The use of glass in buildings is here to stay. In today’s urban setting — where warding off dust, smoke and noise from the outdoors has become a necessity — glass windows and doors connect us to our surroundings without exposing us to these pollutants. In fact, glass skylights are an excellent feature to get a glimpse of the night sky from the comfort of your home, and also help light up spaces that do not have access to exterior walls.
How it evolved
Glass was been found as early as 7000 B.C. in the Neolithic period, mainly as coloured glaze on stone and pottery. Its use in buildings was first tried by the Romans, and technological advances in the 1600s lead to the manufacturing of glass for doors and windows. London’ Crystal Palace (built in 1851) is one of the earliest examples of sheet glass being used in a building on a large scale: it has 3,00,000 glass panes.
The advent of metal frame structures paved the way for glass walls and glass façades, features commonly in skyscrapers today. However, glass is a material that will let in heat easily and trap it too. In a place like Chennai, where we need to minimise heat ingress into interior spaces, this characteristic of glass is counter-productive. Having said that, advanced technological research has resulted in multiples types of glazing: low-emissivity (low-E) glass, insulating glass and solar control glass.
Considering the prevalence of the material, it is imperative to understand its properties and be aware of available options. What you need to look out for is the material’s Solar Heat Gain Coefficient (SHGC), which reflects the amount of direct heat that is let in. Lower the value, lower the direct heat gain. Although solar control glass is more expensive than clear glass, sensible architecture with adequate shading of glass is a cost-effective alternative to prevent direct heat gain.
Heat control
Another factor to look for while selecting glass is its U-Value — which reflects its insulating property. The lower the U-value, better the insulation. Having said that, the U-value of glass (even double glass) is much higher than the U-value of any other wall material as the former is a poor insulator. Considering this, it would be wise to restrict the amount of glass used in buildings.
While evaluating the material’s heat control properties, ensure you don’t compromise on its light transmittance. Look out for its Visible Light Transmittance (VLT); higher the value, better the light transmittance as we need the daylight to come in, not heat.
A sensible and well-thought out selection of glass for our buildings will not only keep us comfortable indoors, but also benefit the environment by reducing the need for air-conditioning.
The author is the founder of Green Evolution, a sustainable architecture firm