You’re halfway through a major commercial design project when someone flags it: “We need to make sure the louvres meet AS 4740:2025.”
Cue the panic.
You open the standards document, flick through the pages—and suddenly you’re knee-deep in technical jargon about water egress, test rigs, and classification charts. All you want to know is: what’s actually changed, and does it mean your current louvre spec is out of date?
You’re not alone. With the release of AS 4740:2025, many architects, builders and procurement managers are trying to get their heads around what the new classification system means and how it affects real-world projects. And let’s be honest—most standard updates feel like they’re written against you, not for you.
Here’s the good news: this one actually gives you more clarity—if you know how to use it.
In this article, you’ll learn exactly what’s changed in AS 4740:2025, what the new louvre classes (A through D) mean, and how to make confident, compliant decisions when specifying louvres for your next project.
AS 4740 is the Australian Standard that sets out how performance louvres are tested and classified based on how well they stop water from getting through.
If you’re dealing with ventilation systems on commercial or industrial buildings, this isn’t just a nice-to-have. It’s essential. Louvres are often installed on walls to let air in while keeping rain out — and when they fail, water gets in, causing damage, safety issues, and compliance headaches.
The key thing to know is: AS 4740 isn’t about aesthetics or airflow alone. It’s about weather resistance, and it’s the benchmark the industry uses to test how louvres perform under simulated wind-driven rain conditions.
Until recently, the standard left some room for interpretation. Now, with the 2025 update, it’s become much clearer — especially around how louvre performance is graded. That clarity helps you avoid vague claims like “high-performance louvre” and instead compare products based on hard data.
So, if you’re specifying louvres on a job and care about durability, leakage, and compliance — you need to know what this standard says.
After 25 years, AS 4740 has undergone significant revisions to enhance clarity, consistency, and performance assessment in louvre design. Here’s a breakdown of the key changes:
The rain resistance classification system has been updated for greater precision:
This refinement ensures a clearer understanding of a louvre’s ability to prevent water ingress, aiding in more accurate product selection.
AS 4740:2025 introduces formal definitions for:
These definitions standardise measurements, facilitating consistent performance assessments across different products and manufacturers.
The standard now provides a clearer definition of the “throat area,” calculated as the sum of the areas between:
This clarity aids in more accurate airflow calculations and performance evaluations.
A new “Extended Range” testing method has been introduced, aligning with international standards such as AMCA-500-L. The updated parameters include:
These enhancements subject louvres to more rigorous conditions, ensuring they can withstand extreme weather scenarios.
The standard refines airflow and pressure measurement techniques, adopting more precise, equation-based approaches. This ensures:
A unified test rig now supports both aerodynamic and rain resistance testing.
This standardization ensures:
AS 4740:2025 now incorporates explicit pressure definitions for wind loading, providing:
Now, after testing a louvre’s ability to resist wind-driven rain, it will be assigned a performance class. This class tells you, at a glance, how effective the louvre is at keeping water out.
Here’s the breakdown:
AS 4740:2025 brings forth comprehensive updates that:
These changes empower architects, engineers, and builders to make more informed decisions when specifying louvres, ensuring compliance with modern performance requirements and resilience against challenging environmental conditions.
On paper, a new classification system might seem like just another tick-box update. But in reality, this change impacts how you design, specify, and justify your louvre choices.
Here’s why that matters:
With clearly defined Classes A to D, you’re no longer relying on vague terms like “weatherproof” or “high-performance”. You know exactly what level of water resistance you’re getting, and more importantly — whether it’s enough for your building’s exposure level and purpose.
For example:
One of the worst outcomes in building design is unexpected water ingress — especially if it leads to mould, corrosion, or system failures. With the new AS 4740:2025 classifications, you can demonstrate that the product chosen was fit for purpose and selected based on measurable criteria, not assumptions.
This is especially important when dealing with:
In short, AS 4740:2025 helps you design with intent, specify with confidence, and defend your decisions if things ever go sideways.
The new classification system is only useful if you know how to apply it. Choosing the right louvre class isn’t just about aiming for the highest rating — it’s about matching performance to real-world conditions and risk levels.
Here’s how to approach it:
Is your project in a high-wind, high-rainfall area? Then you’re dealing with a high risk of wind-driven rain ingress — and you’ll want Class A or B louvres that provide the most protection.
These buildings can’t afford leaks. Water ingress here means equipment failure, downtime, or serious health risks.
Class C or D? More suited to buildings with minimal exposure or where some water ingress is tolerable — for example, car parks, screened areas, or rooms with sloped internal drainage.
Even a small amount of water ingress might be fine in some situations — but in others, it could trigger major costs. Ask yourself:
If the answer is “no” or “we don’t know,” then a lower-class louvre isn’t worth the risk.
Performance testing doesn’t stop at just water resistance. Many louvres are also tested and compared based on additional metrics like airflow (discharge loss coefficient), rain rejection, and overall pressure drop.
Here’s the thing:
Don’t just look at the class — look at the full performance profile.
It’s possible for a Class B louvre to outperform a Class A louvre when it comes to airflow efficiency. If your project demands high ventilation rates or low pressure drop, that trade-off could be critical.
In other words, performance is a balancing act. The updated AS 4740 classifications give you one vital piece of the puzzle — water resistance — but the smartest designs will also factor in airflow and exposure risk to make well-rounded, defensible decisions.
So, selecting a louvre isn’t just about chasing the top rating. It’s about picking the right tool for the job — one that suits your climate, building use, and ventilation goals.
With AS 4740:2025 now in play, you’ve got a clearer framework for choosing louvres that perform the way your building needs them to. But the key is acting on that clarity — not just noting the change and moving on.
Here’s what you should do next:
Look at your current or upcoming projects. Are the louvre specs still based on old performance assumptions? If you’re using product names or models from before 2025, check their newly assigned class — and make sure they still stack up.
When talking to manufacturers or suppliers, be specific:
If they can’t give you that info, that’s a red flag.
Bottom line?
AS 4740:2025 is more than just a standards update. It’s a tool — one that lets you design smarter, spec with clarity, and build with fewer surprises. Use it well.
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