As buildings continue to battle for ground space in urban areas, vegetation is continually being replaced by asphalt and concrete. Greening the roof seems to be a viable method to explore landscaping. Emerging “smart” roof technologies include vegetative roofs, building integrated solar membranes, bio-based roofing materials with increased recycled content and increased concepts of material re-use. Traditional roof gardens require a reasonable depth of soil to grow plants and are labour-intensive, requiring irrigation and continued fertilizer feeding. As an alternative, one can opt for straightforward innovative techniques for a rooftop garden producing equivalent output.

Retrofit measures

Exnora International has developed numerous methods that can be adopted by existing homes eliminating the need for major structural modifications and waterproofing. Discarded materials serve as ideal containers for plants in a variety of innovative ways. For instance, a stepped-up platform using wooden posts, planks, aluminium sheets can create an elevated podium for growing shrubbery. Strings of coir woven together can be hung between two poles for climbers to creep on, forming a vertical green backdrop along the terrace periphery. Boxes and bottle crates stacked in a zigzag manner, drums and large perforated containers can also be utilised.

M.B. Nirmal, founder, Exnora International, says “The rooftop offers one compensatory space to explore various eco-friendly terrace farming techniques. With less time and work needed for maintenance, it makes gardening more simple and stress-free. A variety of vegetables and fruits can be organically grown. In addition, it also offers an increased habitat for native bees and butterflies.”

The terrace also offers an ideal ventilated space for aerobic composting, an efficient form of composting from the chemical point of view as it produces energy only in the form of waste heat, carbon-dioxide and water.

“Vertical composting can be done in cylindrical bins on the terrace of large apartment complexes where space is limited and the organic manure can be used to nourish the plants. It works as a symbiotic process. Flowering plants, creepers, medicinal plants thrive well in these conditions. One can innovate and create a garden on the terrace using materials otherwise disposed of as waste. For example, earthen pots, polythene bags and broken pipes can all be used effectively to accommodate them”, he elaborates.

For newer construction, "extensive" green roofs can be designed at the planning stage, accommodating adequate structural requirements and water tightness. “One must take into account the weight of installed items like pots, pipes, plant bed in the form of earth, sand, red sand and manure and the weight of plants which will grow”, says an architect.

Established on a layer of "soil" or a thin layer of rock-wool laid directly onto a watertight membrane, the depth of growing medium can vary from a few centimetres up to a maximum of around 10cm. They are lightweight and require nominal structural support from the building. Since the vegetation is adapted to the extreme roof top environment, they are self-sustaining, require minimal maintenance and resource inputs. Annual weeding processes and an application of slow-release fertilizer embedded in a medium to boost growth are mandatory. Mosses and Sedum species are some of the most common plantings.

Advantages

Compared to regular roofing material, green roofs do a better job of insulating buildings and lowering interior temperatures. Savings on energy costs, depending on the size of the building, climate and type of green roof prove economical in the long run. Green roofs also substantially reduce rain runoff onto streets and into storm drains. Water is stored by the substrate medium and taken up by the plants from where it is returned to the atmosphere through transpiration and evaporation.

In a larger context, a green roof will have a noticeable impact on the heat gain and loss of a building, as well as the humidity, air quality and reflected heat in the surrounding neighbourhood.

A lush rooftop can provide effective amenity space for building users in high rise buildings — in effect replacing a front garden. By recovering lost ground space on the roof, users can benefit from the versatile applications employed on the terrace. It can provide amenity space for meetings and recreation.

An accessible green roof can thus improve the aesthetic appeal; increase the value of the property and the marketability of the building as a whole. Green roof technologies not only provide the owners of buildings with a proven return on investment, but also represent opportunities for significant social, economic and environmental benefits, particularly in metropolitan cities.