Based in Mumbai, bT Square Peg is involved in creating sustainable low-cost designs in architecture and interiors. Founder & Principal architect Vistasp Mehta who has a special interest in energy & water conservation considers glass curtain walls and façades inappropriate for India’s tropical climate and tells us why.
We see them everywhere these days, from Gurgaon to Goregaon – soaring up to the sky, reflecting the clouds and their surroundings in glossy mosaic. They are symbols of modernity – of having arrived. But beauty is skin deep and the glass façades of these buildings are mere skins.
Our country has a huge power shortfall and the situation is not going to change in a hurry. Any enhancement in generation capacity is instantly gobbled up by vastly increased consumption. Meanwhile, massive quantities of fossil fuel continue to be burned, thereby exacerbating climate change and making people install more air-conditioning – which needs more electricity. It is a vicious cycle and this fixation with the “international look” that glass curtain walls are supposed to supply only adds to our already considerable problems. A friend who had left India in the late 1980s and lived abroad for many years, on seeing the steel and glass buildings in Mumbai’s Bandra-Kurla Complex, felt proud that India was “moving up the value chain” and “emerging from the dark ages”. “Finally”, he enthused, “it looks like any city back home and it’s got that international look!” My friend’s way of seeing things is not unusual. There is a strong tendency in India these days to design buildings with glass curtain walls. These are viewed as making a break from our country’s socialist past when buildings looked like piles of matchboxes, when electricity was in short supply and when air-conditioners were a rarity. Well, here’s a news flash – many glass buildings still look like glamorous piles of matchboxes, we’re still perennially short of power and we cannot – as a nation – afford to run so much air-conditioning.
Similarly, on a recent trip to Aurangabad, I was shown around a newly constructed office building. It stood at a busy junction and it had a glass façade wrapped prominently around its corner. I asked the owner why so and he shook his head sadly. I learnt, to my surprise, that he had been against the idea but a famous architectural firm from Mumbai, which had designed the building, overruled him, arguing that he would not be able to sell a single lease if the building didn’t have the requisite “show”. In a city where the power often fails, was there any justification for glass curtain walls beyond the questionable visual aspect?
Glass-skinned buildings became popular in cold climates, where most of the energy is used for heating not cooling. In India and the rest of the tropics, it is the opposite and yet, our architects and builders persist in enveloping their constructions in glass. Once, on a client request to evaluate some office premises in Mumbai for leasing, I visited one office space that had glass curtain walls on the North, East and South faces. The East wall faced the road and essentially, bore the brunt of strong sunlight. The West was mercifully, protected by the staircase and lift blocks. Despite it being a very pleasant, overcast, January morning, the empty office was sweltering hot inside. There were a total of just six openable windows in the entire 250sqm and swinging them outwards as far as they would go did absolutely nothing to alleviate the stifling conditions. For the record, the client and I both agreed to look elsewhere.
Consequences of Glass
• A glass façade causes the building to behave like a greenhouse as it easily allows short wavelength light to pass through. Once reflected off objects in the room, it gets trapped as heat and interior temperatures rise.
• This trapped heat needs to be expelled but buildings with glass façades are mostly devoid of significant natural ventilation. To cool the space air-conditioning has to be of a considerably higher capacity, given the greenhouse-like situation.
• Glass buildings strongly reflect sunlight to their surroundings and in addition, air-conditioners take all that excess interior heat and throw it out into the atmosphere. These factors add to the urban heat island effect causing the temperatures in the immediate vicinity of such buildings to rise by as much as 17°C, as per a reported study by the National Environmental Engineering Institute (NEERI).
• Since natural ventilation is practically non-existent and the air inside is not changed often enough, occupants tend to suffer from “sick building syndrome”.
• In India, the light streaming in through windows translates as glare that can lead to loss in productivity and in some instances early cataract.
Glass manufacturers proclaim that the newly developed and scientifically proven products reduce heat build-up by as much as 30-40% or even more over conventional glass. But, wouldn’t avoiding a glass wall in the first place reduce the heat-gain by a greater margin?
Lighting load saved or HVAC load added
A specious argument put forth for using glass walls is that it reduces the usage of electricity for lighting. Consider a 10m² space. In any standard building, the air-conditioning load would be approximately 3,500W (or 2,500kW if you’re using a highly efficient HVAC system). Lighting this space needs no more than 100W of standard fluorescent lighting and even less if you’re using LEDs. The maximum possible saving that can be achieved by eliminating artificial lighting is, therefore, merely 100W. On the other hand, because it is a glass building, the additional HVAC energy requirements will significantly be higher than they would for a conventional structure. Even if expensive low-emissivity glass is used, I’m afraid no amount of marketing spin can get past simple mathematics.
There are other factors too, which have nothing to do with energy usage. Birds, get disoriented by glass buildings especially during migrations and often die or sustain critical injuries when they slam against the huge transparent panes. Manufacturers are developing special types of glass that are more visible to birds but these will naturally cost more.
Also, highly reflective panes can be a major nuisance for those who live, work or even drive in the vicinity of a glass building. The reflections cause uncomfortable glare and heat build-up for others in the neighbourhood. And finally a glass building is more unsafe during a fire than an equally outfitted conventional building as there is no scope for ventilation. People trapped in glass buildings during a fire, all to often die of asphyxiation – unless the glass shatters, thereby endangering the occupants as well as the rescuers.
With such a long lot of negatives, it is distressing that so many architect continue to prefer designing buildings with glass facades.