Green Roofs
Real Estate

Green Roofs

Serving as a shield in the war between vertical structures and the urban atmosphere, green roofs are the call of the hour, finds Shanti Padukone.

Call them what you like – green roofs, sky gardens, or green terraces – green patches atop roofs or terraces of buildings are here to stay! Adopted primarily for their ability to mitigate the heat island effect in an urban environment, these patches minimise the impact on the micro-climate and living habitat. “Generally, heat is absorbed by roofs and reflected into the environment, further heating the ambient air. In such a scenario, a green roof effectively reduces the temperature ingress. Through greenery, the water used for irrigation absorbs the heat and then evaporates leaving both the surface and ambient air cool,” says M Anand, Senior Counsellor, CII-Sohrabji Godrej Green Business Centre (CII-Godrej GBC).

Green sense

CII-Godrej GBC houses the Indian Green Building Council. It was one of the first commercial buildings in India in 2003 to have a large green roof of its scale. Anand highlights, “In the last eight years that we’ve been operational, we have observed how our green roof has gradually attracted birds and bees to the urban area.” Hence, these turfs can gradually get back some of the bio-diversity that has been lost through extreme concretisation.

Besides, these roofs also serve to cool the interiors of the structure by absorbing the sun’s heat and reducing the roof’s heat conductivity. “This has a consequential effect on the air conditioning load and overall energy consumption,” informs Ashish Rakheja, COO, Spectral Services Consultants Pvt Ltd. Moreover, such roofs act as noise barriers and provide noise insulation for buildings under flight paths.

Furthermore, since plants reduce CO2 levels in the ambient air and overall pollution, used in green roofs, certain species provide more effective carbon sequestering and significantly improve the air quality within the building. Talking about a building in a highly polluted area, Rakheja narrates, “To improve the air quality for its occupants, oxygen-generating plants were grown on the roof, and the fresh air generated into the building improved both the indoor and ambient air quality.”

The installation

Testing the roof’s structural strength is a primary precaution to be taken. According to Suvarna Sathe, Landscape Architect, Sathe Architects, the kind of material used in laying the roof can reduce the overall load. She says, “Earlier, the layering of a green roof involved brickbat coba at the base topped with sand, geotextiles and then mud and manure. But, this would relatively increase the structural load.” Today, drain cells replace brickbat coba and are topped with sand and geotextiles. Above this, a combination of coco peat, vermin compost and a little soil help reduce the overall load by 60 per cent! Of course, waterproofing is mandatory.

Choose your turf

According to Rakheja, green roofs in hot, tropical climates seem to be most effective, while those in colder and more extreme climates may face challenges.

The kind of turf too would vary accordingly. Moreover, Anand emphasises the need to select the ideal green roof according to the general climatic condition of the location. For instance, western states like Maharashtra and Kerala see torrential rainfall for at least a quarter of the year. In such cases, the green roof must be designed to ensure that water doesn’t collect on the top, instead, being immediately drained out to prevent stagnation or seepage. At the same time, Rakheja cautions about the possibility of soil erosion in such turfs on sloping roofs.

The big picture

According to the 2011 census, urbanisation in India is expected to touch 40 per cent by 2021, and 533 infrastructure projects worth Rs 60,544.73 crore have already been sanctioned under the Jawaharlal Nehru National Urban Renewal Mission to meet the consequent demand. And, with this estimated increase in urbanisation, green turfs in the sky (rather than on the ground) seem to make perfect sense.

Cost and statistics

Initial cost of laying a green roof: Rs 60 to Rs 80 per sq ft
Energy savings vs a conventional roof: 10-30 per cent more
Average daily energy demand for space conditioning in a conven-tional roof: 6.0-7.5 kWh
Average daily energy demand in a green roof: <1.5 kWh (Hence, 75 per cent heat flow reduction)
Life of roof fabric: Extended to 70 per cent

(Source: CII-Godrej GBC)

Engineering News Record (ENR) magazine has carried this article in its global digital edition, Global Insider. You can view it on http://enr.construction.com/buildings/sustainability/2012/0709-green-roofs-take-root-in-india.asp

Serving as a shield in the war between vertical structures and the urban atmosphere, green roofs are the call of the hour, finds Shanti Padukone.Call them what you like – green roofs, sky gardens, or green terraces – green patches atop roofs or terraces of buildings are here to stay! Adopted primarily for their ability to mitigate the heat island effect in an urban environment, these patches minimise the impact on the micro-climate and living habitat. “Generally, heat is absorbed by roofs and reflected into the environment, further heating the ambient air. In such a scenario, a green roof effectively reduces the temperature ingress. Through greenery, the water used for irrigation absorbs the heat and then evaporates leaving both the surface and ambient air cool,” says M Anand, Senior Counsellor, CII-Sohrabji Godrej Green Business Centre (CII-Godrej GBC).Green senseCII-Godrej GBC houses the Indian Green Building Council. It was one of the first commercial buildings in India in 2003 to have a large green roof of its scale. Anand highlights, “In the last eight years that we’ve been operational, we have observed how our green roof has gradually attracted birds and bees to the urban area.” Hence, these turfs can gradually get back some of the bio-diversity that has been lost through extreme concretisation.Besides, these roofs also serve to cool the interiors of the structure by absorbing the sun’s heat and reducing the roof’s heat conductivity. “This has a consequential effect on the air conditioning load and overall energy consumption,” informs Ashish Rakheja, COO, Spectral Services Consultants Pvt Ltd. Moreover, such roofs act as noise barriers and provide noise insulation for buildings under flight paths.Furthermore, since plants reduce CO2 levels in the ambient air and overall pollution, used in green roofs, certain species provide more effective carbon sequestering and significantly improve the air quality within the building. Talking about a building in a highly polluted area, Rakheja narrates, “To improve the air quality for its occupants, oxygen-generating plants were grown on the roof, and the fresh air generated into the building improved both the indoor and ambient air quality.”The installationTesting the roof’s structural strength is a primary precaution to be taken. According to Suvarna Sathe, Landscape Architect, Sathe Architects, the kind of material used in laying the roof can reduce the overall load. She says, “Earlier, the layering of a green roof involved brickbat coba at the base topped with sand, geotextiles and then mud and manure. But, this would relatively increase the structural load.” Today, drain cells replace brickbat coba and are topped with sand and geotextiles. Above this, a combination of coco peat, vermin compost and a little soil help reduce the overall load by 60 per cent! Of course, waterproofing is mandatory.Choose your turfAccording to Rakheja, green roofs in hot, tropical climates seem to be most effective, while those in colder and more extreme climates may face challenges.The kind of turf too would vary accordingly. Moreover, Anand emphasises the need to select the ideal green roof according to the general climatic condition of the location. For instance, western states like Maharashtra and Kerala see torrential rainfall for at least a quarter of the year. In such cases, the green roof must be designed to ensure that water doesn’t collect on the top, instead, being immediately drained out to prevent stagnation or seepage. At the same time, Rakheja cautions about the possibility of soil erosion in such turfs on sloping roofs.The big pictureAccording to the 2011 census, urbanisation in India is expected to touch 40 per cent by 2021, and 533 infrastructure projects worth Rs 60,544.73 crore have already been sanctioned under the Jawaharlal Nehru National Urban Renewal Mission to meet the consequent demand. And, with this estimated increase in urbanisation, green turfs in the sky (rather than on the ground) seem to make perfect sense.Cost and statisticsInitial cost of laying a green roof: Rs 60 to Rs 80 per sq ftEnergy savings vs a conventional roof: 10-30 per cent moreAverage daily energy demand for space conditioning in a conven-tional roof: 6.0-7.5 kWh Average daily energy demand in a green roof: <1.5 kWh (Hence, 75 per cent heat flow reduction)Life of roof fabric: Extended to 70 per cent(Source: CII-Godrej GBC)Engineering News Record (ENR) magazine has carried this article in its global digital edition, Global Insider. You can view it on http://enr.construction.com/buildings/sustainability/2012/0709-green-roofs-take-root-in-india.asp

Related Stories

Gold Stories

Hi There!

Now get regular updates from CW Magazine on WhatsApp!

Click on link below, message us with a simple hi, and SAVE our number

You will have subscribed to our Construction News on Whatsapp! Enjoy

+91 81086 03000

Join us Telegram