How do I choose the right louvre for my project?

Louvres can serve several purposes within a building, from providing ventilation and protecting openings from wind-driven rain to screening plant and equipment from view. With different applications requiring different levels of performance, selecting the highest-performing louvre is not always necessary.

This article looks at how louvre performance is classified, what the different ratings mean and why the intended application should determine the system selected.

How is louvre performance measured?

Weather louvres are tested to BS EN 13030 for both rain rejection and aerodynamic performance. Rain rejection is classified from Class A to Class D, with Class A providing the highest level of protection (99–100% effectiveness). However, performance varies with airflow velocity, so the classification should always be considered alongside the project's design airflow requirements. A Class A rating also does not mean the louvre is completely watertight under all conditions.

Aerodynamic performance is classified separately from Class 1 to Class 4, with Class 1 offering the lowest resistance to airflow. As features that improve rain defence can also increase airflow resistance, louvre selection should balance weather protection with the required ventilation performance.

Acoustic louvres are tested for sound attenuation as well as airflow performance. Under BS EN ISO 10140-2, acoustic performance is measured using the Sound Reduction Index (SRI) in decibels, with a Weighted Sound Reduction Index (Rw) sometimes used as an overall rating.

Does every project need Class A?

A Class A classification does not necessarily make a louvre more suitable for every project.

Where louvres protect ventilation openings or sensitive plant and equipment from wind-driven rain, a high level of rain defence may be essential. In these applications, the required classification should be considered alongside the volume and velocity of air passing through the system.

However, not all louvres are required to provide weather protection. Where a louvre is used primarily as an architectural screen to conceal rooftop plant, service areas or other equipment, preventing rain penetration may not be necessary.

Other applications may have different priorities. For example, acoustic louvres are designed to reduce the transmission of noise from mechanical plant and ventilation systems, making acoustic performance a key consideration alongside airflow.

Specifying for the application

Choosing the right louvre starts with understanding what the system needs to achieve. Rain defence, airflow, screening and acoustics are different performance requirements, and their importance will vary between projects.

For example, a high-performance ventilation louvre may achieve Class A rain defence at a specified airflow velocity while providing relatively low resistance to airflow. A screening louvre, by comparison, may not require a high level of weather protection but can still provide the visual screening required.

Acoustic louvres have a different performance profile again. Their deeper construction and acoustic infill are designed to reduce noise transmission, but can increase resistance to airflow. Selecting a louvre with greater airflow resistance than required could increase pressure drop across the system and affect ventilation performance.

Understanding the ratings and the conditions under which they are achieved allows project teams to select a system that provides the required level of performance without over-specifying.