AS/NZS 1170.2:2021 for Solar Mounting: How the Wind Number Is Built

AS/NZS 1170.2 wind regions, regional speeds and roof loads.

An Australian solar wind assessment starts with two inputs: the site’s wind region and the regional wind speed for the required annual probability of exceedance. Those inputs establish the wind climate. Terrain, height, direction and topography then determine site exposure; array geometry determines pressure; the mounting layout transfers that pressure into the roof or foundation.

This guide follows that sequence for EPCs, installers and project engineers. It explains how to use a wind-region map and wind-speed table, what changes between rooftop and ground arrays, and what a reviewable mounting proposal should contain. AS/NZS 1170.2 supplies wind actions. It does not, by itself, certify the capacity of a solar mounting system.

1. Locate the project on the Australian wind-region map

The current classification separates non-cyclonic A0 to A5 and B1 from cyclonic B2, C and D. B1 and B2 share regional-speed values, but their climate and component provisions differ. Island allocations also matter: the amended map identifies Norfolk Island, Christmas Island and the Torres Strait Islands as B2, Cocos Islands as C, and Lord Howe Island as A2. Source: amended regional map and Table 3.1(A)

Under the 2021 framework, Australia includes the A subregions, B1, B2, C and D. The distinction between B1 and B2 matters: an old calculation labelled simply “Region B” needs a fresh location check before its inputs or mounting spacings are reused. The 2021 revision also introduced A0 and revised regional boundaries and directional treatment. Research and revisions in AS/NZS 1170.2:2021

Use coordinates, not only a suburb or state name. Near a regional boundary, retain a record of how the location was resolved. Where coastal-distance rules apply, use the Standard’s defined coastline and distance method; a distance measured casually from a beach or estuary can select the wrong input.

The geographic region remains only one part of the assessment. An exposed industrial roof and a sheltered low building in the same region can have different site speeds and fixing reactions. Hills, escarpments, height and approach terrain must be assessed separately.

2. Read the regional wind-speed table correctly

Table 1. Selected Australian regional wind speeds in m/s

Reference basis: AS/NZS 1170.2:2021, including Amendments 1:2023 and 2:2024; Table 3.1(A). R is the average recurrence interval in years.

Source: AS/NZS 1170.2:2021, Table 3.1(A), printed page 25. Selected rows, independently checked against the published values. These are regional peak-gust values, with an equivalent moving-average time of approximately 0.2 seconds. They are not directly interchangeable with a 3-second-gust rating from another wind standard. Values precede climate, direction and site adjustments. The table is a regional reference; it is not a mounting-capacity table.

C and D are maximum regional values. Apply the Standard’s coastal-distance interpolation for the exact location: C between its maximum and B2, D between its maximum and C maximum. Do not assign 66 m/s or 80 m/s to every site in C or D solely because those values appear in the 1/500 row.

In this publication set, M_c = 1.0 for A0 to A5 and B1, and M_c = 1.05 for B2, C and D. It is applied separately from V_R. For example, B2 at R = 500 has V_R = 57 m/s; V_R × M_c = 59.85 m/s, still before direction and site effects. Climate multiplier: Table 3.3

Select the required annual probability of exceedance before selecting a speed. It depends on the structural design basis, including the importance level and limit state. A value associated with 1/500 annual probability is often described as a 500-year return-period value. It does not mean that the event happens regularly once every 500 years or cannot happen during the project life.

For solar attached to an existing building, confirm the host structure’s design basis and the requirements of the proposed works. The module warranty period or a supplier’s catalogue assumption does not establish the appropriate probability for the building attachment. Serviceability and ultimate checks can require different inputs. AS/NZS 1170.2 publication text

Keep three quantities separate:

• Regional wind speed, V_R: the regional-climate value selected from the relevant map and probability.
• Site wind speed, V_sit,β: the regional value modified for the applicable site conditions and wind direction.
• Design wind speed, V_des,θ: the speed selected for the structure’s design direction under the Standard’s directional procedure.

A “50 m/s” product rating is therefore incomplete without identifying which speed it represents and the geometry, coefficients and limit state behind it. Do not insert a regional table value directly into a pressure calculation while silently omitting the site assessment. Likewise, do not apply a multiplier twice if a supplied project speed already incorporates it.

3. Record the edition and Australian compliance basis

The publication framework discussed here is AS/NZS 1170.2:2021 with Amendment 1:2023 and Amendment 2:2024. The project’s applicable requirements also depend on the adopted National Construction Code edition, the relevant state or territory provisions and the agreed design specification. Record those items together; publication history alone does not establish the applicable project basis.

Western Australia provides a useful example. Its published NCC 2022 state variation gives specific treatment to design wind speeds in Region D. This illustrates why a national map or a calculator’s default edition cannot replace the jurisdictional check. It is an example of a published variation, not a statement that every Australian jurisdiction currently uses NCC 2022. WA Government: NCC 2022 state variation for wind Region D

Keep the edition, amendments, NCC basis and jurisdiction on the calculation cover sheet. For retrofit work, identify any difference from the original roof design. A change of standard does not automatically establish that the roof is inadequate, but an old mounting schedule cannot be assumed to cover a new assessment without review.

4. Convert regional speed into site wind and pressure

The 2021 framework separates the regional climate from site exposure:

V_sit,β = V_R × M_c × M_d × M_z,cat × M_s × M_t

The design-direction procedure then establishes V_des,θ. A general pressure expression is:

p = 0.5 × ρ_air × V_des,θ² × C_shp × C_dyn

Here, the aerodynamic shape and dynamic-response terms belong to the selected calculation method. Their definitions, signs and any applicable factors must be taken from that method. AS/NZS 1170.2 publication text

Terrain assessment extends beyond the property boundary. Open water, farmland and built-up surroundings produce different exposure, and the controlling direction may cross more than one terrain type. Do not rely on a satellite image centred tightly on the roof. Building height also needs a defined reference: it is not interchangeable with site elevation above sea level.

Vegetation is not a substitute for qualifying building shielding. Trees can change with pruning, storms or redevelopment, while the Standard’s shielding provisions have defined structural criteria. Hills and escarpments require a separate topographic check even where the regional classification appears modest.

The square of wind speed explains why these inputs matter. At an illustrative air density of 1.2 kg/m³, increasing design speed from 40 m/s to 50 m/s increases basic velocity pressure from 0.96 kPa to 1.50 kPa: approximately 56%. These are velocity pressures before the relevant aerodynamic coefficients, not panel design pressures or mounting capacities.

5. Select the solar provision that fits the geometry

The array’s mounting arrangement determines the appropriate aerodynamic route. Under the 2021 framework and its published amendments, the principal solar provisions are B.6.1, B.6.2 and B.6.3. Check their complete scope before using coefficients. A familiar roof type or mounting product name is not enough to demonstrate applicability. AS/NZS 1170.2, Appendix B and Amendment 2

B.6.3 is particularly relevant to commercial rooftops, but it is not a universal flat-roof coefficient table. Separate two tasks. First, verify the clause scope and aerodynamic inputs: building and roof geometry, panel dimensions and tilt, layout, clearances, placement, zoning and effective area, as applicable. Second, complete the additional project structural checks: panel reactions, support capacity and the underlying roof’s combined demand.

For ground arrays, wind pressure must be resolved into frame and foundation actions, including uplift, lateral force, bending and overturning where relevant. Soil resistance and pile capacity are separate from the aerodynamic calculation. Trackers, flexible systems or unusual arrangements need an assessment appropriate to their behaviour.

For tilted panels, retain both vertical and horizontal force components. A design described only as “uplift resistance” can leave connection shear or frame response unexplained.

6. Carry the load through every connection

Panel net pressure and pressure across the building envelope are separate quantities. Convert panel loads into support reactions, then assess the supporting roof under the applicable combined load cases. Identify the sign convention, loaded area and coefficient basis for each check so that pressures or local factors are not counted twice.

For example, a uniform net pressure of 1.5 kPa acting normally over a 2.0 m² panel gives a 3.0 kN resultant. It does not mean that every roof foot carries 3.0 kN. Nor does it justify dividing the force equally among four feet without a structural model. Reactions depend on spans, cantilevers, stiffness, eccentricity, restraint and load distribution.

Trace the actual system: module frame and clamps, rails or direct attachments, brackets, fasteners, roof deck or cladding, secondary supports, primary structure and foundations. A tested rail does not establish the pull-out capacity of a screw in a different substrate, or the remaining capacity of an existing purlin.

Three kinds of local condition deserve explicit coverage: building edges and corners; array perimeter panels and exposed row ends; and structural discontinuities such as rail ends or changes in support spacing. They are related checks, but their zones and factors are not interchangeable.

Provide a pressure and reaction schedule covering every applicable roof and array zone. A uniform fixing spacing can be used where the design demonstrates that it satisfies all relevant zones and load cases. The problem is missing verification. Changing from portrait to landscape also requires review because clamp positions, spans and the distribution of support reactions can change.

Amendment 2 notes that PV can increase total wind loading on the underlying roof and that this interaction is outside the Standard’s coverage. Where relevant, the roof assessment needs an adequately supported method. Arbitrarily adding unrelated peak pressures is not a substitute for defining compatible load cases and a justified conservative envelope. AS/NZS 1170.2, B.6.3

7. Review cyclonic provisions and legacy calculations

In B2, C and D, check the requirements that apply to the actual component category. Clause 3.3 requires M_d = 1.0 for cladding and its immediate supporting structure. The responsible designer should determine whether and how that category applies to the proposed PV components; it should not be assigned to every bracket by assumption. AS/NZS 1170.2, Clause 3.3

The design brief should separately record applicable code requirements and broader project checks. These can include envelope breach and internal pressure, windborne debris exposure, cyclic loading or fatigue, corrosion and installation quality. Not every B2 project has the same test requirements. A single static load test does not establish the performance of the complete roof assembly under every cyclonic condition.

Before reusing a spreadsheet or spacing table, check its source inputs and assumptions against the selected edition. The Amendment 2 control list includes the Australian wind-region figure and regional wind-speed table, as well as pressure provisions and the new B.6.3 route. Recheck those items instead of assuming that only the solar section changed. This does not mean that every region’s speed increased or every boundary moved. Amendment control record

Also review changed module size, array tilt, edge distance, roof height, substrate and support spacing. A calculation can be unsuitable because the project changed even when its wind-standard edition remains acceptable.

8. Prepare the information for a mounting review

Start with the site location, roof or ground arrangement, module layout and available design basis. Identify uncertain inputs explicitly so that the proposal does not conceal them behind a single wind-speed rating.

Keep the final installation drawing consistent with the calculations. It should identify the permitted spacing and cantilevers, applicable zones, fastening requirements and any restrictions on substitution. Product test evidence should match the load direction, component arrangement and substrate being relied upon. If a required input remains unverified, state what must be resolved before that part of the design can be accepted.

This article explains the design process. Use the applicable Standard, amendments and jurisdictional requirements for project calculations and have the complete structural design assessed by a suitably qualified engineer.

For projects across the Tasman, see Wind design for solar mounting in New Zealand. For the ASCE 7 basis, see ASCE 7-22 for solar mounting. For a general checklist, see Solar PV design in high wind areas.

Frequently asked questions

Is a “rated to 50 m/s” product statement enough to approve a mounting system?

No. The rating is incomplete without identifying which speed it represents (regional V_R, site V_sit,β or design V_des,θ) and the geometry, coefficients and limit state behind it. A regional table value cannot go straight into a pressure calculation with the site assessment left out.

Can I assign 66 m/s or 80 m/s to every site in Region C or D?

No. The C and D values in Table 1 are maximum regional values. Apply the Standard’s coastal-distance interpolation for the exact location: C between its maximum and B2, D between its maximum and the C maximum.

What is the difference between Region B1 and Region B2?

B1 and B2 share regional-speed values, but their climate and component provisions differ. B1 is non-cyclonic; B2 is cyclonic. In this publication set, M_c = 1.0 for A0 to A5 and B1 and M_c = 1.05 for B2, C and D, and in B2, C and D the Clause 3.3 requirements for cladding and its immediate supporting structure need to be checked. An old calculation labelled simply “Region B” needs a fresh location check before its inputs or mounting spacings are reused.

Does a 1/500 annual probability mean a 500-year return period?

A value associated with 1/500 annual probability is often described as a 500-year return-period value. It does not mean the event happens once every 500 years or cannot happen during the project life. Select the probability from the structural design basis, including importance level and limit state, not from the module warranty period or a supplier’s catalogue assumption.

Which solar clause applies: B.6.1, B.6.2 or B.6.3?

The array’s mounting arrangement determines the route, and every geometric and other scope condition has to be checked before coefficients are used. B.6.3 is relevant to commercial rooftops but is not a universal flat-roof coefficient table. Clause applicability and the project structural checks (panel reactions, support capacity, the roof’s combined demand) are two separate tasks.

Can an old spreadsheet or fixing-spacing table be reused on a new project?

Only after its source inputs and assumptions are checked against the selected edition. The Amendment 2 control list includes the wind-region figure and regional wind-speed table as well as pressure provisions and the new B.6.3 route. Module size, array tilt, edge distance, roof height, substrate and support spacing also need review, because a calculation can be unsuitable when the project changed even if the wind-standard edition remains acceptable.

References and further reading

• Standards Australia and Standards New Zealand, AS/NZS 1170.2:2021 publication preview, including amendment records.
• Ginger and Holmes, Research and revisions in AS/NZS 1170.2:2021.
• WA Government, NCC 2022 state variation for wind Region D.
• ABCB, NCC 2025 preview, Figure 2.2.3. Map cross-check only; confirm code adoption separately for the project.
• Calcs.com, Wind load calculation to AS/NZS 1170.2:2021. Further reading on the calculation sequence; select project inputs from the applicable source and edition.

Be Supported.