Cool it, easily

Discover how village roofs can naturally cool interiors, reducing heat transfer and offering sustainable solutions for hot climates.

When we go to villages, we often see kutcha roofs, which primarily contain a medley of many overlapping items — broken chairs, part of a cement sheet, coconut leaves drying up, faded tarpaulin sheets, and grass mats and baskets torn apart. There is no sign of aesthetics anywhere. But do we realise how people keep the indoors cool?

Heat moves through the air by a process called convection and through solids by what’s called conduction. Let us analyse this reference to the village roofs. Maximum indoor warming happens from the roof getting heated up, technically called direct solar radiation or incidence, which, on average for India, is around 4 – 7 kWh/sqm/day. Of course, this figure varies as per place and time but is generally high since we live in a tropical country.

We cannot stop the heat from entering the house along with air through doors and windows unless we can live with still air or no body-level breeze. Alternatively, install air conditioners, which are bad for health, wealth and the Earth - not a sustainable, eco-friendly option.

However, we can reduce heat transfer through roof conduction by simply ensuring the final roof surface is adequately shaded. What the medley of waste materials on a village house does is this simple act of shading reasonably efficiently. Once we let the surface heat up, then it’s challenging to stop heat transfer indoors. We can try cavity roofs, which are more technical to build, costly and less effective.

Shading the roof can be achieved by many means. In coastal south India, it is common now to see a sloping metal sheet roof over the flat RCC roof on many houses. Of course, expensive with a whole roof installed, but the covered terrace can serve as a multifunctional space across the year. During rains, the sides of the terrace may get wet but will not dry up with no direct sunlight, leading to other related problems. Wetting the surface also has similar side effects while cooling the indoors.

Suppose we are seeking temporary solutions just for a few weeks or months, like what Bengaluru needs. In that case, the flat terrace surface can be covered with anything readily available, like discarded pine wood pellets from shipping containers, coconut tree leaves, any unwanted sheet roofing or such items. This approach would make the terrace unusable, hopefully acceptable for those hot days.

Passive cooling by simple solutions can quickly bring down indoor temperatures by many degrees, which can then complement the active cooling by air conditioners, if we are still bent upon using AC, still saving us money! The point is that our solutions for a month’s problem need not be permanent, lasting for decades. We can cool it easily.