A rooftop garden in central Tokyo. (Kajima Corp.) ROOFTOP GREENERY: Growing Plants on Buildings to Absorb Heat October 4, 2001 Many of Japan's leading general contractors are putting efforts into the development and sale of products related to rooftop greenery, which involves planting trees, flowers, and other plants on top of condominium and other buildings so as to absorb heat. And some home furnishing companies are selling rooftop-greenery systems for individual homes. It is hoped that rooftop greenery will lessen the "heat-island" effect, cut air-conditioning costs, and reduce noise pollution. The national and local governments are beginning to take up the challenge of encouraging the spread of this technology. The Tokyo metropolitan government passed a law requiring new buildings to make use of rooftop greenery beginning in April 2001, and the Ministry of Land, Infrastructure, and Transport has proposed fixed-asset tax breaks for greenery equipment. As demand seems likely to grow, competition looks set to heat up. A Growing Business Obayashi Corp., a large general contractor, has developed a thin, lightweight system that involves laying a five-centimeter-thick sheet across a rooftop. The sheet, which serves as a kind of base from which plants can be grown, costs only about 10,000 yen (about 83 U.S. dollars at 120 yen to the dollar) per square meter (10.76 square feet), including both materials and the cost of installation. This is only a third of the cost of similar services offered by competitors. Kajima Corp., another general contractor, in June 2001 established a model garden of rooftop greenery on the top of its building in central Tokyo using its own lightweight soil. This is not merely a rooftop greenery system; in addition to growing plants in greenery panels made of artificial, lightweight soil that cover the walls, an aquatic environment replete with butterflies and water striders has been created to form a biotope. The move toward rooftop greenery is not limited to businesses and high-rise condominium buildings. Home manufacturers and others have begun selling products one after another that will allow individual home owners to convert part of their roof into a flower garden. The biggest technical obstacle involved in rooftop greenery is the limit to the amount of weight that a roof can take. Since the soil has to be light enough that the roof can support it but heavy enough that it does not blow away in the wind, the cost is rather high. This has led many companies to engage in cost-cutting competition. In order for rooftop greenery to spread, lower installation costs, lighter weight, and easy maintenance are essential. Benefits of Rooftop Greenery It is hoped that rooftop greenery will provide a number of benefits. As Tokyo is covered with concrete and asphalt, the ground temperature can become quite extreme in what is known as the heat-island phenomenon. This effect, however, may be lessened by the leaves of plants, which release water vapor and cool the surrounding area.   Your Name Send this article to a friend According to the Organization for Landscape and Urban Greenery Technology Development, if half of Tokyo's buildings covered their roofs with plants, high temperatures would fall by 0.84 degrees Celsius (1.5 degrees Fahrenheit) during the summer, resulting in an average daily savings of 110 million yen (916,666 dollars) on air-conditioning costs. It would also help clean the air, reduce noise pollution, protect buildings, and improve the view. Government Backing In April 2001 Tokyo became the first metropolitan area in the nation to require new buildings to place greenery on 20% of the available space on rooftops. The Ministry of Land, Infrastructure, and Transport has put forth a plan to reduce fixed-asset taxes on greenery equipment. Local governments have gotten into the act as well, with Osaka, Sendai, and Kanazawa introducing systems that provide financial assistance for rooftop greenery. Gardening is something that has long been a part of Japanese life; people enjoy growing plants in their gardens, on verandas, and on rooftops. Now the Japanese love of plants seems ready to go one step further. It is hoped that the spread of rooftop greenery to buildings and ordinary homes will not only reduce the heat-island effect but also play a role in preventing global warming. Copyright (c) 2001 Japan Information Network. Edited by Japan Echo Inc. based on domestic Japanese news sources. Articles presented here are offered for reference purposes and do not necessarily represent the policy or views of the Japanese Government.