Wind load is the primary structural action on a building facade. It governs panel selection, fixing design, subframe layout, and span distances. For aluminium cladding and curtain wall systems, understanding how wind pressures are determined - and what test data confirms a product can resist them - is fundamental to getting the facade engineering right.
This article covers how site-specific wind loads are calculated under AS/NZS 1170.2, what the key parameters mean in practice, and how Valmond & Gibson product test data maps to real project requirements.
How are wind loads on facades determined?
AS/NZS 1170.2 (Structural design actions - Wind actions) is the governing standard for calculating wind loads on buildings and structures in Australia and New Zealand. Every facade design starts here.
The standard defines a methodology for calculating design wind pressures at any point on a building’s exterior. The key input parameters are:
Wind region. Australia is divided into non-cyclonic regions (A and B) and cyclonic regions (C and D). The region sets the base wind speed. Region A covers most of southern and inland Australia, while Region B covers parts of the east coast. Regions C and D cover the tropical cyclone belt across northern Australia.
Terrain category. The roughness of the surrounding terrain affects how wind speed varies with height. Open farmland (TC1) produces higher wind speeds at a given height than suburban housing (TC3). The standard defines four terrain categories, from fully exposed to shielded urban.
Building height. Wind speed increases with height above ground level. A panel at 50 metres elevation will experience higher design pressures than the same panel at 10 metres. The standard provides multipliers at each height increment.
Shielding and topography. Nearby buildings, ridgelines, escarpments, and other terrain features can either increase or reduce wind pressures at a given location. The standard accounts for these through shielding multipliers and topographic multipliers.
The output is a set of design wind pressures, expressed in Pascals, for each face and zone of the building. These pressures are what the facade system must resist.
Why do corners and edges matter?
One of the most important details in facade wind load design is the variation in pressure across the building face. Wind does not apply uniform pressure everywhere. Corners, edges, and the tops of buildings experience significantly higher local pressures than the central field areas.
AS/NZS 1170.2 captures this through local pressure factors. These factors increase the design pressure in defined zones near edges and corners, sometimes by a factor of two or more compared to the general field area. The width of these high-pressure zones depends on the building dimensions and the standard’s geometric rules.
This is directly relevant to facade design. A panel system that comfortably resists field-area pressures may need closer fixing centres, stronger subframe members, or a different bracket arrangement near corners and parapets. Ignoring local pressure factors and designing the entire facade to field-area pressures is a common shortcut that creates problems downstream - either during engineering review or, worse, after installation.
Area reduction factors also come into play. Smaller tributary areas (the area supported by a single fixing or bracket) attract higher design pressures than large tributary areas. This means individual fixing points need to be checked for higher loads than the average pressure across the full panel.
What is the difference between SLS and ULS for facades?
Facade systems must satisfy two limit states under the wind loading standard:
Serviceability limit state (SLS). This represents the wind pressures a facade will experience repeatedly during its design life - the conditions it needs to remain fully functional under. At SLS, panels should not deflect excessively, joints should not open, seals should remain intact, and the system should continue to perform its weatherproofing function. The deflection limit under AS/NZS 4284 testing is typically span divided by 150 for the panel between fixing points.
Ultimate limit state (ULS). This represents the extreme wind event - the design capacity against structural failure. At ULS, the system must not collapse, fixings must not pull out, and panels must not detach from the building. Some permanent deformation may be acceptable at ULS, but structural integrity must be maintained.
The ULS pressure is higher than SLS, typically by a factor of around 1.5 depending on the applicable load combination factors. Both conditions must be checked, and the facade system’s test data or engineering calculations need to demonstrate compliance with each.
In practice, SLS often governs the design of aluminium facade panels because the deflection limit controls the allowable span before the strength limit does. This means the maximum distance between fixing points is usually set by how much the panel deflects under service wind, not by how much load it can carry before failure.
How do wind loads relate to panel span and fixing layout?
The relationship between wind pressure and panel span is straightforward: for a given panel profile, higher wind pressures require shorter spans between fixing points to keep deflections within limits.
This is where product test data becomes essential. A facade engineer needs to know, for a specific panel type, what span it can achieve at the project’s design wind pressure while staying within the deflection limit. Reducing the span - bringing fixing points closer together - increases the panel’s wind load capacity but also increases the amount of subframe material and installation labour.
The subframe itself also needs to be designed for the wind loads it collects from the panels. Bracket spacing, member sizing, and connection details all derive from the same wind pressure calculations. The entire load path - from panel face through fixings, through subframe, through brackets, into the primary structure - must be checked for both SLS and ULS.
For unitised curtain wall systems like 165CW, the framing depth and mullion design are integral to wind load performance. The 165mm frame depth of the 165CW system is designed to accommodate the deflection requirements of mid-rise to high-rise applications, with structural members in 6005A-T6 alloy providing the stiffness needed to control mullion deflection under wind load.
What does the V&G test data tell us?
Valmond & Gibson provides independently verified test data for its facade systems, giving facade engineers the information they need to assess product suitability against project-specific wind loads.
interloQ has been weather-tested to AS/NZS 4284:2008 at plus or minus 1500Pa serviceability limit state by Ian Bennie & Associates (NATA accreditation #2371, report 2022-031-S1). This means the interlocking rainscreen system passed air infiltration, water penetration, and structural adequacy testing at 1500Pa positive pressure and 1500Pa negative pressure without exceeding deflection limits or allowing water through.
element13 has the same AS/NZS 4284 weather performance rating - tested to plus or minus 1500Pa SLS (report 2022-031-S2, Ian Bennie & Associates). Beyond this, element13 has also been structurally tested to AS 4040.3 by JFS Engineers (report 23-00156), achieving SLS capacity of 1875Pa and ULS capacity of 5559Pa. That ULS figure is significant - it means element13 solid aluminium panels are rated for cyclonic wind regions, where design pressures exceed what non-cyclonic rated products can handle.
165CW is a unitised curtain wall system designed in accordance with AS/NZS 1170 and conforming to AS/NZS 4284:2008. As a fully engineered curtain wall, 165CW is project-specific in its wind load design - each job gets engineering to match the site’s wind requirements, rather than relying on a single generic test pressure.
What does plus or minus 1500Pa cover in practice?
For projects in wind region A - which covers most of metropolitan Australia outside the tropical cyclone belt - a test rating of plus or minus 1500Pa SLS is adequate for buildings up to approximately 25 metres in height across most terrain categories. This covers a significant portion of the commercial and multi-residential market: four to eight storey buildings in suburban and urban settings.
The exact applicability depends on the specific combination of terrain category, shielding, topography, and local pressure factors at the building’s location. A facade engineer will calculate the precise requirement. But as a general benchmark, 1500Pa SLS provides good coverage for the mid-rise segment.
When higher ratings are needed - taller buildings, cyclone regions B through D, exposed coastal or hilltop sites, or buildings with unusual geometry that generates high local pressures - the design needs to account for that. This is where element13’s AS 4040.3 cyclonic rating (ULS 5559Pa) becomes relevant, or where 165CW’s project-specific engineering approach allows the system to be designed to whatever the wind load analysis demands.
What role does V&G play in the wind load design process?
The facade engineer determines the site-specific wind pressures based on the project location, building geometry, and AS/NZS 1170.2 parameters. V&G provides the product test data and technical information that the engineer uses to confirm the selected system can resist those pressures.
This is an important distinction. V&G is a product supplier, not a facade engineering consultancy. We do not determine wind loads for projects or certify that a system is adequate for a specific building. What we do is ensure our test data is clear, independently verified, and readily available - so the engineers and specifiers making those assessments have what they need to work with.
Our compliance packs include the full test reports, and our team can discuss how the data applies to specific project conditions. If a project’s wind load requirements sit outside the standard test ratings, we can advise on span adjustments, fixing arrangements, or product selection that may achieve compliance - always in coordination with the project’s facade engineer.
Need wind load test data or compliance packs for a project? Talk to our team for technical support and product documentation.
Related Reading
- AS/NZS 4284 Facade Testing Explained
- Subframe Design for Aluminium Rainscreen Cladding
- High-Rise Facade Trends in Australia 2026
- How to Write a Facade Specification for NCC Compliance
Last updated: 4 April 2026