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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.

Multiple advantages

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!

Walk up to the roof for vegetables

A vegetable garden can be organised on any flat roof.

When we visit our relatives in a village, the way they walk into the backyard, pluck vegetables and cook a delicious meal is enviable to every one of us. We all know that the vegetables we buy from a shop in a city are not fresh, however good the air conditioning in the truck or the shop be. It is not that urban living does not permit time for gardening, but the logistics such as land, manure, pest control and water management act as a deterrent.

But with increased awareness about the organic movement, many house owners have now started growing their own vegetables, though in small quantities.

A typical terrace vegetable garden can be organised on any flat roof with pots. While cement pots are easily available, they tend to absorb heat and make even the mud fill inside slightly hot.

As such, earthen pots are better suited. Between a wider and deeper pot, the deeper one should be chosen with drain hole at the bottom.

Seek advice

Any horticulturist or nursery expert can advice on vegetables that grow well in pots and the kind of preferred sunlight. Fixing light weight shade nets on part of terrace extends the life of plants and increases the yield.

Vegetables of shorter time cycle normally have shallow roots and better enjoyed because of early yields.

The main advantage of growing vegetables on pots is the ease of maintaining them all. Shifting for more sunlight, changing mud mix, doing replanting, changing pots and such other tasks can be handled by any one.

The pots can also be placed on balconies that receive direct sunlight. There are vegetables that grow on creepers, which may find the terrace floor too hot during summers. In such cases, place some dry palm leaves where the creeper is expected to grow into.

The overall weight on roof slab needs to be considered, hence it is safer to line up pots with walking space in between which does not lead to critical point loads on roof.

 More green options

There are many other options to have more green within the building — growing wall climbers such as Ivy, hanging plants and drooping creepers, grassy lawn on sun-lit terrace, creepers on pavilion or pergola roofs turning them into leafy roofs, herbal gardens and such others.

While all these ideas appear good and commonplace, it is always safer to take expert advice at least in the beginning. Dampness in walls and roof could be a predictable problem if the building is not safeguarded against water seepage.

Potted plants require periodic mixing of mud within the pot and total replacement occasionally. Most people living in cities need advice on plant material, sowing period, crop months and plucking time since tghey are totally disconnected from nature.

Terrace gardening is a way to connect to nature again.