The sun glares down and seems set on keeping its fiery glance focussed on us. At times, the sweltering heat makes us sweat even in ventilated indoor spaces. To beat the heat, many of us turn to air-conditioners, which guzzle electricity, making our hearts skip a beat when it’s time to pay the energy bills. It makes sense to shield our buildings from heat gain rather than negate it later. So, is there a heat shield for buildings?
Well, as simple a decision as your colour choice in exterior paints can make a big difference. White wins this battle, hands down. Though, of course, you can take a little leeway and try off-white, ivory, and other shades of white. Opting for a house bathed in white ensures maximum reflection of the heat rays that hit the house. On the other hand, the darker the shade of paint on exterior surfaces, the more is the absorption of heat.
In fact, the White Roof Project (WRP) taken up in cities like New York has shown that heat reflective white roofs can make a world of difference to both short-term and long-term climate change concerns. This project was started as a go-green endeavour to reduce carbon emissions caused by indoor air-cooling, reduce stress on the power grid and save on electricity usage for cooling. Volunteers undertook the task of white-painting roofs of buildings in New York City neighbourhoods like Manhattan. “This ended up making substantial money savings for end users too, prompting many building owners to pay up for white-painting their roofs,” points out S. Aarthy, energy consultant.
The White Roof Project estimates that a roof covered with solar-reflective white paint could also reduce ambient heat in urban outdoor spaces by a few degrees and partly mitigate the ‘heat island’ effect. “In fact, it is estimated that 5–10 per cent of summer electricity is used just to negate heat gained by buildings because of the heat Island effect”, remarks R. Saravana Perumal, hybrid green home consultant. Add to this the electricity used for further cooling of indoor spaces, and the importance of going in for white roofs becomes self-evident. No wonder, WRP has now grown into a global network with chapters in various cities. “White surfaces absorb just 35 to 50 per cent of heat falling on it, and retain less than 7 per cent of the absorbed heat. And over 90 per cent of the little heat that's absorbed is reflected back into the atmosphere.
On the other hand, black surfaces absorb about 90 per cent of heat, and also retain 50-60 per cent of this absorbed heat. That is the reason cricketers playing in the sun dress in white flannels, and doctors advise wearing light coloured clothes in summer,” points out R. Saravana Perumal. Remember, our traditional village huts did manage to stay cool even without fans, leave alone air conditioners, thanks to their white, lime-washed walls and thatched roofs. By white painting, we can make 25 per cent energy savings on air conditioning, and 10-15 per cent on fan usage. White paint causes much less carbon emissions too compared to coloured paint.
“Simple exterior white emulsion paints and even inexpensive whitewashing or lime-washing works quite well, though, of course, there are special paints with higher solar reflectance index (SRI), and white-hued insulating tiles in the market. But again, special paints may have added chemicals which are perhaps better avoided. Keep the ceilings white too,” says Perumal. By preventing heat gain into the building structure, we also get to prevent cracks erupting on walls because of heat-triggered expansion of cement.