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| Style with shade |
| Himanshu Burte / Jul 25, 2010, 00:42 IST |
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In a hot country like India, even roofs and walls need shelter from the sun. Fortunately, this can be elegant as well as practical
Sitting in the shade of a tree is one of life’s simple comforts. As it happens, a well-shaded building, too, is more comfortable to live in than one that is fully exposed. Many traditional and modern buildings have developed unique aesthetic qualities by paying heed to this fact. It is a pity that most architects today are uncomfortable designing chhajjas (weathershades) even over windows.
It might seem strange to talk about shading buildings. After all, isn’t the roof itself meant to shade us? True, but as anyone who lives directly under an RCC roof knows, buildings get hot. Real hot. Once hot, they radiate the heat indoors. When an indoor space is hot, we turn to electricity — fans, evaporative coolers, airconditioners — to make it comfortable. Installing the right permanent or adjustable shading for buildings can help us avoid or reduce the use of such devices, conserve energy and reduce greenhouse gas emissions. In the process, we can also save a significant amount of money over the course of a building’s lifespan.
Shading the roof
Almost 70 per cent of the heat that comes indoors enters through the roof. Traditionally, flat roofs in the hot parts of the country, especially in low-rainfall areas of north India, are packed with mud (an insulator) to stop heat passing through. Insulating roofs is a good idea, of course, but preventing the sun from hitting the roof, especially an RCC roof, is even more basic. It is also much easier to do today, because of new material and design options.
Roofs can be shaded fully or partially. A light roof in any material (thatch, tile, or sheets of metal or PVC) can be erected on simple steel or other supports over the main roof of a building. In high-rainfall areas, these are often added once the RCC roof starts leaking — but they work equally well to keep the heat out. However, building laws usually calculate a fully shaded terrace as part of the built-up area of a building, whenever the additional shelter may have been built. So it is important to discuss this option with local building-permissions officials first.
Partial shading can actually be comparable in effect and less complicated legally. Here too the choices are many, ranging from shade nets to fixed pergolas. Shade nets are an interesting option that is not often used by architects. Different nets block different percentages of sun. A shade net that cuts off up to 70 per cent of the sun effectively reduces heat gain in the building by about half.
Typically used in floriculture, and made of synthetic materials, shade nets are inexpensive to install (but check their durability). Because they are light, they require a very economical supporting structure. Their lightness also means that the screen can be made in unusual shapes.
Pergolas are a more standard option. A pergola is basically a trellis-like screen placed horizontally like a roof over any space. It may be built in any material or combination — wood, metal, concrete, PVC pipe.
Synergy, comfort and style
There is no doubt that solar shading makes interior spaces cooler. Like most other principles of climate-sensitive design, however, shading devices are most effective when used with related strategies. A shaded wall or roof that also has insulating hollows within it is likely to heat up much more slowly than one without the hollows, for instance.
Shading can also lead to a cooler appearance. Screens and ‘second skins’ are important elements of the creative architect’s toolkit. Thus, solar shading can help us explore an innovative aesthetic which is relevant to the specific place and climate in which we live.
| SHADING EXTERNAL WALLS
Different shading methods for walls must be used against the midday sun and the morning or evening sun. For places in India at latitudes north of Ahmedabad or Kolkata, the midday sun shines only on south-facing walls. South of Ahmedabad, the summer sun also shines on north-facing walls.
The high midday sun can be cut off easily by relatively small horizontal projections like chhajjas, cornices and even copings over parapet walls. Traditional architecture often uses these solutions. The detailed decoration and carving on facades of traditional buildings casts a web of micro-shadows that reduces heat gain through the walls. Chhajjas in continuous bands around a building at regular vertical intervals also can keep the wall in shadow, and therefore, cool.
The sun is low in the sky in the morning, late afternoon and evenings, and its rays hit building walls obliquely. Hence, horizontal projections like chhajjas don’t work very well for east- and west-facing walls. Here, vertical screens, or ‘fins’, are the most effective way of blocking out the sun. Jali walls in brick, wood or other materials can function as screens, when built a short distance from the external walls. Screens could also be trellises in wood, metal or rope, covered with creepers that may also bear flowers, fruit or vegetables.
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