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

> Aluminium louvres are angled blades, usually extruded 6063 alloy, set in a frame to admit air or light while screening views, sun or rain. The core choice is between screening louvres, which look good but let rain through, and rain-defence louvres, tested to EN 13030, which keep water out at the cost of air flow. Specifying one when the opening needs the other is the usual failure.

## 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](/materials/aluminium-extrusion-6063-t6), 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

| Type | Blade profile | Primary job | Water performance | Typical location |
| --- | --- | --- | --- | --- |
| Screening louvre | Flat, Z or simple angled blade | Visual screening, shading, appearance | Limited; some rain passes | Facade screens, parapets, car-park walls |
| Aerofoil louvre | Curved, aerofoil-section blade | Solar shading, architectural feature | Limited | Brise-soleil, shading fins, operable shading |
| Sightproof louvre | Overlapping chevron or V blades | Blocking the view at any angle | Moderate | Plant screens, service yards |
| Rain-defence louvre | Deep blades with drainage hooks and gutters | Ventilation with water kept out | High, measured by test | Plant rooms, AHU intakes, electrical rooms |
| Acoustic louvre | Deep blades with absorptive infill | Ventilation with noise reduction | Varies by design | DG and chiller enclosures |
| Operable louvre | Any of the above on pivots, motorised or manual | Variable ventilation, smoke vent, tracking shade | Depends on blade and seals | Atria, smoke vents, adaptive facades |

## 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](/glossary/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](/services/facade-glazing/rainscreen-ventilated-systems)
apply. Where the brief is screening with a flatter surface, a
[perforated metal facade screen](/materials/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.

## Frequently asked questions

### What is the difference between a screening louvre and a rain-defence louvre?

A screening louvre is designed for appearance, shade and visual screening, with simple blades that let a proportion of wind-driven rain through. A rain-defence louvre uses deeper, profiled blades with drainage channels to catch and shed water, and its performance is measured in a test such as EN 13030. Use screening louvres where some water is acceptable, and rain-defence louvres where the space or equipment behind must stay dry.

### What is free area, and why does it matter?

Free area is the proportion of the louvre face through which air can actually pass. Higher free area means less pressure drop, so fans and natural ventilation work more easily, but more open blades usually let more water through. The mechanical engineer sizes the louvre from the air flow needed; picking a louvre for looks and then finding it too restrictive is a common and expensive rework.

### Are operable louvres worth it?

They are where the same opening has to ventilate in one condition and close in another, such as a smoke-ventilation opening, a plant room that must be sealed in a storm, or a shading system that tracks the sun. They add motors, linkages, controls and maintenance. For a plant screen or a fixed shading element, fixed blades are simpler and have fewer parts to fail.

### Which finish lasts longest on aluminium louvres?

It depends on exposure and colour. Polyester powder coating suits most inland facades; PVDF coatings hold colour and gloss better in strong sun; anodising gives a hard, metallic finish that does not peel but has a narrower colour range. Coastal and industrial sites need the finish class and pretreatment chosen for that exposure. Blade edges and cut ends are where finish failure starts.

### Do louvres need bird mesh?

Usually, on any louvre that opens into a plant room, roof void or ventilation intake. Birds nest behind blades and block air paths. Mesh is fitted on the inner face, and it reduces free area, so the mechanical engineer must size the louvre including the mesh, not before it is added.

### Can louvres replace glazing on a plant floor?

Often, and it is one of their main uses: a louvred screen hides chillers, cooling towers or DG sets while letting them breathe. Whether the equipment's air flow, noise and exhaust recirculation work with that screen is a question for the MEP and acoustic engineers, because a screen that is too closed can cause equipment to re-ingest its own hot air.

## Sources

- [EN 13030](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Ventilation for buildings — terminals — performance testing of louvres subjected to simulated rain
- [EN 12206-1](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Coating of aluminium and aluminium alloys for architectural purposes — thermosetting coating powders
- [IS 875 (Part 3)](https://standards.bis.gov.in/website/published-standards/department-wise) — Design loads for buildings and structures — wind loads

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Source: https://hagerstone.com/materials/aluminium-louvre