Aluminium Louvres — Facade Screens, Plant Screens and Rain-Defence Louvres

What it is

An aluminium louvre is a frame of angled blades that lets air or light through an opening while screening rain, sun or the view. Blades are usually extruded aluminium, most often alloy 6063 in the T6 temper, with a matching extruded frame.

The commercial question is what the opening has to do. A louvre chosen for the elevation and then asked to ventilate a plant room, or keep a switch room dry in monsoon rain, either starves the equipment of air or lets water in. Both are discovered after handover, and both mean replacing louvres that have already been paid for, fixed and finished.

Louvre types and where each is used

Free area versus water penetration

This is the trade-off that decides most louvre specifications. Free area is the share of the face through which air actually passes. The more open the blades, the lower the pressure drop and the easier the fans or natural ventilation work. But open blades admit more wind-driven rain.

Rain-defence louvres solve this with deeper, profiled blades that catch water and drain it, which costs free area and depth. EN 13030 measures this directly: it tests a louvre section under simulated rain and wind, with and without air flowing through it, and reports water rejection alongside pressure drop. Comparing two louvres on free area alone, without their tested water performance at the same air velocity, is not a like-for-like comparison.

The sequence that works:

1. The MEP engineer states the air flow through each opening and how much water is acceptable behind it
2. The louvre is selected from tested data to meet both, including the effect of bird mesh
3. The facade designer fits the elevation around that louvre, not the other way round

Finishes

Louvres are exposed on both faces and at every blade edge, which makes finish selection more demanding than for a flat panel.

• Polyester powder coating to EN 12206-1 suits most facades and offers the widest colour range
• PVDF (fluoropolymer) coating holds colour and gloss longer in strong sun and is often chosen for dark colours
• Anodising gives a hard metallic finish that cannot peel, with a narrower colour range

The trade-offs are set out in anodising vs powder coating. Whatever is chosen, blades should be finished after cutting where possible, because site-cut ends left bare are where corrosion and finish lifting begin.

Fixings, support steel and bird mesh

Louvre screens catch wind across their full face, so the frame, its fixings and any secondary steel are designed by the structural engineer for the wind load on that building under IS 875 (Part 3). Long blade spans flutter and rattle if blade support spacing is set by appearance rather than by calculation.

• Isolate dissimilar metals. Aluminium fixed directly to mild steel or galvanised steel without separation corrodes at the contact.
• Use stainless steel fasteners of the grade the exposure calls for.
• Fit bird mesh on the inner face of any louvre into a plant room, void or intake, and include it in the free-area calculation.
• Detail a drained sill behind rain-defence louvres. Even the best louvre passes some water in extreme weather, and it needs somewhere to go.

Where louvres form part of a larger screen or a ventilated cladding zone, the cavity and drainage principles of rainscreen ventilated systems apply. Where the brief is screening with a flatter surface, a perforated metal facade screen is the usual alternative.

Common mistakes

• A screening louvre on a plant-room intake. Looks right on the elevation, lets monsoon rain onto the equipment.
• Free area quoted without mesh. The bird mesh goes on later and the air flow falls short.
• Louvres sized after the elevation was fixed. The opening is too small for the air flow, and the fix is a bigger hole in a finished facade.
• No drained sill. Water that passes the blades sits on the slab edge or runs into the building.
• Aluminium bolted straight to steel. Galvanic corrosion at every bracket.
• Operable louvres with no maintenance access. Motors and linkages that cannot be reached are not maintained, and seize.

What to ask your contractor or supplier

• Is this louvre a screening or a rain-defence type, and what does the brief need?
• What are the tested free area, pressure drop and water rejection, and to what standard?
• Does the free area quoted include bird mesh?
• What alloy, finish system and pretreatment are proposed for this exposure?
• How are the blades and frame supported, and who designs the secondary steel?
• How is water that passes the louvre drained?

Standards referenced

Water rejection and pressure drop of louvres under simulated rain to EN 13030. Powder coating of architectural aluminium to EN 12206-1. Wind loads on facade elements and their supports to IS 875 (Part 3). Air flow, water performance and wind design for a specific building must be confirmed by the project's MEP, facade and structural engineers.