Let us have green and cool roofs
The focus area of the ‘Green Sense’ column has been eco-friendly and energy-efficient ideas towards sustainable futures. Vegetative garden is being discussed here as one of the means of achieving that objective, including passive cooling of buildings.
Going by the mail response ‘Green Sense’ column received during the last few weeks, one wonders why we do not get to do what is close to our dreams. The terrace suddenly appears to be a potential unexplored, with pavilions and gardening being what many house owners dream of! If it is true, we need to realise what has been the obstacle for following one’s dreams and find corrective solutions.
Incidentally, the focus area of Green Sense has been eco-friendly and energy-efficient ideas towards sustainable futures; as such, vegetative garden is being discussed here as one of the means of achieving that objective, including passive cooling of buildings. This idea of terrace garden is not to force residents to divert their time towards vegetable cultivation. We are living in the age of busy schedules, with no spare time; as such, expecting everyone to grow vegetables as a weekly norm surely sounds far fetched.
So, when a reader responds asking how practical it is to expect people to do rooftop vegetation, the answer can be guessed without stating it. However, there could be many people who generally stay at home, who may take to it as a pleasurable hobby. Having said this, we need to discuss vegetative roofs, not only for the ecological benefit, but equally well for the multiple advantages they offer — exercise for the body, livelihood for gardeners, home-grown vegetables or a place for family relaxation.
In case it is an existing building with no hollow core slab and we have no time to do greening of the roof, what do we do? Give up on passive cooling? Not really, there are other excellent ideas such as painting the roof white. This cool roof concept comes from the proven fact that white colour reflects light and absorbs less heat, hence keeps the building interiors cooler. Nowadays, the cool roof concept is being popularised in green building circles, it being the easiest step towards reducing heat gain in buildings. There are special paints available which are made to reflect more heat; however they may cost more.
The traditional lime wash
Traditionally, many villages in hot, arid regions are known to lime wash the house walls and often the roof also every year as a festive preparation. This practice might have begun both as a strategy of annual maintenance and also passive cooling. Lime being a common material and economical, a coat of white lime with small quantities of blue to tone down white-brightness and a pinch of salt to increase surface density of particles is among the simplest, cheapest, and easiest solutions in the Indian sub-continent.
Unfortunately, this century-old wisdom is also among the ideas vanishing at the fastest rate, since no manufacturer, no company, no advertisement and no website is promoting local lime coat!