Raising the roof

Retrofitting existing buildings with green roofs and living walls is speeding up the pace of improving cities' sustainability, Jez Abbott.

Urban greening: ecologist insists idea of cities festooned in vertical and horizontal greenery is not too far-fetched - image: WOHA/Patrick Bingham-Hall
Urban greening: ecologist insists idea of cities festooned in vertical and horizontal greenery is not too far-fetched - image: WOHA/Patrick Bingham-Hall

Ecologist Gary Grant is waiting for planning permission for a green roof on the Rubens Hotel in Victoria, London. It cannot come a moment too soon. Urban greening is becoming and must be a "cornerstone" of planning given that it can help to ease flooding and heat waves, says Grant, author of Ecosystem Services Come to Town: Greening Cites by Working with Nature. Forget talk about urban food production and city farming that is snatching all the headlines, he says.

"The real excitement and growth is in retrofitting existing buildings with features like green roofs and living walls, and in the greening of the surrounds of buildings with pocket parks and rain gardens. As more of the existing building stock is examined we are coming to realise much, much more can be achieved than we first thought."

He continues: "The key area is retrofitting. With new build anything is possible and the only limitation is your imagination. But new build can only ever form five-to-10 per cent of the city. We have found one-third of buildings in central London could be retrofitted with green roofs and living walls, which is a massive combined area."

Great potential

Yet few clients realise that you can take up paving slabs and weigh down roof insulation with earth and turf, says Grant. Potential is even greater for walls, without the same weight constraints, because you can build a frame in front to take the weight of plants. The idea of cities festooned in vertical and horizontal greenery is not too far-fetched, he insists.

As the options for new build and retrofitting flourish, so the business openings become wider for suppliers and landscape contractors, adds Grant, who has noticed a number of niche start-ups and existing firms making urban greening their core specialism. But be warned, installing a green roof or wall is not like ordering a product such as tiling.

"Now is the time for specialists in different fields to come together to offer a USP, as the technology is moving forward so quickly. You have to understand detailing, microclimates and north and south aspects. There is still a learning curve, but in future people will look at old photos and say: 'How did we manage to live without all this greenery?'"

On learning curves, RHS principal horticultural adviser Leigh Hunt told a PlantNetwork conference in April that sedum, often the first choice for green roofs, may be less effective at cooling than Stachys byzantia, following research with the University of Reading. "We have all been planting sedum roofs but are they better? Is Stachys the next big thing when it comes to making a real environmental difference in cities?" he asks.

As the benefits of green roofs and living walls stack up — reduced heat-island effect, improved storm water and run-off management, better noise insulation, more building energy conservation and improved air quality — so will funding streams. Wildlife charity Buglife recently tapped into landfill-tax money to fund a green roof.

Brownfield officer Clare Dinham says work on the roof on top of the Victoria & Albert Museum is due to start later this spring and was made possible with £20,000 of landfill cash from the Western Riverside Environment Fund, which is a partnership between Western Riverside Waste Authority and Ground­work UK.

Around 150sq m of the existing roof will be transformed into a wild flower meadow to provide food and shelter for wildlife including bees, butterflies and moths. It will feature nectar- and pollen-rich plants, areas of bare ground for invertebrates to bask and burrow as well as piles of deadwood for shelter. The roof will also include wetland features.

Dinham, who is working on the project with Green Roof Consultancy head Dusty Gedge, says organisations such as recycling and resource management company SITA and not-for-profit business conservation group WREN offer grants for green roofs and walls. Buglife is also looking at possible help from university research groups as well as the Heritage and Big Lottery funds.

Paying for retrofitting

Gedge, meanwhile, does not hold out much hope for Government funding streams, but future sources of money could be the utilities. "People like Thames Water need to pay towards retrofitting green infrastructure," he insists. "Most of our cities have antiquated storm water sewers, which fail in flash floods. I reckon within five years utilities will be spending big on retrofitting."

This is starting to happen. Peacehaven boasts the largest grass roof of its kind in Britain, with a sward equivalent to four-and-a-half football pitches on Southern Water's waste water treatment works. Frosts Landscape Construction built this award-winning green roof and won another prize for a living wall for a London hotel (see box).

Last year, Buglife and the Green Roof Consult­ancy, produced the UK's first living-roof guidance report that could prove a valuable reference for start-up operations. Such brainstorming is burgeoning. Also last year, the World Green Roof Congress took place in Copenhagen, which is one of the world's most sustainable cities along with Oslo, Vancouver, Curitiba and San Francisco.

Copenhagen mayor Frank Jensen told the conference that smart cities of tomorrow will be green cities and the world's "mayoral offices understand urban biodiversity and green infrastructure are essential for any city vision". This sentiment is echoed in policy form with a climate change adaptation strategy from London mayor Boris Johnson.

All major new developments in most of central London, the City, parts of Westminster and the inner parts of Camden, Islington, Hackney, Tower Hamlets, Southwark, Lambeth and Kensington and Chelsea are required to have a green roof. Johnson launched his strategy with a starting-point ambition of delivering 100,000sq m of new green roof space in two years.

Such responses to climate change must be immediate, landscape architect Peter Wilder told a recent Ecobuild conference in London. Wilder, a future cities consultant for the Building Research Establishment, is working on the biggest eco city in China and says without living walls, roofs and other green infrastructure, the mounting physical and mental-health problems caused by urbanism will "come back to bite us".

Gedge took up a similar theme three weeks ago at the Hungary Green Roof Association and is to regale the International Green Roof Congress in Hamburg in mid May. International Green Roof Association director Wolfgang Ansel says the 21st century metropolis must balance sustainable growth with climate protection.

"The global trend towards urbanisation continues to accelerate, but the answer is located directly over our heads. Urban roofs are offering huge potential, be it an exclusive rooftop garden, a public park, a rooftop farm, a storm-water management facility or a nature conservation area. There are almost no limitations — the sky is the limit."

 

Green case studies: London, Singapore and Milan

Mint Hotel, London

Frosts Landscape Construction was commissioned to build more than 1,000sq m of green wall extending up to the 11th floor of a new hotel development. It is Europe's largest living green wall and cost £750,000.

The wall for the 583-bedroom Mint Hotel near the Tower of London billows with 184,000 plants and is topped with a 350sq m green roof, making this one of the largest areas of structural landscaping on a UK building. The living wall wraps around the building on all four elevations and in parts extends up to the 11th floor — 35m in height.

Plant modules were grown off site before installation. The green roof is made of sedum and wild flower plugs. Frosts won a BALI principal award for the project in 2011.

Breathing Architecture, Singapore

Newton Suites in Singapore helped architect Wong Mun Summ and his practice WOHA win a green design award last year. The 36-storey high-rise has several passive climate controls, including sun-shading and creeper screens blended into a contemporary architectural form with rooftop planting, "skygardens" and green walls.

Horizontal and vertical surfaces are draped in landscape to "represent a refinement of vertical living in dense metropolitan cities that achieves high quality of life for residents and the neighbourhood," says the practice, adding that its unique tropical building achieves both Singapore's national vision for a green city and an improved living environment for its people.

Bosco Verticale, Milan

Bosco Verticale (vertical forest) is a project for metropolitan reforestation, environmental regeneration and urban biodiversity in one of Italy's most polluted cities.

Two residential towers, each with 900 trees up to 9m tall, shrubs and floral plants, boast an area of greenery equal to 10,000sq m.

Architect Boeri Studio points out that its £56m towers will help to create a microclimate that filters out dust particles, improves humidity, absorbs CO2, produces oxygen and shields against radiation as well as acoustic pollution.

Irrigation will be reliant on the filtering and reuse of the grey water produced by the building. Aeolian and photovoltaic energy systems will work with the microclimate to increase energy self sufficiency.


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