When specifying drainable ventilation louvres, one of the most important distinctions is between single-stage and multi-stage systems. Understanding this difference can help ensure consistent rain-defence performance.

A single-stage drainable louvre relies on a single line of defence. Rain impacts the blade, sheds off the face, and any captured water is directed into blade gutters or side channels, then drained out through the sill below.

This is a significant improvement over non-drainable louvres, as water is managed in a controlled way. However, single-stage systems have limitations. Drainage only affects water that is actually captured. Wind-driven rain carried past the blades with the airflow has no secondary opportunity for removal.

Multi-stage drainable louvres provide additional layers of rain defence. Instead of relying on a single impact point, the airflow is forced to change direction multiple times. As the air slows and turns, water separates from the airstream before it can move deeper into the louvre stages.

The separated water is then captured internally and drained away in a controlled manner. This system improves overall rain-defence by actively managing water throughout the louvre.

Key Takeaways -

1. Single-stage louvres primarily deflect water.
2. Multi-stage louvres actively separate water from the airflow.
3. Drainable louvres manage captured water effectively.

The highest-performing louvre systems combine all three strategies, reducing the risk of water ingress across the board.