Back to News
After 25 years, AS 4740 - the benchmark standard for performance testing and classifying natural ventilators - has undergone a major revision. Louvreclad played a foundational role in identifying the need for change and leading the update process.
The journey began in 2021 when inconsistencies in the existing standard’s test rig descriptions and procedures were found to produce unreliable results. In response, Louvreclad launched an internal investigation and engaged wind engineering and aerodynamics experts. These efforts culminated in a net benefit proposal submitted to Standards Australia, which ultimately led to the revised AS 4740:2025.
The aim of AS/NZS 4740: 2000 was to provide standardised requirements and performance test methods for natural ventilators for use by manufacturers, suppliers, testers, specifiers, and consumers. Selecting the right louvre profile is crucial to achieving optimal energy efficiency in the building envelope. To make an informed choice, it is essential to have accurate louvre performance data—particularly regarding pressure drop and rain defence—as these factors directly impact the building's thermal performance and overall energy demands. However, ambiguity in test definitions and methods undermined the standard’s value, leading to misinterpretations and inaccurate test data.
AS 4740:2025 addresses these issues head-on, ensuring greater accuracy and consistency through clearly defined testing protocols and performance metrics.
The new standard has been developed in collaboration with Australian manufacturers and consultants via Standards Australia. Louvreclad led the formation of the industry committee with Dr Brendan Gilhome acting as Draft Leader on Louvreclad's behalf. AS 4740:2025 delivers a modernised standard that provides more accurate test data and better reflects how louvres perform for rain resistance and aerodynamics.
1. Clarified Terminology and Diagrams
Definitions for critical terms such as Core Area, Core Velocity, and Throat Area have been clarified. Updated diagrams illustrate how to correctly calculate these values, enhancing interpretation and accuracy.
2. Standardised Testing Rig
A unified test rig now supports both aerodynamic and rain resistance testing, improving measurement repeatability. Clear rig dimension diagrams are included for consistent implementation across test facilities.
3. Extended Test Parameters
• 203 L/h·m² rainfall rate • 22.4 m/s simulated wind velocity • Ventilation rates up to 5 m/s
This extended range brings the AS4740 standard to the highest level of all international standards for testing louvres.
4. Aerodynamic Efficiency – Pressure Drop [Pa] and Discharge Coefficient remains a primary performance metric for classifying louvres.
5. Refined Performance Classifications
Louvre performance is now classified under: • Rain Resistance (Classes A to D) • Discharge Coefficient (Classes 1 to 4) • Wind Loading, with explicit pressure definitions
6. Higher Instrumentation Standards
Improved instrumentation tolerances and broader classification scales help ensure repeatable, reliable results across different facilities and products.
7. Refinements and Updates
Other refinements include a wider classification scale, stricter instrument tolerances, and improved guidance for repeatable testing.
While AS 4740 remains the foundation for louvre testing, the 2025 update encourages design teams to go beyond standardised lab conditions, especially in complex projects.
Louvreclad uses CFD assessments to: • Improve louvre aerodynamic performance (lower pressure drop) • Improve louvre rain resistance • Optimise the design of louvre profiles before fabrication. • Provide project-specific insight
CFD bridges the gap between lab testing and real-world application, supporting projects with project specific climate data and design feasibility studies. Louvreclad is the only company to provide real-world assessments of the louvre installation taking into account project-specific climate conditions, context, and installation details to produce accurate real-world performance assessments.
Louvreclad encourages a risk-based approach, using site geometry, location, orientation, and local climate data to estimate likelihood and extent of water ingress and aerodynamic performance. This supports design decisions for applications such as critical infrastructure projects, smoke control, IT spaces, and high-performance facades, as well as drainage requirements to ensure NCC compliance.
AS 4740:2025 is the most stringent, standardised louvre test regime Australia has seen—driven by Louvreclad and supported by industry experts. It raises the bar for ventilation system design, clarity in performance data, and suitability for real conditions.
This revised standard: • Clarifies key definitions • Standardises testing procedures across all products • Expands test limits to bring it to the highest level, compared to other International Standards • Includes wind load requirements for structural validation • Ensures fairer comparisons with a new single standard test rig
If you are designing and specifying performance louvres for ventilation systems and rain resistance—AS 4740:2025 is your framework for confident, future-ready design.
Explore our full webinar on specifying rain resistance for louvres.
All images and diagrams courtesy of Standards Australia, AS 4740:2025 Natural Ventilators—Classification and Performance.