Rooftop Garden and Water-Permeable Pavement Mitigate Heat Island Effect

Obayashi Corporation, a major Japanese construction company, announced on October 10, 2003, that, based on measurements and data analyses carried out by the company, rooftop gardens and water-permeable pavements have a cooling effect on the heat island phenomenon common to major urban areas. Obayashi conducted the study at Namba Parks, a new shopping mall in Osaka City that it built and opened on October 7.

The rooftop garden at Namba Parks is about 8,000 square meters in area and contains about 40,000 plants, including 35 kinds of trees and 200 kinds of flowers. It is one of the largest rooftop gardens in Japan.

Temperature measurements were conducted over three days starting on August 20, 2003. The average surface temperature of the green areas in the rooftop garden at noon was 34 degrees Celsius, with a low of 32.3 degrees Celsius. Compared to rooftop parking lots and the asphalt surfaces of nearby highways, a cooling effect of 17 degrees Celsius on average was observed during peak hours. It was also recognized that the amount of the heat transmitted from the green areas on the rooftop to the inside of the building was only one tenth of that from non-green areas.

The water-permeable pavement system is a state-of-the-art technology developed by Obayashi, which got the idea from the traditional Japanese cooling method of sprinkling water on streets. In this system, rainwater that has seeped through the road surface is stored under the pavement and percolates back through the pavement by capillary action, cooling down the street by releasing heat through water vaporization. During daytime in summer, the surface temperature of water-permeable pavements is as much as 25 degrees Celsius lower than asphalt surfaces, and reflected heat is reduced by 20 to 40 percent.The infiltration of water through the pavement mitigates both the heat and the glare.




Posted: 2003/12/25 09:13:49 PM
Japanese version