Glass has become very fashionable now but how much sense does it really make?
Glass seems to be the material a la mode now. We see it in facades and floors, as furniture and fixtures, as building material and as décor. We even retrofit ancient buildings with glass. But is glass really the right choice for our tropical city?
Glass traps solar heat and warms up the building’s interiors, which is why this gleaming material is favoured in cold places. In recent times though, sunny urban India has taken to a widespread and indiscriminate use of glass. This has raised energy challenges because of the acquired heat gain within the building, while the glassy building itself becomes a virtual heat island in the area. On the other hand, if judiciously used, glass does have its uses.
It looks good, gives great views, lets in plenty of sunlight, and seems handy to fit. So, when we opt for glass, we need to make an extremely well-informed and calculated choice that considers the building’s location, orientation and user needs, rather than just style.
Though there are some glass varieties that give better heat insulation than others, glass usually traps more heat than masonry or brick. “Mindless use of glass is like creating a problem that you have to struggle to solve,” says architect Pradeep Verma.
He suggests that in Indian cities, in the context of sunlight received, we must minimise the use of glass on western and eastern building faces, which get the brunt of the heat.
“We could increase the area of glass used on a building’s northern face, and to a smaller degree on the south,” he says. Architect Ponni Concessao offers another solution: “The outer envelope and perimeter walls of the building should have more masonry, with punched glazed windows. The walls overlooking internal courtyards and partition walls can be 100 per cent glazed glass.”
What to use
Opt for high performance glasses that have a special coating to reduce heat transmission, such as double- and triple-glazed glass — layers of glass with insulating gaps in between.
“These reduce the heat intake into the building by one half or a quarter, compared to plain float glass. But they are also four-ten times more expensive,” says Verma. Concessao says that glass is more expensive than brick per sq. ft, but installation is faster and cleaner.
“There are savings in project cost and time frame.” But in terms of embedded energy, the manufacture and use of any kind of glass leaves a vastly greater carbon footprint than brick.
A wide range of decorative glass is available in the market. The opaque ‘planileque’ glass with colour coating on one side, for instance.
There are also other varities like the laminated bullet proof glass used in high-security homes, glass bricks and tiles, glasses with patterns and sandwiched design, and more.
Some expensive glasses can turn from clear to opaque at the flick of a switch, some come impregnated with LED lights that can be turned on to give a glow or even change colours. There is also thick load-bearing glass that one can walk on if used as flooring.
Is glass safe?
Some types of glass are as tough and safe as wooden doors or windows. “Safety films are available; we could take two 6mm toughened or heat-strengthened glass sheets and put PVB film between them, but people still have a fear perception,” says Verma.
“For exteriors, laminated glass is better as it doesn’t break into sharp pieces on impact and can be replaced safely,” says Siddarth Money, architect, KSM Architecture. When using larger glass panels, the thickness can be increased from the conventional 4-6 mm to 8, 10 or 12 mm to avoid shattering. For the same reason, top quality hardware must be used.
As for fire safety, “enough opening panes must be incorporated into the glass façade to allow ventilation and evacuation,” says Money, adding that in rooms that have files or other documents, ‘pyrostop’ or fire-resistant glass could be used.”