Green skins

28 Jun

June 21, 2008

Garden roofs and leafy walls could be crucial steps in the fight against global warming, writes Greg Callaghan.

Take one glance at images of the eye-catching ACROS building in Fukuoka City, Japan, and you’ll have no trouble believing that a 21st-century office tower can be eco-friendly. Yes, it boasts a host of energy-saving features ranging from densely insulated walls to compact fluorescent globes, but this is a building that wears Mother Nature’s theme colour on its sleeve – or more specifically, on its back. On the street entrance side, it looks like an ordinary office building, all steel and shimmering glass; at its rear it’s a 15-storey cascade of lush garden terraces pouring down to a park: a green, living oasis in a sea of dead, grey concrete.

Green is the right word to describe the flora-embracing features now being incorporated into new and old buildings across the US, Europe and parts of Asia. We’re talking garden rooftops, multi-levelled terraced gardens, lush foliage draping exterior walls and vast, internal, Babylonian hanging gardens. “Living” buildings, some call them – and they’ve been credited with emitting far fewer greenhouse gases than their vegetation-free counterparts, even the most energy-efficient ones.

Not only do their green-clad exteriors freshen the surrounding air, insulate against heat and cold, and reduce flash flooding in the streets by soaking up rainfall, but they’ve also been found to better absorb street and plane noise, which magnifies as it bounces off hard metal roofs and concrete exteriors. Not to forget their warm and fuzzy aspect: built-in gardens create a soothing refuge for a building’s residents and workers, taking the pressure off public parks. All of which explains why some of the world’s leading architects are designing buildings that can only be described as nature-loving, with built-in structures to support living walls and rooftop habitats that can range from grasslands to birch forests, which in turn can support bird and insect life.

Some of these green marvels, such as the ACROS building, have become landmarks in their cities. The exterior of fashion designer Ann Demeulemeester’s new store in Seoul, South Korea, is carpeted in fine Japanese spurge, which also blankets the interior stairwell walls; the Quai Branly Museum in Paris has a hydroponic garden climbing its walls; the School of Art, Design and Media in Singapore is topped by an undulating, grassy roof, similar to Canberra’s Parliament House; and Chicago’s City Hall boasts one of the largest rooftop gardens in the world.

If all goes to plan, Sydney will have its own verdant towers, too – by no lesser names than architectural superstars Jean Nouvel, designer of Quai Branly Museum in Paris, and Norman Foster, creator of London’s iconic “Gherkin”, the Swiss Re Building. The former Carlton & United Brewery on Broadway, a sprawling 6ha site just south of the CBD, is to be redeveloped as a residential and commercial corridor linking the 19th century, terraced suburb of Chippendale with the glass-and-cement fortress of the University of Technology, the centrepiece being two green towers (see below).

Thanks to new technologies and growing green awareness, city councils worldwide are waking up to the advantage of giving buildings a living skin. In parts of Germany, new buildings must now have garden roofs by law; earlier this year, London’s city council released a statement encouraging developers and building owners to install green roofs on their buildings; Chicago, a pioneer in green roof policy, has more skyscraper gardens than any city in the world; and Tokyo recently introduced policies requiring green roofs to be installed on 20 per cent of all flat surfaces. Not to be outdone, the City of Sydney Council announced last August that it would explore planning guidelines to promote rooftop plantings across the CBD.

Why the sudden interest? Because a string of recent studies has revealed the startling energy savings that can be made by inviting Mother Nature into building design. On average, buildings devour at least 40 per cent of a city’s energy – and up to 70 per cent in mature cities such as London or Sydney – and these figures will almost certainly climb in the decades to come as more and more rural space worldwide succumbs to the relentless march of urban sprawl.

Traditional rooftops, covered in black asphalt, are heat-absorbing surfaces that en masse create the “urban heat island effect”, in which city areas tend to be two or three degrees hotter than the surrounding countryside. On a 23ºC degree day, the temperature on a black tar roof can rise to a blinding 45ºC, while a green roof will maintain the ambient temperature, according to studies in the US. It’s been estimated that if just 20 per cent of the rooftops in Manhattan had green roofs, the temperature of the island could be reduced by two degrees on a summer’s day. A report in BioScience estimates that green roofs can reduce air conditioning costs by 25 per cent and electricity by up to 50 per cent.

So dramatic are the energy savings and environmental benefits of greening a building, says Jim Osborne, NSW representative for Green Roofs Australia, that an increasing number of architects and developers see it as a golden opportunity. “For a dollar result, it makes perfect sense,” Osborne says flatly. “It’s also the lowest-hanging fruit – something we can do now to combat the urban heat island effect and global warming.”

This week Green Roofs Australia – a not-for-profit group – held a conference in Brisbane, investigating new technologies and methods for greening our buildings, and ways to spread the word. “There is a coming together on the issue that just hasn’t been there before,” Osborne enthuses.

But if vegetation-clad buildings are such great machines for delivering fresh air and sunlight to the people who work and live inside them, why haven’t more city councils given them the er, green light? Simple, says Osborne. Most Australian cities haven’t had a mechanism in place to approve them. Proposals for green roofs and vertical gardens have sometimes been rejected by sceptical city councils because sufficient details haven’t been provided on how these gardens would be maintained. And until the past three or four years, their environmental benefits haven’t been recognised. What we need, says Osborne, is a single Australian standard for the wholesale uptake of green roofs.

*   *   *

Green roofs have been around for some time, of course, but they’ve tended to be restricted to small plants, flower beds and grasses because of their shorter root systems and easier drainage. But with today’s advanced filter membranes, waterproof coatings and root barriers, it’s now possible to plant bigger trees and shrubs, and to do so en masse. “Green plumbing” – rooftop water tanks and grey water systems for irrigating plants, powered by solar technology – means rooftop and vertical gardens can be energy self-sufficient. The best of these never need to be watered: rainwater is harvested from the rooftop and pumped to the plants with the energy created by solar cells, which can now be used to heat or cool a building.

An average 1000mm annual rainfall is enough to support a self-sufficient rooftop garden, notes Osborne. Choosing the right plant palettes for the local climate should mean the gardens will thrive with little maintenance, he says. Deciduous plants are ideal because they absorb most of the sunlight and keep the roof cool in summer but in winter drop their leaves, allowing the dark soil to absorb sunlight. Contrary to popular wisdom, wall climbers, with the right surface treatment, can protect masonry against driving rain, hail and scorching heat.

Elevated gardens are still far more complicated to design and install, however, than those on the ground. Retrofitting older buildings for a rooftop garden can be challenging, because of the weight of the soil and plants. “Substantial reinforcement of an existing structure or inclusion of extra building structural support may be required,” concedes Osborne.

The prime prerequisite for a green roof treatment is, of course, a flat surface, so not all city buildings are suitable. It’s been estimated that a third of rooftops in London could be greened, and the figure is likely to be much higher in Australia because we have far fewer 19th century pitched roofs.

While the initial costs of installing a green roof can be high, the energy savings are likely to pay for the investment within a few years, says Osborne. And what price can you put on giving yourself a peaceful patch? 

Senior editor Greg Callaghan’s previous story was “The shape we’re in” (April 5-6), about changing body sizes in Australia.

Leading lights on Broadway

On a former brewery site in Sydney’s Broadway – a prime parcel of land on the CBD’s southern fringe – plans are afoot for Australia’s first six-star green precinct, the centrepiece of which will be two “green” towers designed by “starchitects” Jean Nouvel, winner of the 2008 Pritzker Architecture Prize (the highest honour of his profession) and world-renowned British architect Norman Foster.

Nouvel has created an iridescent residential tower whose terraced, hanging gardens seem to defy gravity; Foster has mature plants sprouting from every level of his light-filled structure, which embraces and soars above a 1930s hotel. Other buildings on the $2 billion building site, designed by Australian master architect Richard Johnson, have the natural world integrated into them and centre on a large central park. The precinct will have its own waste-water-recycling plant, will generate much of its own electricity, and will have 90 per cent of its parking underground.

Climate and environmental considerations should be the starting point for any architect designing a building, says Nouvel, on the phone from Paris. “The sun, the wind, heat and cold – it should be part of the strategy for defining a building,” the 62-year-old explains. Buildings, he says, don’t just have to be kind to nature – they can learn lessons from it and imitate it.

While some architects aim for a stand-out building, Nouvel says the designs of his buildings are inseparable from their settings, so that many of the heritage buildings on the site will be retained and restored. “It’s important for a building to be sympathetic to its historical context,” he says. “And to improve on it.”

But designing a building is only half the battle. The real struggle is getting the thing built. Dr Stanley Quek, CEO of Frasers Property group, which is developing the site, hopes that construction will begin next year. Says Quek: “We’re aiming to create the most environmentally sustainable residential and commercial precinct in Australia.”

Greg Callaghan


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