Green roofs for a greener world

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Perhaps we should thank the builders of Babylon. The city’s famous “hanging” gardens, a series of planted and elevated terraces with wells set on a small hill behind a palace, were certainly one of humanity’s first attempts at creating an oasis of green in an urban residential setting.

The Romans followed suit, replacing their private homes with tall apartment buildings as ancient Rome’s population swelled, and, as Seneca describes, installing roof gardens with shrubs, grape arbours, fish ponds and fruit trees planted in boxes of earth.

And the tradition continues today. In London, developer London + Regional Property Fund and architecture company Tasou are creating a collection of four new-build houses and three flats in a gated mews space surrounded by tall buildings; each house will have a large roof terrace with decking, planting and an outdoor shower. In New York, designer Philippe Starck is partnering with Yoo to convert the former headquarters of JP Morgan into a luxury apartment building, complete with “roof park” full of trees and surrounded by a big hedge. And in Tokyo, where the government has made environmentally friendly “green” roofs mandatory for new buildings, architect Akira Yoneda has built Ambi-Flux, a five-storey structure on a site 13ft-wide site, crowned with a sun-filled garden.

Indeed, for aesthetic, ecological and financial reasons, planted roof spaces on top of residential buildings are becoming increasingly common in big cities around the world. For most homeowners, the obvious advantage is the opportunity to have outside space in which to relax. Some visit the spaces to simply, well, smell the roses. Some grow their own vegetables. Others throw parties.

“In central London, a more outdoor lifestyle can be seen in the spread of pavement cafés and restaurants,” says Simon Barry of estate agent Knight Frank. And “with it has come an increased demand for outside space – especially in those designed for the luxury end of the market.”

Roof terraces are also a way for developers and homeowners to command premium prices for their properties. “It instantly lifts the value of the apartment,” says Pierre Wilter of London-based Urban Roof Gardens. “And that can be anything from 10 per cent up to about 35 per cent. So if you’re looking at property prices of £250,000 to £400,000, that’s a big whack on top of that.”

As officials in Tokyo and other cities have recognised, “green” roofs are good for the environment too, naturally cooling the structure below and, like a giant sponge, absorbing excess storm water that can overload drainage systems. They can also help counteract the “urban heat island” effect – whereby a city’s many large surfaces absorb the sun and return heat into the air. A study from Environment Canada and Toronto has suggested that covering just half the city’s roofs with grass and other plants would create reduce its average temperatures by 1° to 2°C.

When it comes to the practicalities of designing a roof garden, one of the main considerations is weight. “If you think about a roof terrace, it’s the wrong thing to put on top of your house because it’s heavy and traps moisture,” Wilter says. But new technologies, from lightweight soils to rubber membrane systems that allow roots through but not water, have been developed in recent years. And architects, professional landscape designers and horticulturalists can help achieve the right balance.

A good example for would-be rooftop vegetable gardeners is the design adopted by New York’s Earth Pledge Foundation for the space on top of its office building. “You can’t grow tomatoes in two inches of soil, so you need to adjust the depths to whatever you want to grow,” says executive director Leslie Hoffman. “We’ve done that in different ways. One part of our roof can support a deeper soil, so there we’re doing tomatoes, peas and herbs and we have planter boxes that are quite deep. Then in the shallow areas, we have lettuces and greens that don’t need much soil and grow fast.”

Climate also needs to be taken into account. Since rooftops tend to be hotter in summer and colder in winter than ground-level spaces, elevated gardens may dry out more quickly and require supplemental watering. Atop tall residential towers, strong winds can also be a problem, so barriers also need to be considered.

Potted plants and container gardening are the easiest way to create high-rise greenery, since they can be filled with whatever soil is appropriate and are often also decorative objects. Designer planters in materials such as bronze, marble, earthenware and wood conjure up anything from a Mediterranean-style terrace to a rustic retreat. However, once full of soil they can be heavy, so attention still needs to be paid to the weight distribution across the roof or terrace. One solution is hydroponics (a technique for growing plants without soil): the tanks, which pump a solution that contains all of the plants’ necessary nutrients through an inert medium such as sand, peat or vermiculite, weigh less than soil-filled planters.

Amir Schlezinger of London-based MyLandscapes says that the top request he gets from clients – particularly wealthy city professionals – is that their roof garden require little maintenance. So he focuses less on horticulture and more on design, considering not only the roof space itself but also what’s around it. “The exciting thing is working with landmarks,” he says. Cleverly designed landscaping can frame an interesting building or appealing vista. It can also remove something ugly from view and shield the space from city noise.


By Mark Ellwood

Like many Manhattanites, prospective residents of Sutton 57, a condominium complex in midtown, will be impressed by the building’s rooftop amenities. But this time, instead of a pool or some artfully arranged plants, the spotlight is on a moon garden.

The concept is simple: every plant or flower here blooms after sundown, glows in the moonlight or is most fragrant in cooler, night air. “New Yorkers work all the time – they’re never home during the day – so why not create an outdoor space they can enjoy at night?” explains Monica Klingenberg, who’s in charge of selling the 38 apartments (priced from $1.5m for a two-bedroom pad). “It’s a place to go in the evening, ready to relax and sit among the flowers and fragrance on a beautiful summer night.”

The gardener tasked with overseeing and maintaining this programme – which cost just $50,000 for developers to add to the plans – picked night-time bloomers such as white liatris, lamb’s ear and white swan coneflowers, all stashed in crescent moon and full moon planters. As a sop to early risers as well as night owls, he added a few classic flowering plants as well as an outdoor rain shower to cool off sunbathers.

But, for Madrid-born publishing exec Julia Caballero, 43, and her husband, the the moon garden was the deal-closer. “Right now, we live in a very nice building, but we cannot really take advantage of the roof at all, even when it’s July 4th,” she explains, citing long office hours. (Caballero also prefers common garden areas so she can delegate the watering.)

The rooftop spaces on most newer buildings, she says, are centered on a pool, which is ideal for drunken, partying twentysomethings, but less so for Caballero’s lifestyle. “This is an elegant feature – I can really see myself having a glass of wine with my husband and reading the paper in the evening up here.”

Cathy Wilkinson Barash, confirmed midnight planter and author of “Evening Gardens”, predicts that suburban backyards could soon morph into moon gardens, too. “The interest in evening gardens with our crazy schedules has become greater and greater,” she explains. “Night is really the only time people have these days to enjoy their gardens, since weekends are devoted to the chore of taking care of them.”

And the idea isn’t as revolutionary as it seems. “It goes back to the Persian gardens of delight, which incorporated very sensual fragrant plants,” says Wilkinson Barash. In the Victorian era, the moon garden was a fad. And “then there’s Vita Sackville-West’s famous white garden – white flowers with silvery leaves.”

For would-be midnight gardeners, she recommends emphasising contrast in plantings, as well as including water features, such as a pond to reflect the moon and attract shy, nocturnal animals. Choose plants pollinated by bats or lunar moths, or even well-known options such as heliotropes, whose vanilla scent is headier and more concentrated at night.

Most importantly, enjoy the time it takes to slow down and enjoy it. “Your eyes need a good 10 minutes to adjust to the darkness so you have to just sit and be quiet for a while,” she sighs.

■ Sutton 57, tel: +1 212-829 0057;

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