In future, will greater numbers of people cultivate food and take outdoor exercise or lunch breaks in the sky? The idea of gardens above – instead of below – has been around since Nebuchadnezzar II purportedly built the Hanging Gardens of Babylon some time in the first century BC, but they have tended to be a glamorous and expensive novelty. However, today in city centres around the globe, green rooftop spaces are proliferating.
For the first time in history, the number of people living in cities rose to more than 50% of the world’s population in 2008. This figure is set to increase to 75% by 2050, according to the United Nations. As cities become denser, how urban spaces are designed and managed so that city populations and the environments that support them continue to thrive is obviously a major concern for architects, city planners, businesses and residents alike.
Challenges posed by population density go hand in hand with those posed by climate change and the requirement for cleaner and more efficient energy use. According to a survey by worldwide property management and construction company Lend Lease, buildings account for 40% of the world’s global greenhouse gas emissions and use 12% of the world’s water.
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Green roofs are part of an integrated response that may include solar panels, grey water recycling and other sustainable features to reduce the carbon footprint of a building. Green roofs have been shown to provide insulating qualities, cooling buildings in summer and keeping them warm in winter. They can also reduce stormwater run-off through natural absorption and filtration, contributing to cleaner air and improved public health and wellbeing. Less tangible benefits are also coming under scrutiny with Green Star-rated buildings showing that it’s not just the environmental benefits but also the social and economic side that is driving this trend. “Increasingly evidence shows that there is a strong link between greener buildings and their indoor environment quality to occupant perception and satisfaction and productivity,” says Deo Prasad, program director of the Built Environment Master of Sustainable Development program at the University of New South Wales (UNSW).
Many of Australia’s cities are now working towards sustainability targets and green roofs are part of that drive with federal government legislation adopting a carrot-and-stick approach to steer businesses towards the same goals. In November 2011, the government’s building energy efficiency disclosure laws came into force requiring corporations that are selling or letting large office space to provide a NABERS (National Australian Built Environment Rating System) certification and energy rating for their buildings.
Green, greener, greenest…
Some businesses do not need much pushing. Construction company Grocon’s new Pixel building in Melbourne is the first completely carbon neutral building in Australia. It has a green roof planted with Victorian native grassland species, wind turbines and solar panels, and has achieved the highest-ever green star environmental rating. A vast desalination project also underway in Victoria is set to have the largest living green roof in the southern hemisphere.
Among the Australian capitals, Adelaide has had the greatest concentration of green roof research and development to date, and the South Australian state government has lead the way in promoting green infrastructure. A series of green roofs and walls has been constructed, aiming to mimic the ecosystem of the original landscape by planting native species and creating corridors for wildlife to pass through.
Graeme Hopkins, UNSW architecture alumnus and co-author of Living Architecture: Green Roofs and Walls (CSIRO Publishing 2011) worked on one of South Australia’s first green “islands” in 2006. When the state government funded a green garden on top of an Adelaide social housing tower block, Hocking Place, it was seen as a prototype. “It combines having a recreational space with paved areas and seats with bush planting so birds, bees and insects are attracted to the native plants of Adelaide. This added to the benefits of an existing nearby green rooftop with another built 200 metres away, so that started a linkage of green roofs planned for the city,” notes Hopkins.
Adelaide is surrounded by parkland and used to be part of an ancient migration route for animals before the city was built. Hopkins says these aerial corridors have helped to restore that landscape, creating “urban biodiversity.”
The SA government, in association with a commercial developer, is also funding a detailed monitoring program of living wall and green roof trials on a multi-storey building, where temperature, relative humidity, water run-off quality, vegetation performance and CO2 levels are being recorded and analysed to quantify the benefits for building owners and for the city environment.
Although Australia is starting to make strides in its urban green developments, it’s fair to say the nation has lagged Europe, the US and Asia in green roof development, despite its iconic parliament house in the national capital, Canberra, which is one of the most lauded examples of a large-scale living roof anywhere. It is cold climate centres, such as Toronto, Chicago and Germany, where green roof innovation has flourished, spurred on by investment and government legislation.
Asia has the most to teach Australia, asserts Prasad. Places where space is at a premium, such as Japan and Singapore, have a very specific rationale for creating green rooftops. “When you start afresh with some land which has greenery on it, the approach that they have taken is that you should have at least as much greenery on the site when the building goes up as you did before it was built,” Prasad reports.
Hopkins believes a lack of expertise in Australia has held back green roof development as well as outmoded attitudes. “Among older architects – and they own most of the design companies – there’s a resistance; the residual thinking is that green roofs won’t work. Young graduates coming through just want to do it even if they don’t understand the technology of green roofs sufficiently.”
Education needs to catch up with the impetus for change among a younger generation, says Hopkins. “I have an issue with the universities about this. There’s no formal module in any of the architecture or landscape architecture courses. Without designers who understand the principles of this technology, further advances or experimental designs or systems will take longer to develop and infiltrate through the industry.”
There’s a green light at the end of the tunnel though. Hopkins is discussing the development of a course module on green roofs with Linda Corkery, program director in Landscape Architecture at UNSW. Corkery has recently completed a small research project with lecturer Paul Osmond and research associate John Blair on green roofs in Sydney. As part of its Sustainable Sydney 2030 plan, the City of Sydney Council aims to counteract the effects of climate change and reduce energy consumption and wants to know how green roofs can contribute to reaching those goals.
There are around 46 green roof projects of varying size in the City of Sydney, including some over car parks and freeways. Corkery says one question of interest was the motivation for their construction. “Most of the green roofs in the city are on apartment buildings [and] a few are on commercial buildings. For the most part they have been included for recreation or aesthetic value rather than for environmental reasons or climate concerns,” Corkery says.
That’s not to underestimate the importance of the feel-good factor in having a “green retreat” on a building. Corkery says more investigation is required into the psycho-emotional benefits of green roofs. “We know from research in other settings that just having a view of a green space can provide benefits to people’s wellbeing, but it’s very hard to measure and not much research on this has been done in Australia.” We are left instead with positive anecdotal evidence. Daniel Baffsky, the landscape architect responsible for the rooftop garden at M Central in inner city Ultimo, Sydney, says the garden has contributed to a strong community network in the residential building.
“Neighbours meet in the garden, they socialise and relax. Many people in the building own dogs, so rather than walk through the streets of Ultimo after work they can walk them in the safety of the garden. It is their own little slice of paradise,” he says. The building management estimates that approximately a quarter of the residents use the rooftop landscape garden each day.
Similarly, a rooftop garden used as a social hub by office workers sits on top of 30 The Bond in Millers Point, Sydney, completed in 2004 at a cost of A$112 million. A post-occupation survey of staff found that 51% thought they were more productive at work as a result of their new rooftop garden and other green features of the building.
Green roofs generally fall into two categories, extensive and intensive. Extensive green roofs have a soil depth of 150mm or less, support low vegetation and are not suitable for recreational use. Kingston High School in Hobart, Tasmania is a good example with the pupils using the roof to plant indigenous plant species and providing thermal and sound insulation for the buildings underneath. Intensive green roofs are more recreational and have a depth of soil more than 150mm. They are more common in Australia as in extreme heatwave conditions, they are good at retaining moisture.
Neither kind of green roof is a cheap option to build – although exact figures are harder to come by in Australia than they are in the US where the green roof trend is growing more virulently. In 2010, the number of green roofs in the US expanded by 28.5%, a sizeable increase from the 16% increase recorded in 2009, according to greenroofs.org. Figures quoted by the Low Impact Development Center (LID) in the US show that “costs for green roofs in the US are estimated to average between US$15 to US$20 per square foot for all use types: high-density residential, commercial, industrial etc.”LID compares the often customised installation methods in the US to green roof creation in Germany “where an entire service industry has evolved in response to green rooftop development and costs run between US$8 and US$15 per square foot.” It notes there are also ancillary costs to take into account, such as increased insurance and liabilities such as weight, drainage and potential interior damage from roots.
Despite high start-up costs, there are long-term savings. A vegetated roof on average is expected to prolong the life of a conventional roof by 20 years. Combined with energy savings due to the additional installation and potentially increased real estate value, the cost compares favourably to a conventional roof, claim proponents of green rooftops.
Brendan Bateman, a partner at Australian law firm Clayton Utz, advises clients on environmental legislation and upgrades for commercial buildings. Bateman says the demand from tenants for more energy-efficient spaces, roof gardens and green walls is increasing, fuelled by demand for better living and working conditions that will attract the best employees. Studies in the US show that average rents from sustainable buildings can generate up to a 6% higher rate of return.
“Business has to evolve with the new conditions; there are drivers for change in the market that didn’t exist 50 years ago,” says Bateman. “The added benefits that come with green spaces are a better working environment and a greater level of productivity. It has an opportunity to engage at all levels of the business, at board management and staff level. At the end of the day we’re talking not just about environmental sustainability, but also business sustainability.”