What could be the greenest roof above us?
Terraces with shrubs and small trees keep the house cool
The expression ‘heat gain,’ often heard in discourses on green architecture, is actually a human invention. Let us imagine we have no solid roof above us and are outdoors. There is heat of course, but no heat gain as such. This example also holds good if there is only an overhead roof and no walls around us. It’s the act of enclosing space that attracts heat and also, a host of other environmental issues that we all need to rethink about. This is not to negate the need for buildings, since we humans need shelter more than any other animals, but to suggest that our problems could be of our own doing.
What could be the greenest roof above us? Of course, a big tree! Every person in all continents, except at snow-capped regions, knows the comfort under a large tree canopy; the shade in hot dry region; and the breeze in hot, humid areas. Without exceptions, traditional villages are a generous balance between trees and huts. The largest tree in the centre would be the public meeting forum, many other trees around serving numerous social activities ranging from tea shops to temples, while household services happen under the tree in the backyard. The green roof of the tree acts like an extension of the thatch roof of the houses.
Numerous local ideas
People living in flat RCC slab houses have attempted numerous local ideas to save the interiors from high temperatures. While some place potted plants, a few others have virtually nurtured a nursery there. In many houses we can see coconut leaf or other equivalent tree matter spread out. All these are simple examples of roof-top vegetation, which also include growing vegetables or in some rare cases like the house of architect Chitra and Vishwanath, growing rice on the terrace. The conventional images of roof gardens are also part of this thought, though now the idea of a designed and manicured garden for recreation has advanced to include other varieties of plant species. While flowering creepers and soft ground plants are easy to maintain, there now are terraces with shrubs and small trees!
In our context, roof-top vegetation assists in more ways than one: minimises heat gain into the building and reduces heat island effects in the city; facilitates birds and butterflies; controls rainwater run-off; acts as an absorbent of city sounds; creates an attractive look; and on an overall count, conserves energy.
While all this sounds good, we need to take certain precautions before doing extensive terrace vegetation. Vegetative roof is comparatively a new concept, where most of us have no prior experience. Basic acts like placing potted plants is possible right away, but even there draining the excessive water could be an issue. As such, we need to explore more about the problems and potentials associated with green roofs