Cool Roof for Cool Cities

Anamika & Tanmay Tathagat Environmental Design Solutions Pvt. Ltd.

Anyone who has lived on the uppermost floor of a building, may have experienced the discomfort of significantly higher temperatures during the summer months compared to other floors in the building. Many modern buildings in India are constructed of concrete or cinder blocks and are topped with flat, tar-covered roofing. Such surfaces absorb the incident sunlight, transferring it to the interiors of the building. The hot ceiling continues to heat up the space – during the day and well into the night - making the spaces unbearably hot throughout the summer season.

Figure 1, a thermal image# of a typical top floor roof on a summer day, clearly shows the large temperature difference between the inside of the roof and other surfaces in the room. While the surrounding spaces are cooler at around 34-36˚C, the ceiling temperature ranges from 39-41˚C. The heavy mass of the concrete roof stores the heat and re-radiates it to the inside. The exposed surface of the roof can get even hotter, with dark surfaces attaining temperatures as high as 80˚C.

#Thermal imaging involves the use of a special thermal camera, which operates within the thermal infrared spectrum to measure the amount of heat that an object is emitting. In such pictures, temperature is indicated by a colour code, such as dark blue for low temperatures and red for higher temperatures. for example in Figure one can see the hot engine exhaust of a jet, indicated by a warmer red color as opposed to the cooler sky around, indicated by the blue color.