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We can’t seem to have enough of glass. It has become the symbol of modernity. And with good reason too. It is a versatile industrial material, lets in light through windows, lets us see through (or not, depending on whether it is translucent) and makes for shiny, clean surfaces and building forms.

Image: StockXpert

But does it actually work that way? Is the glass curtain-wall (a continuous curtain of framed or connected glass sheets fixed to the structural frame) more about style than about saving money or the environment?

Most importantly, what portion of buildings—even in “developed" countries with cold climates, such as the US—actually use glass in a way that maximizes benefits and minimizes costs?

“A very, very small portion," says Prasad Vaidya, an architect and energy analyst with The Weidt Group in Berkeley, California, who advises building professionals on energy matters.

As a broad rule of thumb, Vaidya suggests that the proportion of glass areas in windows must be kept between 12 to 25% of the total floor area in the US, so that interior spaces do not get overheated.

If that is ideal in the much-colder US, what’s with all the full glass towers in scorching Gurgaon (or Hyderabad)?

Glass and climate

Climate is important when thinking of glass in buildings. Glass is valuable in buildings fundamentally for its transparency, which lets in natural light. Hence its regular use in windowpanes.

But glass also lets in heat along with the light. And it allows only light to reflect back, trapping the heat inside.

Fixed glazing (or fixed panels of glass, as in picture windows in homes, or the large curtain walls on commercial buildings) on building exteriors thus helps create a greenhouse effect. When the curtain wall faces the west, it lets in the hottest sunlight of the day and turns the interior space into an oven. Of course, the simplest solution is to open the window. But windows clutter the smooth look of the curtain wall, and for that reason are not enthusiastically provided by architects.

In the heat of India, this means that the air conditioning works harder and costs more in terms of installation and electricity bills (while also emitting ozone-depleting chemicals such as chlorofluorocarbons). Of course, the more conspicuous the consumption, the more status it buys. A glass tower broadcasts the ability of the owner-occupier to pay for all this.

Reflection of modernity

But it is not only about power. With the curtain glazing being thin, it allows developers the extra floor space that omitting the external wall creates. Also, it is quicker to assemble than the age-old plastered brick wall, though aluminium composite panels (ACPs) offer competition to curtain glazing on this front.

Some architects may also be in thrall of glass for visual (and historical) reasons alone. Along with concrete, glass was a wonder material for early 20th century modernist European architects. Design leaders such as Le Corbusier (who later designed Chandigarh) and Mies van der Rohe were trying to create a new language for European architecture that expressed the high level of industrialization Western societies had achieved. Out with the heavy, overwrought architecture of stone and brick, they said. And in with white walls, unornamented “forms" (that is, three-dimensional shapes) and industrial materials such as concrete, steel and glass.

That language was disseminated all over the world, including India. And glass went on to tighten its grip on the imagination of architects as industry developed products that mitigated its heat absorption and insulation problems. A building wrapped in glass is easier to make attractive to the popular imagination than one in which different materials have to be balanced visually.

Intelligent use

Like fire, glass works excellently if used well. The Gurgaon headquarters of Apollo Tyres, designed by Morphogenesis Architecture Studio, has “finger-like" indoor spaces alternating with enclosed open spaces, which let reflected daylight into the interiors. The reflected light is relatively glare-free and much cooler. The floor-to-ceiling glass is designed to let this light into the workspace and reduce electricity consumption to a very large degree.

Building plans can also be sensitively organized so the spaces receiving daylight through windows or curtain glazing are oriented correctly to reduce direct heat gain and let in the maximum amount of daylight.

It is also possible to provide sunscreening devices outside the glazed surface so that the hottest sun is screened off. After all, the path of the sun is fixed—and so is the angle of the building in relation to it.

To glaze or not to glaze

It all boils down to knowing why glass is being used in a building. If you want to show off, or if you are simply infatuated with glass, not only you, but the entire planet, pays a big price. Glass has a very high embodied energy—the energy that goes into making, transporting and fixing it. The embodied energy of framing materials (aluminium, for instance) is also high. Most of this energy comes from non-renewable sources.

Glass is also an expensive material, and gets more so when you choose to use double or triple glazing products, and those with various reflective coatings. The costs only mount when you consider maintenance.

But used in the right doses, and in the correct place, glass does have the potential to be the bright choice. Of course, that requires commitment, knowledge and time on the design board for all those concerned with building. Do we have enough of all this to use glass with intelligence and responsibility?

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