Solar Shading and Brise-Soleil
Shading is not there to cast shade: it is there to cast shade in summer and get out of the way in winter. The whole design lies in that difference, and the difference is not settled by taste: it is settled by solar geometry, which behaves so differently to the south and to the west that it demands two different devices.
Overview
TAV. 00Solar shading is the facade element with the highest ratio of effect achieved to material used, and also the one designed most casually. The reason is that it looks like a question of form when it is a question of angles: the summer sun at midday is very high and is stopped by a modest horizontal projection, while the late-afternoon sun arrives almost horizontally and passes under any overhang, however deep. Almost everything follows from that elementary fact: horizontal louvres work well to the south and badly to the west, vertical or adjustable ones are needed precisely where horizontal ones fail, and shading designed without looking at orientation is simply expensive ornament. The second theme, equally decisive and equally neglected, is that shading is a structure hung outside the envelope: it has wind loads of its own, it must be anchored through the insulation and the weather barrier, and it will stay exposed for decades to weather and thermal movement. The typical failure is not optical, it is constructional: water penetration at the anchors, thermal bridges, wind noise, corrosion between dissimilar materials.
The site score
TAV. HThe detail of the craftthe same overhang, two seasons
Solar analysis: orientation decides the type
For each facade the sun's path is reconstructed across the seasons and the hours that matter, the periods when radiation must be blocked and those when it should be let in are identified, and from that the device is chosen: overhangs and horizontal louvres, vertical elements, adjustable systems or variable-transmission glass.
«To the south an overhang stops the sun and no motor is needed. To the west the sun comes straight at your eyes: there you either turn the louvres or you have done nothing.»site notebook — editorial synthesis
click a beat · arrow keys ← → walk the site · dashed pauses are the chemistry at work
The rule that settles everything
To the south an overhang suffices, to the west nothing fixed does
The sun does not behave the same way on every elevation, and that is the technical reason why a well-shaded building has different devices on different sides, even at the cost of giving up a unified image. To the south the summer midday sun is very high and the winter one very low: the same horizontal projection does two opposite jobs in the two seasons, stopping the first and letting the second through, with no mechanism and no energy use. To east and west the sun arrives low on the horizon in both seasons, so it passes beneath any overhang: there the only geometry that intercepts the ray is vertical, or adjustable. And since the afternoon is also when the building has already accumulated heat, west is the elevation where ineffective shading costs the most.
A qualitative diagram of solar geometry; the actual angles depend on latitude and must be taken from the site's sun path diagrams, but the logic of the two behaviours holds at any European latitude.
Why outside, not inside
An internal blind always arrives too late
The difference between shading outside and shading inside is not one of degree but of principle, and it becomes clear by asking where the energy ends up. An external louvre intercepts the radiation before the glass: it heats up, but it is outside, and the heat it has absorbed is carried away by the air moving around it. An internal blind intercepts the same radiation after it has passed through the glass: by then the energy is already in the room, and the blind, heating up, gives it back to the space, becoming itself a heat emitter placed in front of the window. Glass, moreover, is far more transparent to incoming solar radiation than to the infrared re-emitted inside, so it tends to trap it. Hence the practical hierarchy: shade outside first, then choose the glass, and only at the end add blinds, which are there for glare and privacy, not for heat.
A qualitative diagram of the energy balance; the size of the advantage depends on the glass type, the colour of the shading and the ventilation of the gap, but the direction of the difference never changes.
How it ages (and what betrays it)
TAV. PQuestions from the site
TAV. QFixed or movable brise-soleil: when is each worthwhile?
The practical rule comes from orientation, not from budget. To the south the sun changes height greatly between summer and winter, so a fixed element can be sized to stop one and let the other through: movement adds little and brings motors, sensors, maintenance and one more way to fail. To east and west the sun is low in every season and fixed geometry cannot distinguish between the ray to be stopped and the one that might be useful: there, adjustability is the only way to have shade when needed and a view when not. There are two further cases where movement is worthwhile regardless of orientation: when the building needs significant winter solar gain and a fixed screen would cut too much of it, and when glare control is part of how the space works, as in offices or classrooms with screens. In every other case fixed is more robust, and robustness on a facade is worth a great deal.
Is a good internal blind not enough?
For glare yes, for heat no, and the reason is physical rather than a matter of performance. Solar radiation that has passed through the glass is already in: the blind intercepting it converts it into heat inside the room, and becomes itself a hot surface in front of the window. The glass makes matters worse, because it readily admits solar radiation and far more readily retains the infrared re-emitted inside: it is the same mechanism that makes a car parked in the sun hot. External shading, by contrast, heats up somewhere the heat can leave, that is, in open air, and for that reason the difference in effectiveness between the two is not a percentage but a factor. This does not make blinds useless: they are the right tool for glare, privacy and blackout, and many buildings need both. It only means they should not be used to solve a thermal problem, because they come after the glass, and by then it is late.
Does timber hold up outdoors? And how much maintenance does it need?
It does, but the useful question is not whether it lasts: it is whether it stays straight. On shading, timber's main problem is not biological decay, which is solved with the right species or a stabilising treatment, it is dimensional stability. A long, slender louvre exposed to sun on one face and shade on the other has a different moisture content on each side, and tends to bow or twist. On an isolated element nobody would notice; in a regular series a deviation of a few degrees is read by the eye at once. Three practical implications follow. First, choose stabilised timbers, thermally treated or chemically modified, which greatly reduce hygroscopic movement. Second, design fixings that allow a little movement rather than resisting it, because timber that is restrained does not stop moving, it splits. Third, and this is what generates most disputes, appearance: external timber changes colour, and unevenly, because it depends on exposure. Say so to the client beforehand, and decide whether that greying will be accepted as a patina or resisted, because in the second case you are accepting periodic maintenance forever.
Can shading also generate energy?
Yes, and the combination makes more sense than it might seem, because the two objectives coincide in space: the surface receiving the most sun is exactly the one you want to shade. A photovoltaic brise-soleil uses the louvre as a support for the modules, and has an advantage roof installations do not, namely the ability to be tilted and oriented precisely, and even to rotate tracking the sun in movable systems. There are, however, three conditions to face at the outset, or the system disappoints. The first is mutual shading: louvres set too close shade one another, and on a photovoltaic module partial shade penalises output far more than the geometry suggests. The second is temperature: a hot module produces less, so the louvre must be ventilated on both faces, which means spacing it off the facade rather than resting it against it. The third is the most neglected and concerns time: modules have a service life and an evolving technology, cables and connections fail, so replaceability of the individual element without dismantling the facade must be designed in. Active shading is not a system placed on a building: it is a part of the building that must be maintained like a system.