Wind Load Requirements for Roof Structures Under the NCC

What This Requirement Covers

Wind load requirements for roof structures under the National Construction Code (NCC) set the minimum design actions and performance criteria to ensure roofs remain stable, intact and do not endanger people or property during wind events, including cyclonic conditions where applicable. These rules exist to limit structural failure, prevent progressive loss of cladding and fixings (which can become dangerous debris), and ensure continuity of the building envelope so that lives and adjacent structures are protected.

The requirements apply to designers, structural engineers, certifiers, builders and manufacturers involved in the design, selection and installation of roof framing, roof cladding, flashings, gutters, battens, fixings and connections. Application depends on building class, location (wind region), importance level, and whether the building is in a cyclonic area - with specific additional tests and provisions for metal roof cladding and assemblies in cyclonic regions as set out in the NCC.

Key Requirements

1. Wind actions must be determined in accordance with AS/NZS 1170.2 (Structural design actions - Wind actions) and incorporated into structural design as specified in NCC Volume One, Part B1 and associated parts (see WA variations where applicable). (See: NCC Volume One, Part B1 - Determination of individual actions and AS/NZS 1170.2.)
2. The ultimate limit state wind pressure, Pt, used for cladding testing and design is calculated in accordance with AS/NZS 1170.2, modified where required by variability factors from AS/NZS 1170.0 Table B1 (refer NCC Volume One and Volume Two references to Pt). (See: NCC Volume One S4C2, Table S4C2 notes.)
3. For Class 1 and 10 buildings and other housing, where AS 4055 (Wind loads for housing) applies, wind classification and design pressures must be assigned using AS 4055:2021 where permitted by the NCC Housing Provisions. (See: NCC Volume One - Schedule of referenced documents; NCC Volume Two H1 series.)
4. In cyclonic areas (wind regions B2, C and D per AS/NZS 1170.2 or local schedule definition), additional design and testing requirements apply: metal roof cladding and immediate supporting members, connections and fixings must resist low-high-low fatigue pressure sequences A to G as specified in Specification 4 (Design of buildings in cyclonic areas) and Table S4C2 (NCC Volume One / Volume Two). The sequence prescribes cycles and magnitudes (for example Sequence D: 1 cycle 0 to 1.0 Pt; Sequences A and G: 4,500 cycles 0 to 0.45 Pt, etc.). (See: NCC Volume One S4C2; Table S4C2.)
5. Roof cladding testing and acceptance criteria: a cladding assembly must remain in position notwithstanding any permanent distortion, fracture or damage under the specified pressure sequence. If a system fails the fatigue loading sequence in Table S4C2 (or H1D7/H1D8 test requirements for housing), it does not comply. (See: NCC Volume One S4C2 and NCC Volume Two H1D7 explanatory information.)
6. Design actions must consider building Importance Level (from Table B1D3a) when selecting annual probability of exceedance and the corresponding wind actions per AS/NZS 1170.2 (NCC Volume One WA B1D3). Important structures (higher importance levels) require greater design reliability. (See: NCC Volume One WA B1D3.)
7. For structural members and connections, design wind pressures are applied and member design should follow relevant structural standards such as AS 4100 (Steel structures), AS 1720.1 (Timber structures) and AS 1684 (Residential timber-framed construction) where applicable. Where masonry elements interface with roofs, AS 3700 applies for masonry design.
8. Specific measurements and thresholds to include in design calculations (examples - to be derived per project using AS/NZS 1170.2 and AS 4055 where applicable):
9. Peak external pressure values (Pt) in kPa - calculated from wind region, terrain/height factors, shielding, topography and importance level using AS/NZS 1170.2 (values vary widely by site and must be calculated, not assumed). (See: AS/NZS 1170.2 and NCC Volume One references.)
10. Fatigue test sequences for cyclonic roof cladding per Table S4C2: Sequence A - 4,500 cycles 0 to 0.45 Pt; B - 600 cycles 0 to 0.6 Pt; C - 80 cycles 0 to 0.8 Pt; D - 1 cycle 0 to 1.0 Pt (held minimum 10 seconds in some tables); E - 80 cycles 0 to 0.8 Pt; F - 600 cycles 0 to 0.6 Pt; G - 4,500 cycles 0 to 0.45 Pt. (See: NCC Volume One Table S4C2.)
11. Where housing provisions apply, reference to AS 4055:2021 provides simplified pressure tables and wind classifications (including town/terrain/height modifiers) for Class 1 and 10 buildings - use only where permitted and check state housing provisions. (See: NCC Volume One - Schedule of referenced documents; NCC Volume Two H1 provisions.)

Relevant clauses and documents (examples of required citation)

1. NCC 2022 Volume One - Part B1: WA B1D3 Determination of individual actions (wind actions and importance levels). (See: NCC Volume One, Part B1/WA B1D3.)
2. NCC 2022 Volume One - Specification 4: Design of buildings in cyclonic areas and Table S4C2 low-high-low pressure sequence. (See: NCC Volume One S4C2; Table S4C2.)
3. NCC 2022 Volume Two - H1D7 and explanatory information for metal roof cladding testing in cyclonic areas. (See: NCC Volume Two H1D7.)
4. AS/NZS 1170.2 - Structural design actions - Wind actions (design wind pressures and procedures). (See: AS/NZS 1170.2.)
5. AS 4055 - Wind loads for housing (where permitted by NCC Housing Provisions). (See: NCC Volume One schedule and Volume Two H1 series.)
6. AS 1684 - Residential timber-framed construction; AS 4100 - Steel structures; AS 3700 - Masonry structures - for member and connection design against wind loads.

Residential vs Commercial

1. Residential (Class 1 and 10) buildings often use the simplified wind loading procedure in AS 4055 when the NCC Housing Provisions allow its use. AS 4055 gives wind classifications (e.g., N1, N2, C1, C2, up to cyclone regions) and corresponding design pressures useful for typical houses, carports and outbuildings. In cyclonic wind regions the full AS/NZS 1170.2 methodology and Specification 4 cladding testing requirements will apply. (See: NCC Volume Two H1 provisions; AS 4055.)
2. Commercial and larger buildings (Class 2-9) generally must use the full AS/NZS 1170.2 design process to derive site-specific Pt values, factoring in building size, height, terrain category, shielding, topography and importance level. Structural framing, connections and cladding must be designed and detailed to resist these calculated pressures using AS 4100, AS 1684, AS 1720.1 and other applicable standards. Cyclonic-area additional requirements (Specification 4 and Table S4C2) also apply where the building is in a cyclonic region. (See: NCC Volume One Part B1; AS/NZS 1170.2.)

Exceptions and Exemptions

1. Use of AS 4055: Small domestic Class 1 and 10 buildings may use AS 4055 instead of AS/NZS 1170.2 where allowed by the NCC Housing Provisions. This is a limited simplification and is not appropriate for complex or large roof forms. (See: NCC Volume One schedule and Volume Two H1.)
2. Cyclonic testing exceptions: there are no general exemptions from Specification 4 for roof cladding in cyclonic areas - metal cladding assemblies must pass the fatigue sequence testing in Table S4C2. Alternative compliance may be demonstrated by testing or by using tested proprietary systems that are certified to meet the sequences. (See: NCC Volume One S4C2; NCC Volume Two H1D7.)
3. State schedules or WA variations may alter or add requirements for certain wind regions - designers must check the relevant state schedule in the NCC 2022 Volume One Schedules 4-12 for any local variations. (See: NCC Volume One schedule notes.)

State and Territory Variations

1. The NCC includes state and territory schedules which can modify wind-related provisions. For example, Western Australia includes variations to the determination of wind actions and identifies cyclonic areas and wind region definitions in WA Part B2 and related WA B1D3 clauses. WA also explicitly references modifications to AS/NZS 1170.2 and AS 4055 in its schedule. (See: NCC Volume One WA B1D3; Schedule of referenced documents.)
2. Queensland, Northern Territory and other states with tropical/coastal zones may have specific schedule references or requirements for cyclone-prone areas - always verify against the relevant state schedule in the NCC Volume One Schedules. (See: NCC Volume One Schedules 4-12.)
3. Builders and designers must check local planning and state legislation as some states adopt additional or alternative detailing, testing or certification requirements for roof cladding and connection systems.

Practical Compliance Tips

1. Use the correct wind standard for the job: confirm whether AS 4055 (housing) is permitted for your Class 1/10 project or whether AS/NZS 1170.2 is required for a site-specific design.
2. Determine the building Importance Level early and use it in the wind action calculations - this directly affects Pt and design pressures (NCC Volume One, Part B1 references).
3. For projects in wind region B2, C or D (cyclonic regions), specify tested cladding assemblies or ensure roof systems are proven to resist the Table S4C2 fatigue sequence - do not rely on untested details.
4. Document all assumptions (terrain category, shielding, topography, height, importance level) and reference the specific NCC clauses and AS standards used (e.g., AS/NZS 1170.2, AS 4055, Specification 4). Certifiers expect clear traceability to the code and standards.
5. Pay attention to fixings and immediate supports: failure often starts at fixings or battens. Use manufacturer-tested fixing schedules or detail connections per AS 1684 / AS 4100 and supplier literature validated to the relevant wind classification.
6. Avoid generic pressure values. Calculate Pt for the site using AS/NZS 1170.2 (or AS 4055 where allowed) rather than using rule-of-thumb pressures - small geometry or terrain changes can materially change design pressures.
7. Check state schedules and local authority requirements early (for example WA variations to AS/NZS 1170.2 and AS 4055) to ensure any additional provisions are included in the design and documentation.

Citations and references in the NCC context include: NCC 2022 Volume One - Part B1 (Determination of individual actions / WA B1D3), Specification 4 and Table S4C2 (low-high-low pressure sequence), NCC 2022 Volume Two H1D7 (cladding testing in cyclonic areas), AS/NZS 1170.2 (Wind actions), AS 4055 (Wind loads for housing), AS 1684, AS 4100 and AS 3700 where applicable.

Note: Wind pressures and member capacities are site and design specific. The NCC and referenced Australian Standards must be followed to produce accurate numerical values for any particular project. If documentation is unclear for a specific situation, confirm details with a registered structural engineer or building certifier and check the relevant state schedule in NCC 2022 Volume One for variations.