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The Flowering Roof

Grow a garden or a lawn on your terrace to beat the heat, but do not neglect maintenance issues.

22bgpgreensenseGJE1KCLVU3jpgjpgWith the summer temperatures soaring high, everyone dreams of cooler homes. Air conditioners could be a solution, but we now know that they are not a solution, but a villain.

For innumerable reasons like the way they transfer indoor heat to outside increasing city temperatures, dilute our biological capacity to live with seasons, health problems due to moving across high and low temperatures, artificiality of air, poor indoor air quality, power consumption, electricity bills and such others, AC has proven to be anti-environment and anti-health.

Given this, there has been increased search for simple and natural solutions. One among them is a green roof, not growing vegetables in trays, but having greenery all over. Imagine a roof where we see no concrete, but only grass! It increases thermal mass, delays surface run-off and works with minimal maintenance.

An intensive green roof needs to be structurally designed for load, or if we plan to grow on the existing roof, a qualified engineer can assess its feasibility. In case roots attempt to penetrate the concrete, a root barrier layer of High Density Polyethylene (HDPE) or any other suited sheet can be laid, though the best is to ensure that shallow rooted plant material are chosen. Additionally, HDPE also ensures water proofing.

Above the root barrier, a drainage layer is needed with half-inch of gravel and a layer of sand above it. To ensure the mud does not slip into this layer but only excess rain water does, we can use the costlier but more long lasting geothermal fabrics or simply save money by using shade nets. They let water down but not the soil. Finally, we need red soil, manure media or mud mixed with perlite, vermiculite or coco peat. While all these are suited for plant growth, the decision may depend upon possible roof load, maintenance issues or available water.

Typically, the soil layer can be 4 to 8 inches thick based on plants’ type. Parapet wall height may have to be adjusted to take the terrace garden and multiple drain holes will be needed compared to what we normally provide. Drip irrigation can be implemented in case of large roof areas.

While lawn would be the choice of most people, it demands much water and maintenance, besides many turf varieties not being suited on the terrace. In case of good sunlight, Bermuda, Doob or Korean grass may work, if not St. Augustine may have to be preferred. If the terrace has occasional use, hardy creepers like Rangoon creeper can enliven the surface with its seasonal flowers. With good drainage, ground hugging shrubbery and small water succulent plants can also be considered, which may be easier for de-weeding.

Tray-based roof garden is more popular considering the variety of vegetables one can grow and manage rain water harvesting as well. However, everyone cannot spare time to that end, but everyone can enjoy a lawn or a creeper bed on the terrace.

Terrace treat

Use the terrace to turn a typical building into a green building.

20bgp-terrace-g_GM_2979433eThe potentials of a home terrace is surely among the major new discoveries today in urban areas. While the traditional sloping roofs, especially in tiles or stone slabs, continues to be sustainable, it is not available for anything more than shelter.

The later version of sloping roof in reinforced cement concrete is not only high on embodied energy, but is also prone to increased life cycle costs.

The via media solution of flat RCC roofs has been very popular during the recent decades, but they were left largely vacant but for the overhead water tank.

The major problem with flat RCC roofs has been the solar heat gain – both on surface and inside the room – due to the direct solar incidence. RCC being a dense material with high temperature conductivity, creating thermal comfort in the indoors is a great challenge.

Given this context, let us imagine growing an organic vegetable garden atop. While there have been many groups and initiatives that have promoted terrace gardening, their primary purpose has not been from architectural intentions.

Even if it for growing own food, terrace vegetable farming keeps the indoors cool thanks to micro shading of terrace slab and reducing solar radiation on the surface.

As solar power technology was discovered, the first additional use loaded on to the terraces was heating the water for bathing purposes.

In most cities across India today, solar water heaters on the skyline is a common sight, with Bengaluru possibly with maximum installations.

Turbo-ventilator

Turbo-ventilator is among the new great inventions, which when fixed at terrace level, sucks out the warmer and stale air from indoors, without using any electric power. Priced at an affordable range, it has virtually no life cycle cost, yet ensures the building gets fresh air from outside the whole day.

Solar panels

With electric power getting increasingly erratic and solar technology becoming cheaper, lighting up the building with solar power has gained popularity. Considering the size of the panels and the specific south-facing angle they need, these panels may take up a sizeable area of the terrace. Raising them up as a pavilion roof is now happening, to get the twin advantage of a covered area and perfect fit for the panels.

Skylights

Nowadays, we also have roof-top skylights, the modern version of traditional courtyard opening. Though every modern building does not have one, a large number of structures today have a skylight. Also commonly found are varied methods of rainwater harvesting from the terrace.

Simply totalling all these, we realise there can be half-a-dozen or more interventions on the terrace which will turn a typical building into a green building.

Of course, the sceptic would ask – are all these really possible on a terrace? Dr. Uma and architect Vijayakumar living in Tiruchi say ‘yes’ and their small house terrace is a learning ground for eco-enthusiasts.

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.

Don’t let the building be a box

If the house has no natural air movement, the only option left is to have exhausts and ceiling fans and keep them on all the time.

Let all rooms open into the garden

The Green Sense column explores just one theme in each essay, which makes it easy to read and comprehend. In the process, it singles out issues, which ideally cannot be so separated, being part of the whole process of building. Material cannot be discussed without reference to external elevation; windows affect internal functionality; and semi-open spaces need to relate to the building plan at large.

As such, without the opportunity of an inter-related narration in long text, this column is limited to information coming in bits and pieces, and it is hoped that the reader would connect them together. Often, it may be difficult to inter-relate the topics, where the specific eco-theme stands in isolation, and may never get applied. Hence all of the above explanation and the following text to illustrate the case of window positions and plan form.

Air movement

One of the reader inquiries mentioned about a newly built house, wondering how to increase air movement. Look at most of city houses built within a specific rectangular site. The building form too happens to be a rectangle, add two floors with a flat roof, imagine a balcony or some terrace – at first look it is a rectangular box.

Most rooms have only one external wall, where we end up having one big window in the centre of wall, hoping the size of window would solve all our problems of light and air! In addition, all rooms would have walls and doors, which block the little light and slight air that may filter into the room, resulting in no air movement across the house at all.

We are not criticising the conventional approach, but hoping to learn from it. We realise, enabling air and light is also a function of the house plan; hence there could be one plan that increases air and another that hinders it.

If the house is already built with no thoughts on natural air movement, the only option left it is to have mechanical means like exhausts and ceiling fans and keep them on all the time.

Don’t get rigid in your plans

Instead, let us imagine a house plan where the external wall is not one straight line, plan not a rigid rectangle and the whole house not a box. Imagine one bedroom jetting out by 3 or 4 feet where the window can happen in three directions. Automatically, air movement increases. In case we insert a small garden within the rectangle plan, it would get three walls around it and accordingly there could be three rooms or spaces opening into this garden. Since this open space is within the rectangle, it will not be visible from the road, providing privacy during the use of garden.

Even if the neighbour builds close to the compound wall, there would be light filtering in from this private garden setback.

If such ideas get extended further, what do we get? It would be a building with walls projecting or receding and an attractive overall form. There would be more light and air, achieved not merely by the windows, but by the plan itself.