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View from the top
 The Vikings covered their dwellings in turf, and the ancient Egyptians grew plants and food on their rooftops.
The green roof is not a new concept; but it is only in recent years it has found a place in the building industry.
Today’s green roofs form an extension of an existing roof, with a waterproofing and root-repellent system, a drainage system, filter cloth, a lightweight growing medium and plants and turf.
Modern structural skeletons and profile systems have overcome load-capacity issues, making green roofs suitable for almost any structure, from skyscrapers to single dwellings.
Over the past 20 years green roofs have become an integral part of city planning and architectural design in many parts of Europe, notably Germany and the Netherlands. In the past five years the movement has also taken hold in North America, where 230,000m² of rooftop garden was installed on commercial buildings in 2005.
High-profile green roofs in the US include Chicago City Hall, the Rockefeller Centre in New York and the Ford Truck Assembly Plant in Michigan.
In other countries – Japan, China, Singapore, Canada and the UK – green roof movements are also taking hold. China is reportedly planning for 45% greenery coverage by 2008, and Singapore recently unveiled a green roof atop the School of Art and Design.
Australia’s green roofs are few and far between. Sites include the famously sustainable CH2 Melbourne City Council headquarters building in Melbourne, Lend Lease headquarters at 30 The Bond in Sydney, and Australand’s Freshwater Place apartment building in Southbank, Melbourne.
The Green Roofs for Healthy Australian Cities movement (GRHAC) is hoping this will change soon, starting with Brisbane.
Following the GRHAC conference earlier this year, Brisbane City Council announced in April that green roofs would form a key component of its climate change action plan. The council’s response will begin with green roof demonstrations (it has asked for six potential sites; GRHAC has so far found 18) and supporting research programs.
GROWING BENEFITS
Fighting climate change is one clear green roof benefit. In the most basic of terms, more trees and plants means less carbon dioxide in the atmosphere and cleaner air.
At another level, green roofs provide thermal insulation; reducing the fossil fuels required to heat and cool buildings artificially. They also reduce the ambient temperature in cities caused by the ‘heat island’ effect of buildings and roads, which can leave cities up to 10ºC hotter than rural areas close by.
Other environmental benefits include cleaner water. Because harmful airborne particles are absorbed by the gardens, water harvested from the roof is cleaner than street runoff. Green roofs also provide opportunities for water recycling and catchment areas.
GRHAC founder and director Geoff Wilson says in order to make a real difference green roof action needs to be deliberate and widespread.
“With rapid urbanisation around the world, and rapid onset of climate change problems, government leadership on green roofs is vital.
“Australian cities now need terraforming – so that they become part of a climate-change response rather than being one cause of it.
“Terraforming is ‘earth-shaping’ of a planet, moon or other body. It is the hypothetical process of deliberately modifying atmosphere, temperature or ecology to be similar to those of Earth in order to make it habitable by humans.
“I use the term to describe transformation of a city’s built environment so that it more closely resembles a rural countryside in terms of environmental advantages.”
But the benefits of green roofs aren’t only environmental. Green roofs also provide for a longer roof life and lower roof maintenance costs by protecting the underlying structure.
They provide insulation against street noise – the reasoning behind the construction of the Netherlands Schiphol Airport green roof. They also improve stormwater management by absorbing rainfall, resulting in lower runoff at peak times, which enables drainage infrastructure to cope without costly upgrades.
Rooftop gardens create social areas for city dwellers and workers and have been shown to speed healing in hospitals. They create habitats for wildlife and provide areas for agricultural production.
The City of Toronto in Canada is promoting the installation of green roofs, following a study into the benefits. The study found:
• A reduction in temperature of 0.5ºC to 2ºC if only 8% of Toronto’s roofs were green;
• Direct energy savings in buildings of $C12 million ($13.5 million) a year due to reduced cooling demand;
• Indirect city-wide energy savings at peak load times of $C80 million a year;
• Reduced levels of C02, NO2, ozone, PM10 and SO2 from the lower urban heat island effect and the trapping of gases and particulates by plants on green roofs;
• A reduction of stormwater flows by 12 million m3 a year, which would mean up to three fewer combined sewer overflow (CSO) events a year, giving Toronto three additional ‘beach open’ days a year, and a total cost saving of $C79 million a year from reduced capital costs for stormwater management, erosion control and CSO.
THE US EXPERIENCE
American landscape architect Jeffrey L Bruce, principal of Jeffrey L Bruce and Company, says stormwater management has been behind the green roof movement in the US.
“Green roofs are linked with the green architecture movement certainly, and there’s an understanding of climate change more recently, but they’ve been driven more by stormwater management.
“Most of the cities’ infrastructure is overtaxed with antiquated combined sewer and storm systems so they’re are facing huge infrastructure investments in order to c
orrect the water quality issues.
“The Environmental Protection Agency is mandating certain targets for clean water in the States, and local governments are concerned about meeting the new standards. So it’s not only climate change that’s been a driving factor, it’s this imminent deadline.”
Bruce’s landscaping firm specialises in high technology design, including green roofs, engineered soils, irrigation engineering, sports pitches and sports fields. It has designed more than 60 green roofs, including the famous Millennium Park Chicago, the first green-roofed rail yard in the world.
“A lot of the gardens we produce are commercial, but a majority of them are institutional – large public facilities, large public spaces – and what we’re seeing in the States is that the public agencies and public land owners are the ones taking the lead and creating these types of facilities.”
Bruce believes that Australia, like the US, will rely on commercial viability to encourage the rest of the market.
“The obstacle really becomes the initial cost. If you take a broader perspective and look at the public and private benefit side and life-cycle cost then it’s a no brainer.
“What’s going to drive the private industry side is verifiable data that if I have a green roof on my structure I can lease my roof for this much because most commercial developments are driven ultimately by the rental or sales.
“What you tend to find out is the floor area ratio of the structure versus the roof tends to distribute the cost, so it’s more expensive in single-storey ‘big box’ developments because you’re not distributing the cost of the green roof across 30 storeys of condos, so the cost per square foot is borne.
“For condo developments and apartment complexes they’re starting to get it in the States – starting to understand if we create a nice amenity people will pay more rent for it. We’re going to have a much more difficult time penetrating small commercial structures.”
BUSINESS BACK HOME
A Brisbane real estate valuer specialising in green roofs, John Stephens, says green roof valuations for rental and capital appreciation yield a premium of 10-15%.
Wilson of GRHAC says Australian municipalities could take a lead from cities overseas, where buildings with green roofs have, for example, extra car park spaces approved.
“Some municipal authorities also now offer fast tracking of building designs that have green roofs – thus reducing the original cost of the building and adding to its value.”
He says the commercial viability of green roofs extends past the development industry to business opportunities in other industries, such as rooftop agriculture and native plant exportation.
“It is demonstrably good for our fiscal economy. Australian built-environment professionals can team with Australian primary producers for new business opportunities. Both can specialise in the nascent urban greenery market.
“Many Australian plants from coastlines and inland areas are suited to green roofs and green walls that require low-maintenance urban vegetation tolerant of heat and cold, and drought and wind. These native plants represent a big new regional business opportunity in Australia as green roof retrofits and new designs expand. A global export market is expected to develop.
“A new horticultural industry in prospect for Australia well deserves government analysis and support – as an important economic offset to whatever business advantage may be lost in reduced coal use.
“A similar economic offset is possible in new careers and new business for urban planners, architects, landscape architects, horticultural and landscape contractors, builders, roofers, developers and building owners. New careers will also develop in built-environment regulation, research and academia.” 
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