Gardens: Facing up to vertical gardening

Jessop Gardeners have long "trained" plants to grow up and along walls, but architects and structural engineers have tended to view plants as a danger to design and even to structural stability. That perception is changing with improved technology, however, and vertical gardens have become fashionable since French scientist and botanist Patrick Blanc showed their possibilities with the Musée du Quai Branly, which was designed by Jean Nouvel and opened in Paris in 2006.

Now, buildings coated in hanging gardens are popping up around the world.

Plant roots can exploit even the tiniest crack in a building and over time cause tremendous damage, but Mr Blanc devised a system in the 1990s that helps prevent such damage. A heavy-duty PVC sheet is riveted to a building's metal frame, adding rigidity to the structure and making it waterproof, while a felt layer made of polyamide is fixed to the PVC and acts as a water distributor, with the roots growing on the felt, without soil.

His system has been copied and refined, but its use has been mainly aesthetic, although some supporters claim it can have such environmental benefits as improving the quality of the ambient air.

A new project is hoping to show that, combined with a suitable insulation system, greenery on walls can also help reduce the thermal effects of the sun.

The Singapore FreePort, a high-security warehouse for collectibles – including paintings, gold, cigars and wines – has been designed with a thick thermal insulation envelope, the performance of which is enhanced by two vegetation-covered facades, protected from the tropical sun by an aluminum and stainless steel mesh.

Carmelo Stendardo, of Atelier d'Architecture 3BM3 in Switzerland, says that rather than using Mr Blanc's style of independent, prefabricated panels, he has used "a rather traditional system of tropical creepers planted in linear vats at the base of the building, which will gradually colonise the facades, which are covered with a system of felt-cloth and metallic wire netting".

He said that using wire mesh, which shades the plants, was a real innovation.

"There is an aesthetic aim, but the use of the plants combined with the insulation and the mesh wire can also have a very functional aspect," said Olivier Andres, director of Rigot & Rieben Engineering in Switzerland, which was involved in the project.

Shielding a building with a layer of energy-absorbing organic matter could lower internal temperatures by about 3.5C, compared with a building protected by 4cm of conventional insulation, he said.

For the FreePort building, the landscape architect Blaise Bourgeois of Oxalis, a Swiss business, chose creepers from the araceae family, such as climbing philodendron, which bond themselves through their air roots, and climbers, such as thunbergia and strongylodon, that grow much faster.

More than a dozen species were used, some imported from as far away as Australia and Europe.

"Within a year, the plants should cover half to two-thirds of the building," Mr Bourgeois said.

Choosing the right plants to go on a vertical wall is complicated; in particular, they need to require the same amount of watering, Mr Bourgeois said. Using climbing plants, he said, reduced both maintenance and the number of plants needed – only 400, compared with the thousands used on Mr Blanc's projects.

"Here, we're counting on self-sufficient types of plants, because climbing plants are kinds of invaders capable of finding their way alone on the building," he said. "We also reduce the risk of having lots of plants dying if there were a lack of watering by accident."

Mr Stendardo said he had dreamed of covering the entire building, including the roof, with vegetation, but had to scale back his ambitions because of the costs involved. The green wall added 20 to 30 per cent to the cost of the two facades, he said, although that should be recouped quickly in energy savings.

While vegetation-covered walls may need little gardening attention in a tropical, humid climate, they may not work in more temperate climates, said Vladimir Sitta, an architect with Terragram, an Australian design practice that has worked on a number of urban landscapes and gardens internationally.

Vertical gardens can be likened to patients on life support, he said: switch off the transfusion system, and they will probably die.

"They need high maintenance to look like green eye candies. To me, they are nice gestures, but self-supporting micro-ecologies they are not," Mr Sitta said, pointing to the example of a four-year-old "living wall" that was part of Paradise Park, a children's centre in Holloway, in northern London, where the plants withered and died last year after an irrigation pump broke down. The cost of replanting the wall has been put at 130,000.

"The visual seductiveness of those walls has a number of benefits – it made many people think how ecologically inert our cities have become, and architects are experiencing really seismic shifts in their thinking about building envelopes," Mr Sitta said. But he also sounded a note of caution.

"I maintain my reservations despite my decades of advocacy to change," he said. "We have to develop building materials that maintain human comfort and invite more spontaneous colonisation by plants. Such materials already exist – for example, porous ceramics that look like a sponge. It's a strong material with myriad of holes that could become host to plant life."

For now, those materials are prohibitively expensive, like anything new, he said. But costs could be reduced by precultivating large tiles for installation. "It could spawn a whole new industry."

The New York Times

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• This article was first published in The Scotsman on Saturday, June 12, 2010