Jayanthi Venkatachalam, a homemaker in her late 40s, resident of Jeevanbheema Nagar got the roof of her house painted white recently. Her husband, S V Venkatachalam, a scientist at ISRO, heard of painting roofs white as a method to keep buildings cool from a friend and decided to try it. She says, the rising mercury made life unbearable for her family as a fan was just not enough to provide relief.
Jayanthi says they did not go for air-conditioners or air-coolers because of the cost in terms of buying one and also monthly electricity bills incurred in running them. Although it has only been a few days since they painted the roof white, Jayanthi says they are already feeling comfortable. "This change is obvious and our house is much cooler than before, we do not feel the need to go for air-conditioners or coolers with this," says Jayanthi.
Painting roofs white is not a new idea for Ramesh Sivaram, 39, a Director of a food processing company. He painted the roof of his house, on Sarjapur Road almost five years ago. He used good quality exterior water-proof paint for his roof. He now needs to apply a single coat once in two to three years. "My house is at least a few degrees Centigrade cooler than before," says Sivaram.
There are many options for anyone interested in painting their roofs white. One can do a simple whitewash of the roof but it will have to done regularly as the rains might wash away the paint. The albedo levels of such paints might also be lower. Albedo is the scientific term that denotes the reflecting power of a surface.
Newer paints in the market claim to have been specifically designed with high albedo. Lenin Sundararajan, who runs LAKS Technologies, manufactures and distributors of paint called Sun Sheetal. He says it is can reflect up to 86 per cent of sun’s rays. Sun Sheetal can cost between Rs 20 – 25 per square feet including labour.
A Ali, of Karnataka Hardware and Paints in J P Nagar says Kool-n-Seal paint by Birla White used for painting roofs is one of their best selling products. The demand for the paint, says Ali, is so much that they are out of stock and are still waiting for arrival of new stock. "A 25-kg tub of the paint costs Rs 2300 and can cover an area of 30 – 35 square feet," says Ali.
Hiten Chavda, lead architect of Bio-diversity Conservation India Limited (BCIL) says that over 70% of heat in a building enters through the roof and is heated up quickly, especially by infra red and ultra violet rays of the sun. Building materials being good conductors of heat radiate this to the inside and trap it there. While the rest of the earth cools down after the suns sets, our homes are still warm inside. To combat this, Chavda says, roofs can be painted white as the colour reflects a large part of the sun’s rays back in to the atmosphere, thus reducing the heat absorbed by the building.
Temperatures, Chavda says, can differ by as much as 10 degree centigrade between painted and non-painted roofs. To get the best effect, he says, high albedo paint should be used. "High albedo paints are highly reflective and can reduce conductivity of heat considerably. In our buildings, we have found reduced energy consumption for cooling drop by as much as 20%," he says.
White roofs can even help reduce the ‘Heat island effect’ one of the causes for rising temperature in urban areas. Concrete structures and tarred roads not only heat the surroundings, they also trap it. So urban areas become islands of heat. But with white roofs, more heat is reflected back in to the atmosphere, cities can remain cooler.
Naresh Narasimhan, principal architect at Venkatraman Associates, an architectural firm based in Bangalore says it has been long since benefits of painting roofs white have been known. "Not only can they keep homes cooler, if all surfaces in the city are painted white, they will bring down the temperature of the area considerably," says Narasimhan. ⊕