Requirements

1. Bushfire Attack Level (BAL): Deck requirements depend on the site BAL assessed in accordance with AS 3959-2018 Construction of buildings in bushfire-prone areas and as referenced in the NCC (for example, NCC Volume One, Part G5/G5D clauses). Typical BALs: BAL-Low, BAL-12.5, BAL-19, BAL-29, BAL-40, BAL-FZ. Deck construction and materials requirements increase with higher BAL.
2. Application to building classes: The Deemed-to-Satisfy bushfire provisions in NCC Volume One apply to Class 2 and Class 3 buildings, Class 4 parts, and Class 10a buildings or decks immediately adjacent or connected to those buildings, subject to state schedules (see NCC Volume One, G5D2/G5D3/G5D5). Where a deck is adjacent to a Class 1 building, reference is made to NCC Volume Two and the applicable state provisions for Class 1 buildings in bushfire-prone areas.
3. Materials and non-combustibility at higher BALs: For decks attached to buildings in higher BAL ratings, combustible materials may be restricted. AS 3959 requires non-combustible or specific tested materials for elements likely to be exposed to ember attack and radiant heat at nominated BALs. For example:
4. BAL-19 and above: Increased restrictions on combustible external elements and the use of ember-resistant construction; combustible decking and skirtings are discouraged and may be required to be replaced with non-combustible alternatives depending on design and exposure (see AS 3959-2018 Sections and construction tables).
5. Separation and defensible space: The NCC and state planning instruments reference separation from classified vegetation and asset protection zones. Required separation distances and the determination of BAL are made using AS 3959-2018 and relevant state planning guidance (NCC Volume One, Schedules/State clauses such as SA G5D5 and NSW G5D3/G5D2).
6. Attached elements and junctions: Junctions between the deck and the building must limit ember entry and flame propagation to the building fabric. This includes sealing gaps, preventing accumulation of combustible debris under decks, and protecting intersections with fire-resistant or non-combustible materials in accordance with AS 3959 and NCC bushfire clauses.
7. Elevation and underfloor enclosure: Enclosed subfloor spaces beneath decks can create a combustible void. Where enclosure is proposed in a bushfire-prone area, materials and construction must comply with BAL-related requirements in AS 3959-2018 and the NCC clauses that apply to Class 10a elements connected to buildings (see NCC Volume One, G5D2/G5D3 as applicable).
8. Balustrades, handrails and screens: These components, if combustible, are subject to the same BAL-based restrictions as other external elements. They should be constructed from materials that reduce ember ignition risk and not trap debris against building fabric (refer AS 3959 and NCC bushfire clauses).
9. Referenced standards and clauses:
10. NCC Volume One - Part G5 (Bushfire) and state schedules (e.g., NSW G5D2/G5D3, SA G5D5) - application and Deemed-to-Satisfy provisions for buildings and decks in bushfire-prone areas.
11. NCC Volume Two (where relevant for Class 1 buildings) - see bushfire related sections in Volume Two (e.g., state amendments and H7/H sections where referenced).
12. AS 3959-2018 Construction of buildings in bushfire-prone areas - BAL assessment method and construction requirements for external elements.
13. Where structural design is involved, use relevant standards for framing and fixings such as AS 1684 (timber framing), AS 4100 (steel structures), and AS 3700 (masonry) as applicable for non-fire structural design, but note that fire performance and material combustibility are governed by AS 3959 and NCC bushfire clauses.
14. State schedule notes: Several states have specific schedules inserted into NCC Volume One that modify application or provide specific BAL assignment rules (for example, SA G5D5 and NSW G5D2/G5D3). Always check the state schedule in NCC Volume One for jurisdictional variations.

Residential vs Commercial

1. Residential (Class 1 and associated Class 10a decks): For standalone houses and their decks, bushfire requirements are determined principally by the site BAL under AS 3959-2018, with guidance and Deemed-to-Satisfy provisions in NCC Volume Two and the NCC state schedules. Class 1 decks attached to dwellings typically follow the AS 3959 construction tables for external elements and ember protection measures. If a dwelling is in a designated bushfire-prone area, BAL assessment and appropriate material choices for decking, stair treads, balustrades and under-deck enclosures are required.
2. Commercial and multi-residential (Class 2-9 and decks adjacent to these buildings): The Deemed-to-Satisfy provisions in NCC Volume One, Part G5 apply directly to Class 2, 3, 4 parts and Class 10a elements immediately adjacent or connected to those building types (see NCC Volume One, G5D2). For Class 2-9 buildings, there may be more stringent performance expectations for occupant tenability, access for firefighting and water supply, and therefore decks connected to these buildings must meet the specific NCC Volume One bushfire requirements in conjunction with AS 3959. Where a Class 9 special fire protection purpose building is involved, additional specification references (e.g., Specification 43) may apply as noted in state amendments (see NSW Volume One notes).

In short, the same BAL-based construction approach applies across building classes, but the NCC Volume One provisions apply directly to Class 2-9 buildings while Class 1 buildings use Volume Two guidance plus relevant state rules; Class 2-9 projects often require stricter performance solutions for firefighter access and services.

Exceptions and Exemptions

1. BAL-Low: Where a site is assessed as BAL-Low, houses and decks are generally not required to adopt the elevated construction measures specified for higher BALs, though good practice ember protection is still recommended (see AS 3959 and NCC guidance).
2. Performance Solutions: If the Deemed-to-Satisfy provisions do not suit the project (for example, for buildings at BAL-12.5 with particular constraints), a Performance Solution under the NCC may be used. The Performance Solution must demonstrate equivalence to the Performance Requirements, referencing documented analysis, testing or expert judgment (NCC Volume One Part A performance provisions and Part G5 where applicable).
3. State-specific exemptions: Some states provide alternative BAL assignment or specific exemptions in their NCC schedules (for example, variations for urban interface mapping in SA G5D5 or NSW amendments). These are not national exemptions and must be checked in the applicable state schedule in NCC Volume One.
4. Retrofitting and minor works: Minor repairs or small additions may be managed with proportionate measures rather than full reconstruction to a higher BAL standard, but the certifier or building surveyor must confirm compliance path; an engineering or fire-safety assessment may be needed.

State and Territory Variations

1. New South Wales (NSW): NSW inserts amendments in NCC Volume One (see NSW G5D2, NSW G5D3) that apply Deemed-to-Satisfy provisions to Class 2, 3 and certain Class 10a buildings and decks up to BAL-12.5. For BALs above BAL-12.5, a Performance Solution or specific consent conditions often apply, and NSW references Planning for Bush Fire Protection for some details (NCC Volume One, NSW G5D2/G5D3).
2. South Australia (SA): SA includes a schedule (SA G5D5) that clarifies BAL assignment for areas in the Planning and Design Code, specifying when BAL-Low or BAL-12.5 apply for identified urban interface and risk categories (NCC Volume One, SA G5D5).
3. Other jurisdictions: All states and territories have schedules in NCC Volume One (Schedules 4-12) that may modify or add provisions. The NCC notes that state schedules may change BAL assignment, acceptable construction practices or reference to planning documents. Always verify the state schedule that applies to the site in NCC Volume One and any local planning instruments or bushfire planning guides (for example, Planning for Bush Fire Protection in NSW).

Practical Compliance Tips

1. Assess and document the BAL early: Commission a BAL assessment to AS 3959-2018 before designing the deck so material selection and detail design are correct from the start.
2. Use non-combustible or ember-resistant decking materials at higher BALs: Where the BAL requires it, choose non-combustible or tested ember-resistant decking, and avoid timber that readily ignites unless specifically permitted by the applicable AS 3959 construction table.
3. Prevent debris accumulation under decks: Provide sloping, clearance and either screened ventilation or non-combustible under-deck finishes so embers or leaves cannot accumulate and ignite (seal gaps at the base of the external wall where the deck meets the building).
4. Seal junctions and openings: Ensure all gaps between deck and building, wall penetrations and underfloor cavities are sealed or protected with non-combustible materials to reduce ember entry per AS 3959 guidance.
5. Choose balustrade and screening details that do not trap embers: Avoid recessed or hollow detailing that collects debris; use fine-mesh, non-combustible screens where required and locate combustible fixtures away from critical junctions.
6. Refer to both NCC and state schedules: Always check NCC Volume One (Part G5 and the relevant state schedule) and AS 3959-2018 for the jurisdictional requirements that apply to the site rather than relying on a single national summary.
7. Engage certifiers early for retrofit works: For renovations or retrofitting existing decks in bushfire-prone areas, discuss the proposed measures with the certifier to determine whether a full upgrade to a higher BAL construction standard is required or whether a Performance Solution is acceptable.

References: NCC Volume One - Part G5 and relevant state schedules (e.g., NSW G5D2/G5D3, SA G5D5); NCC Volume Two bushfire sections as applicable; AS 3959-2018 Construction of buildings in bushfire-prone areas; AS 1684, AS 4100, AS 3700 for structural design where relevant.

Could not determine precise page-level clause permutations for every state variation from the retrieved excerpts, so confirm final clause citations in the NCC 2022 Volume One/Two and AS 3959-2018 applicable to your state for certification-level documentation.