Paint roofs white and cool the earthSeptember 14, 2008
Your roof colour matters
|California already mandates a white roof for its buildings but if it makes energy sense and economic sense, white insulating and reflective roofs should become a matter of choice rather than being imposed through legislation.|
— Photo: M. Moorthy
Practical: Coating on ceiling reduces heat inside a building.
If you ask Hashem Akbari the one thing that he would do to save the planet from the ill-effects of global warming, he would say paint the roofs of the homes of 100 of the world’s largest cities white and change the road surface to a light colour. Who is Hashem Akbari? He is a physicist and part of the heat island group at Ernesto Orlando Lawrence Berkeley National Laboratory and was presenting a paper at the fifth annual climate change conference in Sacramento, California, on September 9, 2008. (His website is at http://heatisland.lbl.gov/ for those who need more info).
White reflective roofs
It is well known that roofs are the largest heat gainers in buildings and also that if the roofs are painted white they would reflect a large percentage of the incident solar radiation, especially the infra red radiation, away and keep the building cooler. A good reflective white paint brand like the Australian paint called Insultec, claims to reradiate 95 per cent of the infra red rays and 85 per cent of the ultra violet rays, thus reducing the heat load inside the building by 30 per cent. This can reduce air-conditioning costs considerably in buildings. These insulating paints also have the advantage of being water proof and prevent the conduction of heat also.
They can normally be applied on any surface including RCC roof surface, tiles, asbestos sheets and even on poly-coated sheets. Costs are supposed to range from Rs. 40 to Rs. 50 a square foot .
While at an individual building level there is a saving in electricity consumption and having a cooler building, Hashem Akbari adds it up by arguing that lower power consumption means lesser requirement from power plants and therefore lesser generation of CO2 and NOx by the power plants, therefore contributing to the lessening of global warming. Each building can therefore contribute in its own way to lesser emissions from power plants.
Cut in emissions
A 1000 sq. ft. of roof area, a typical roof on an average 30 x 40 site in Bengaluru, painted white can offset 10 metric tonnes of carbon dioxide emissions as compared to a dark roof, say with tiles.
Consider this: 44 metric gigatons of carbon dioxide and other green house gases would be offset if the world’s 100 largest cities converted their roofs to white and made their roads lighter.
California already mandates a white roof for its buildings but if it makes energy sense and economic sense white insulating and reflective roofs should become a matter of choice rather than being imposed through legislation. Asphalted and tarred roads are dark in colour and absorb heat as any two-wheel driver will tell you during summer time. Roads which are dark and blacktopped can also be changed to lighter coloured and more reflective concrete roads.
Since roads make up 25 to 35 per cent of a layout or a city, changing their colour to lighter shades and increasing their reflectivity will cool the immediate surroundings by 2 to 3 degrees Celsius and also contribute to power savings. The importance of avenue plantations and tree shading on both roads and buildings cannot be re-emphasised.
Not only does it contribute to the micro-environment and biodiversity but there is increasing evidence that on a larger scale this can reduce global warming.
Good reflective and insulating paints on the roofs also have another advantage on roof and water. They can be cleaned easily. Their runoff coefficient — the amount of rain that runoff during rains — is higher; therefore, more rainwater can be harvested from such roofs. When the paints are made of inert material and are non-toxic the run-off water quality is also improved and this rainwater can be harvested and even used for drinking.
Thinking smart about roofs helps the building, the earth and water. The roof above your head not only protects the individuals inside but can contribute to solve problems related to water, energy and global warming.
In a city, smart roofs are the path to water wisdom.