Paint the town white!

Summers are getting hotter. Air Conditioners are expensive. So are energy bills - which makes ACs un-affordable for many. Painting the roof white is a low cost solution to beat the heat relatively. This is for rooms and spaces where the roof is exposed to direct Sun light. A little bit of tech gyan first. Heat and light from the Sun travel together. A body is black in color because it absorbs all light falling on it. Hence it absorbs all heat too. A white body on the other hand reflects all light (and so heat) falling on it. In simple words, white is coolest, black is hottest. A dark concrete roof absorbs and transmits a lot of heat during daytime and also radiates during the evening. On the other hand a reflective surface like white painted roof reflects away the light and heat and is often several degrees cooler. Indoors can become 10-15 degrees (Celsius) cooler after being coated with white paint. The hot oven-like feeling on entering rooms during afternoon and evening can be eliminated using this technique. For buildings having air conditioning, energy bills will reduce as it takes lesser energy(also less power plants, less CO2) to cool a cooler room than a hot one. 

White roofs can also help reduce global warming too. According to a research by Department of Energy, USA, white roofs not only reduce air conditioning loads of a building but also help reflect back the solar irradiation back to space. Darker surfaces on the other hand absorb the heat during Sun shine, and radiate it afterwards making cities and the surroundings hot. This is urban heat island effect. These radiations being in different wavelength than the ones incident are not rejected back to space. Studies suggest that if roofs of all buildings in the whole world are painted white, global warming can be reverted. Yes, lower energy bills, a comfortable interior & also saves the environment.

The options:

White paints come in different forms. Traditionally limestone(choona) mixed with adhesive is available commercially in India. Lime is cheap and easy to apply. Other alternative is white cement paint, which is affordable and also is slightly better in resisting rains than lime. Do note that these two paints have to re-coated every year. Another alternative is elastomeric paints. Some Indian brands like ICI Dulux and Berger Paints sell it. These paints form a rubber like stretchable membrane on the surface and are highly resistive to rains. It can last 3-5 years. The downside is that it costs a lot, generally 20 rupees per square feet area. In contrast, lime and cement paint come at around just 1-2 rupees per sqft including labor charges.  

A permanent but expensive alternative is white ceramic tiles. They come at 50-60 rupees per sqft at the least. They can last a lifetime and are much easier to clean, and your terrace looks beautiful too. The roof can be water proof too if grouted properly. It provides an all year cooling as paints are usually washed after rains, and in our tropical climate, we often need air conditioning for more than 6 months in the year. Any white surface (both paints and tiles) provide a longer life to the roof, as expansion and contraction due to heat is greatly reduced. Crack formations are minimized too. Solar Reflectance Index (SRI) values on commercial products are a good way to compare - higher the better. For tiles, vitrified variety is better suited to outdoors due to lower water absorption capacity. 

White is the new green. Cars too in white color save fuel as compared to black ones. Yes your walls and everything exposed to Sun is better off in white. We do white cement paint every year and it is a big relief in this sultry Odisha heat. We have temperatures touching 45 degrees Celsius every summer. White paint works beautifully here. Let us know if you have done it, your experience or any questions if you have - we will be happy to answer them. So cool interiors, climate change arrest, longer roof life – when are you going white?