There’s a green revolution on high


Rice will be harvested in Tokyo’s Roppongi entertainment district this fall.

And 40 meters above ground at that, from a 130-sq.-meter paddy on top of the Keyakizaka Complex at Roppongi Hills, which opened last month. On Children’s Day, May 5, two kinds of rice were planted there, to be organically grown using rain water from a pond that’s up there, too.

If all goes well, the rooftop harvest will be around 60 kg — though Mori Building Co., the developer of Roppongi Hills, has yet to decide who will finally get to eat the grains.

In fact the paddy is just part of a 1,300-sq.-meter farm garden atop the complex that houses Virgin Cinemas Roppongi Hills, where vegetables, herbs and several kinds of trees are also being grown.

The plan is to create a biotope up there, attracting birds and insects to the center of one of the capital’s most built-up areas. With this aim in view, Roppongi Hills also has English gardens spreading over the rooftops of its residential buildings.

Mori Building has been enthusiastic about planting greenery in its development areas, which also include Ark Hills in Akasaka. But the latest project in Roppongi — like other major developments in the last year, including Caretta Shiodome in Shinbashi and the Marunouchi Building (“Maru Biru”) in front of Tokyo Station — is also in line with a Tokyo Metropolitan Government ordinance issued in 2001. This obligates builders of structures of more than 1,000 sq. meters in area to crown 20 percent of their roof area with vegetation, and to have greenery occupying at least 20 percent of its non-building area.

The measure is not only an effort to create pleasant green spaces within the city. It also aims to address environmental problems, including counteracting the so-called heat-island phenomenon — the localized warming caused by the high density of heat-retaining concrete structures in cities, as well as the human activity concentrated there. Planting vegetation on rooftops helps to insulate buildings from heating up in summer, which can save energy taken to cool them with air conditioning.

The move is expanding to existing buildings. In fact, some of the city’s 23 wards — including Shibuya, Shinagawa and Shinjuku — have turned the roofs of their own ward offices into gardens to set an example, and also provide information to building owners. They demonstrate what kinds of plants, vegetables or herbs can be planted and grown, as well as the varieties of earth and containers that are suitable for rooftop use.

Similarly, Bunkyo Ward, in cooperation with firms specializing in equipment for rooftop greening, invited the owners of buildings around its ward office to join an initiative to plant vegetation on their roofs. The project was completed last month, and the results are clear to see on the tops of 13 buildings visible from the public observation areas on the 25th floor of the ward building.

Shukichi Ishii, secretary general of the Sky Front Forum, a nonprofit organization which researches and promotes the utilization of urban rooftops, explained that such planting is possible at any height. He noted, however, that there are important differences between making a garden on the ground and in the sky. “Existing roofs have a limit to the weight they can hold, and the wind could blow the earth away or be harsh on some plants,” he said. Hence such factors must be carefully consulted before embarking on a rooftop planting project.

But just installing vegetation on the roof, however laudable, is not the end of the project. “Whether the owners of the gardens can continue to manage and take care of them is the key part of the challenge,” Ishii pointed out. “Just creating greenery on the rooftop is only the beginning of what it’s all about.”