Studies estimate that 1 square metre of grassed rooftop can remove up to 2kg of polluted particles from the air every year, depending on the foliage type.
By definition a green roof can be:
- A layer of living vegetation that is installed on the top of a conventional flat or sloping roof;
- An extension of the existing roof which involves a high quality water proofing and root repellent system, a drainage system, filter cloth, a lightweight growing medium and plants;
- A roof that has a suitable gradient that is planted with low growing, drought resistant, indigenous vegetation in a shallow, lightweight growing medium.
Looking to the future
With the numerous benefits green roofs provide (see Greening our cities Part 1) it is unsurprising that despite the economic downturn of 2008, the green roof industry grew by over 16% through 2009. But green roofs are by no means mainstream in city living. At least not yet. Nevertheless, initiatives such as the eThewini Municipality Pilot Project have demonstrated that while nothing innovative and visionary is easy, the benefits of rooftop gardens for urban living are very real. Perhaps a shift in mindset to broaden our horizons about how to green our lives is needed. When it comes to rooftop gardens, the change will clearly take place above us, rather than beneath our feet.
Growing green roofs in Durban
As part of their climate protection program, eThekwini Municipality embarked on an impressive green roof pilot project dubbed as one of the municipality’s most innovative ventures to date. The project is a response to higher temperatures and increases in the frequency and severity of floods and droughts experienced in the region. The project aims to reduce temperatures and storm water runoff; mitigate and adapt to climate change; promote inner city biodiversity; and address food security issues.
The pilot site is one of the buildings in Durban’s Engineers’ complex, which was chosen because the roof is flat and easy to access; and in a secure location where scientific studies can be conducted.
Successes of the Green Roof Pilot Project
- Temperature probes show up to a 25°C reduction in the temperature of the green roof versus a traditional blank roof.
- Results to date have measured a 100 litre reduction in stormwater flowing off the green roof versus the standard roof.
- A biodiversity study done within the first year of the Green Roof Pilot Project concluded that a healthy ecosystem was developing on the roof with some 66 different species being found.
The largest green roof project in the world is just outside Madrid, on the roofs of a bank, Banco di Santader, and covers more than 10000 square metres. The roof offers natural beauty for business meetings and creative office breaks for employees who now enjoy a motivational and inspirational working environment. The installation of this green roof has improved waterproofing, water retention and enhanced the local climate. In summer months, the green roof has naturally lowered the building’s indoor temperatures.
Winner of the Australian Award for urban Design, the City of Sydney’s renewal of Paddington Reservoir Gardens has injected life into a historic site and revitalised a rundown inner city. The park on the reservoir roof was completely reconstructed and a new sunken garden was installed that engages the public and has created a new space for community activities. The ruins of the reservoir, which date back to 1886, have been converted into a tree fern garden while two other roof gardens were planted with native grasses.
Sky vegetables is an award-winning business idea that came first place in the 2008 business plant competition at the University of Wisconsin-Madison. The business constructs and operates 12 month growing systems on urban rooftops. The produce is grown year round in specially designed hydroponic greenhouses tailored to fit the specific properties. Once ripe, the produce is picked and distributed for local sale. Video cameras have been installed in greenhouses to send live feed to produce departments in the lower sections of the buildings. The buildings are also fitted with wind turbines and solar panels to enhance energy savings as well as composting kits to reuse organic matter and plant materials for growing mediums on the roofs.
This is the epitome of innovation for sustainability that achieves commercially viable urban rooftops, improves the health of city inhabitants and provides jobs and educational opportunities through city greening.
Source: Simply Green Greening our cities (Alexis Schaffler)
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