What is a brise soleil?
A brise soleil — French for “sun breaker” — is a fixed or adjustable external shading array that intercepts solar radiation before it reaches the glass. In practice the terms overlap:
- Brise soleil is the architectural term, usually implying an array that is part of the elevation's composition rather than a discreet add-on.
- Louvre façade (spelled louver in American usage — same thing) is the technical term for the assembly: blades, carriers and substructure.
- Solar shading describes the function, which may also be achieved by glass coatings, internal blinds or external fabric.
- Screening describes the same assembly used to conceal rather than to shade — rooftop plant, car park decks, service yards.
One distinction worth keeping clear: a louvre array is made of spaced linear blades, which gives directional control — it can block sun from one angle while staying open to view from another. A perforated screen is a flat sheet with openings, which behaves the same way in every direction. The two solve different problems, and the choice between them should be made on solar geometry rather than appearance.
- Blade depth
- 100 – 400 mm
- Blade spacing, centres
- 150 – 500 mm
- Free area
- 40 – 70%
- System weight
- 8 – 18 kg/m²
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Blind inside the glass The radiation is already inside. The blind sends only part of it back out; the rest warms the room and becomes cooling load.
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Blades outside the glass The radiation is intercepted before it reaches the glass, so the heat is removed before it becomes a cooling load.
Orientation decides the blade
This is the part that gets reversed most often, and it is expensive to correct once the elevation is built.
The sun's position relative to a façade changes with orientation. Horizontal blades control how high the sun can be before it reaches the glass; vertical fins control how far round it can come. The same louvre performs differently on each elevation.
| Elevation | Sun behaviour | Blade orientation |
|---|---|---|
| South | High in the sky through the middle of the day, when radiation is strongest | Horizontal. A horizontal blade cuts high-angle sun efficiently and leaves the low view uninterrupted. |
| East / West | Low and nearly perpendicular to the façade at sunrise and sunset — the hardest condition to shade | Vertical, angled or closely spaced. Horizontal blades are close to useless here; low sun passes straight under them. Fins set square to the façade let sun from straight ahead pass between them, which is why these elevations are where adjustable blades earn their cost. |
| North (northern hemisphere) | Little direct sun; mostly diffuse light | Usually none. Shading a north elevation removes useful daylight and adds cost for very little gain. |
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South: horizontal blades Cut the high midday sun efficiently and leave the low view uninterrupted.
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East and west: vertical fins Low sun from the side is caught by the fins. Sun from straight ahead passes between fins set square to the façade — where adjustable blades earn their cost.
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North: usually none Little direct sun. Shading here removes useful daylight and adds cost for very little gain.
Northern hemisphere. Angles illustrative — the sun path for the actual site decides.
Raked or diagonal blades exist for elevations that do not face a cardinal direction, or where the array is doing architectural work as well as solar work. The angle is set against the actual sun path for the site rather than chosen visually.
Two delivered projects show the range. At the pharmaceutical plant in Al-Diwaniyah, southern Iraq, the envelope uses vertical louvres. At Sobhan Biotech in Pardis Technology Park, Tehran, the array is diagonal — there the blades brace the façade against seismic movement as well as moderating solar gain, and a full-scale mock-up measured the interior daylight before the field was committed.
Blade geometry: depth, spacing and cut-off
Three numbers define the array, and they work as a ratio rather than individually.
- Blade depth: 100 – 400 mm. Deeper blades shade more but weigh more, attract more wind load and obstruct more view.
- Blade spacing: 150 – 500 mm centres. Closer spacing shades more and darkens more.
- Free area: 40 – 70%. The proportion of the elevation that remains open. This is the number to hold on to, because it governs both how much light gets through and — where the louvre is also a ventilation opening — how much air does.
The concept that ties them together is the cut-off angle: the sun angle (strictly, the profile angle) above which a given depth-to-spacing ratio fully shades the glass behind. A deep blade at wide centres and a shallow blade at close centres can produce the same cut-off angle with very different appearance, weight and cost.
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The cut-off angle Sun steeper than this profile angle cannot pass between two blades to the glass. For flat blades, its tangent is the spacing divided by the depth.
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Same angle, different array A deep blade at wide centres and a shallow blade at close centres cut off at the same angle — with very different appearance, weight and cost.
Flat horizontal blades, in section. Both arrays in the second drawing have the same spacing-to-depth ratio.
The practical consequence: design the array to the cut-off angle you need for the orientation and the latitude, then choose the depth-and-spacing combination that delivers it at the appearance and weight you want. Most projects that end up dark inside chose spacing visually first and discovered the cut-off angle afterwards.
Shading should be modelled against the sun path for the actual site. Latitude changes the answer significantly — a scheme that works in Yerevan at roughly 40° north will over-shade in Dubai at roughly 25°, where the sun sits much higher.
Aerofoil or rectangular?
Both are available on this system, and the choice is not only visual.
Rectangular blades are simpler to extrude, cheaper, and read as a crisp line. They present a flat face to the wind, which means higher wind load per blade and more turbulence behind the array.
Aerofoil blades are shaped so air passes more cleanly. That matters in three situations:
- Exposed elevations, where wind load on a deep rectangular blade drives the substructure cost up.
- Where noise matters. Deep blades can whistle — air separating from a sharp edge at particular wind speeds generates tone. An aerofoil section is far less prone to it. On a hospital, a hotel or a residential building this is worth the cost difference on its own.
- Where the blade is seen end-on. An aerofoil reads as a thinner, more resolved profile from an oblique view.
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Rectangular Simple and cheap, and reads as a crisp line. The flat face takes more wind load, and air separating from the sharp edges can whistle.
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Aerofoil Shaped so air passes cleanly: less wind load on exposed elevations, far less prone to whistling, and a thinner profile end-on.
Sections; streamlines schematic.
Wind load and acoustics are both checked at design stage where the elevation is exposed, rather than discovered in the first winter.
Fixed or adjustable
Adjustable blades perform better and cost more, and introduce motors, controls and a maintenance regime.
That sentence contains the whole decision, but it is worth unpacking, because adjustable arrays are specified on projects that did not need them and omitted from projects that did.
Fixed blades are sized for a worst-case sun angle. They are maintenance-free, have no failure mode beyond the fixings, and last as long as the finish. The trade is that they shade at times you would rather they did not — winter mornings, overcast afternoons — because they cannot know the difference.
Adjustable blades, manual or motorised, track the sun and can open fully when there is nothing to shade. The real gains are in mixed climates with a meaningful heating season, where winter solar gain is useful and summer gain is not.
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Fixed Sized for a worst-case sun angle. Maintenance-free and lasts as long as the finish — but shades at times you would rather it did not.
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Adjustable Closes against direct sun and opens fully (dashed) when there is nothing to shade — with motors, controls and a maintenance regime.
What adjustable brings with it:
- Motors, controls and a BMS interface, with commissioning and a control strategy that someone has to own.
- A maintenance regime. Motors and linkages are consumable items on a twenty-year façade, and access for replacement has to exist from day one.
- A failure mode. A fixed louvre that fails is still a louvre. A motorised array stuck in the closed position is a dark building, and stuck open is an unshaded one.
When adjustable earns its cost: a significant heating season alongside the cooling one; a façade where the shading requirement changes sharply through the day, typically east or west; or where the movement itself is part of the architecture. On a single-season cooling climate with a south elevation, fixed blades usually win on whole-life cost.
Span, deflection and why appearance governs
Maximum span between supports: 1,500 – 3,000 mm, profile dependent.
Blade deflection is visible long before it is structural. This is the point most often missed: a blade can be entirely safe and still look wrong.
A row of parallel blades is one of the most unforgiving arrangements in architecture. The eye reads the lines against each other, so a few millimetres of sag in the middle of a span is obvious from across the street — it registers as a wavy line in what should be a straight rhythm. The structural check passes; the elevation still looks defective.
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Supports close together The lines stay straight and read as one rhythm. The support positions become part of the elevation.
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Supports far apart Structurally fine, visibly wrong: a small sag in the middle of each span reads as a wavy line against its neighbours.
Elevation. Sag exaggerated.
So support spacing is set by appearance, which usually means a tighter grid than strength alone would require. Three consequences worth designing for early:
- Support positions become part of the elevation. They interrupt the blade line, so they should be regular and deliberate rather than wherever the structure allows.
- The carrier system is the real engineering. Blades are simple extrusions; the brackets, back-span and connection to the primary structure are where the cost and the tolerance live.
- Longer spans need deeper or stiffer profiles, which changes the shading geometry. Span and blade depth cannot be decided independently.
Weight, substructure and thermal bridging
System weight: 8 – 18 kg/m².
That is light for a façade element, but it arrives at the primary structure through a small number of brackets, so the point loads are not trivial — particularly with wind. Three things to resolve:
- Back-span structure. Where the louvre spans between floors or across a soffit, the supporting element is designed with it, not after it.
- Thermal bridging. Every bracket that penetrates the insulation line is a thermal bridge. On a shading array with a regular bracket grid these add up, and the effect on the wall's overall U-value should be calculated rather than assumed negligible. Isolators and thermally broken brackets exist for this.
- Movement. Aluminium expands considerably more than steel or concrete. A long horizontal blade run needs its expansion accounted for at the fixings, or it will bow between supports in summer.
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Plain bracket Every bracket that crosses the insulation is a thermal bridge. On a regular bracket grid they add up.
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With a thermal isolator Isolators and thermally broken brackets cut the path. The effect on the wall’s U-value is calculated, not assumed negligible.
Section, simplified.
The other three jobs louvres do
Shading is the headline, but on most projects the same system is doing at least one of these:
Rooftop plant screening. Concealing chillers, AHUs and condensers while letting them breathe. Free area is the governing number here: the plant has an air requirement, and a screen that looks right but restricts intake will cause the equipment to underperform or trip. Coordinate free area with the mechanical engineer before the blade spacing is fixed.
Car park ventilation façades. Naturally ventilated car parks have a minimum free-area requirement from the local code, and the louvre has to deliver it while also meeting the appearance and, often, the security brief. Codes usually count the louvre's free area — 40 – 70% on this system — rather than the size of the opening, so the figure is checked against the code rather than assumed.
Screening and privacy. Balconies, terraces, service yards, plant rooms. Here the directional property of blades earns its keep — an array can block the view in from the street while leaving the view out open, and it does so by blade angle. A perforated sheet's privacy depends on which side is brighter, and it inverts when lit from behind at night.
- View out stays open A level line of sight passes between the blades.
- View in from below is blocked A line rising from the street meets a blade — the angle does the work.
- A perforated sheet cannot do this Its privacy depends on which side is brighter, and it inverts when lit from behind at night.
Section. Whether a line of sight is blocked depends on blade depth, spacing and angle together.
Finish and service life
Three options on this system, and the choice is about environment more than colour.
Powder coat to EN 12206. The widest colour range and the lowest cost. Modern architectural powder coatings perform well, but in strong UV and high heat — most of the Gulf and central Iran — the colour and gloss retention depend heavily on the coating class specified. Ask for the class, not just the RAL number.
Anodising, 20 – 25 µm. An integral oxide layer rather than an applied film, so it cannot peel or chip, and it wears rather than fails. The 20 – 25 µm thickness is the architectural range for external use. Colour options are narrower and batch-to-batch consistency needs managing across a large elevation, but under strong UV anodising generally holds its appearance longer than a coating. On the coast, either finish needs the right class and regular washing.
Wood-effect finishes give timber appearance with aluminium's service life. Worth checking the UV warranty specifically, since the grain is a pattern transferred into or printed over a base coat, and it weathers differently from a solid colour.
On cleaning: a louvre array collects dust on every upward-facing surface, and in dusty climates that changes both appearance and — on plant screens — free area. Cleaning access should be resolved at design stage. It is the same argument as glass replacement on a curved roof: retrofitting access is expensive and it is nearly always someone else's budget by then.
What to decide, and when
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Concept
What the louvre is for — shading, screening, ventilation, appearance, or several at once. The orientation of each elevation it appears on. If it is shading, the cooling strategy it is meant to support.
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Developed design
Sun path modelling per elevation, target cut-off angle, depth and spacing, free area agreed with the mechanical engineer where ventilation or plant is involved, and the fixed-versus-adjustable decision.
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Technical design
Blade profile, span and support grid, bracket and thermal isolation detail, movement strategy, finish specification and class, and cleaning access.
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Before tender
A defined blade profile and support grid. A louvre elevation tendered on appearance alone gets priced on the cheapest profile that looks similar, which is usually not the one that meets the deflection or wind requirement.
