Monthly Archives: December 2011
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.
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.
Besides the open yard, the only other option to grow greens is on the terrace, which incidentally is not a new idea, if we include the Hanging Gardens of Babylon in the green roof list.
We build on the ground, so theoretically the ground gets transferred to the top of the building. If the ground could have been green, should not the new ground up above also have the options of going green? Of course, yes. Besides the open yard, the only other option to grow greens is on the terrace, which incidentally is not a new idea, if we include the Hanging Gardens of Babylon in the green roof list!
It is the risks involved with roof-top cultivation and lack of remedial solutions for the common problems that makes us leave the roof largely untouched. It is curious that the major driving force today for re-discovering green roofs is not the urge for growing flowers or vegetables, but ecological concerns.
Roof-top plants reduce both the heat gain into the building and heat reflection into the atmosphere, cooling both the building and the city.
Thanks to the evaporative processes, the relative humidity gets a positive boost, though one would need large areas of green roofs to achieve a noticeable difference. If we could begin in a small way today, someday that large area could be achieved.
Three key approaches
There are three basic approaches to greening the roof — plants directly on soil medium; assemblage of potted plants; and softscapes like ground creepers, vines or lawns. Let us first look at the general garden.
Direct planting reaps the maximum benefits, but requires the maximum attention too. The roof needs to be perfectly water proof and preferably designed to take the extra weight of planting. Even if the roof is guaranteed against cracks and leaks, it is advisable to fix a layer of impervious plastic-based lining on the roof top, before filling the surface. It also ensures smoother flow of extra water at the bottom, following watering of plants or long hours of rain.
There have been cases where people tried gardening on existing roofs, with inadequate roof slopes. In such cases, good slopes need to be created during the plastic lining, before the soil fill. If it is an old house, adding a water-proofed concrete layer could be considered before doing extensive gardening.
The patch where we go green and the leftover terrace have to be edged with appropriate materials such as brick on edge. Often, this edge gets ignored and the whole terrace gets wet due to water seepage from the sides!
Lightweight coconut pith compost, peat moss and such manure soil mix are among the better choices. When we do direct planting, it is easier to keep the soil moist, unlike the case of potted plants. Incidentally, the soil mix should not absorb too much water and retain it too, for this increases the load on the roof.
Plants with only fibrous roots are possible as the top soil mix will be just 4 to 6 inches deep. Of course, there are options in shrubs, herbs, flowering plants, crotons, vegetables, orchids, rose, small palms and such others. For those willing to spare their energies, this is a good enough range!
It shades the roof, supports varied activities and adds to the aesthetics.
In any seminar on green architecture, energy conservation in buildings or sustainable ideas, it’s possible that flat RCC terrace gets the lion’s share of the blame for ills such as internal heat gain leading to air conditioning loads, urban temperature build-up contributing to heat island effects, and structural deflections resulting in increased structural costs.
While all these are partly true, blaming the terrace alone is no solution. Incidentally, terraces are such an integral part of the building, yet they get blamed by all for just being on the top!
Much before the advent of modern RCC roofs, flat roofs were very common, without any complaints of heat gain, thanks to the vernacular technology and local materials prevalent those days.
For drying purposes
Terraces were routinely used for drying farm produces, preparing home food items, children playing and of course, sleeping at night. Today, if they are among the causes of ecological distress, the need of the hour is to analyse the causes and mitigate them. One method is to erect a pavilion on top that shades the roof, supports varied activities and adds to the aesthetics.
Everyone would agree that the best of air, view and sense of space happens on the terrace, yet we seldom use it because it is mostly left as an empty floor. Simply facilitate it, the use begins. To that end, all that we need are shade and green!
The pavilion can be a simple sloping tiled roofed structure of desirable dimensions, supported on four brick or pipe pillars in corners. It could also be designed with attractive modern forms and materials, just as a garden pavilion. Provision of benches and seats underneath enhances the usability of the structure.
Being a simple roofed area, they do not cost huge, yet provide the much needed extra space during events, parties or a session of relaxing yoga and meditation. In many houses, such pavilions are routinely used for washing and drying clothes. In case located in front of the building, the pavilions add to the attraction of elevation too!
…and as food courts too
In many public buildings, the roof-top pavilions are an extensive area, serving as food courts, staff congregation areas, cultural performance spaces and such others. However, if built fully to cover the terrace area, the feel of open to sky terrace itself gets lost.
We need to get the best of both, of covered space and open space. Hence, roofing a part of the terrace could be a balancing act, which is like merging a balcony and terrace. Where we need shade for a swing or seat we get it, while the flowering plants may get the sunlight they need.
If the terrace gets shaded by the pavilion and covered by plants, the major complaint of heat gain gets automatically eliminated!
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
Thatched roofs have strong visual character, making them desirable in resorts, retreats and farms.
The making of a thatched roof.
Indian construction scene faced a strange dilemma during the colonial period when the traditional methods got sidelined as kutchha , temporary and undesirable. Incidentally, most of what our elders built was kutchha using local materials. Barring palaces and temples, may be we were a kutchha country! Anyway, the divide between temporary and permanent continues, e.g., even now we need not take local authority permission for kutchha constructions.
Thatched roof, which has been the single largest roof type in India before the advent of new ideas, is amongst the hard hit in the story of kutchha . The widespread prevalence of thatch could be attributed to its perfect fit for rain-fed, warm and humid climate. Easy availability, simple skills required and minimal heat gain made it a popular choice. By default, it is very local, cheap, replaceable, and hence amenable to self-help construction.
In every drive through the countryside of south India and often even in city contexts, we come across thatched roofs. Mature grass reeds are selected, surface cleaned, seasoned with slight wetting which also make them pliable, sun dried to get the desired water content and then tied together as small mats. Such mats are then tied to the bamboo or wooden purlin below. Additional layers of grass are laid, tying them occasionally to the lower layer. Coconut or arecanut leafs are also used likewise, as an alternative to thatch. Often, the woven coconut leaf is the underside for thatch.
In many modern versions, there are structures with G.I. sheet roofing as the underside; then topped with thatch. This clears the fear of fire and rodents. Grass reeds can be tied together like broom sticks, topped on each other to get a very dense roof layer, which lasts many years. A horizontal projection at the wall top eliminates rats and snake movements. The major complaint against thatch has been its fire safety. Chemically-treated thatch has been attempted, which increases the fire resistance. However, it is better to leave thatch as it is, and have a fire-graded underside which localises the fire, in case it occurs.
Thatched roofs have reduced, yet continue to be among the best options, given certain criteria. Their strong visual character makes them desirable in resorts, retreats and farms. Being temporary, the choice of continuing or replacing them is open after 6 to 10 years, the average life span of a well-done roof, with nearly 30 degrees slope angle.
The highlight of thatch in these days of climate change could be that they are, by far, the most sustainable roof form.
In many villages, thatched roofs are still being made, but if not supported, no person with skills for making thatch roofs would be around in the generations to come. We may lose the most eco-friendly roof to the annals of history.