| Abstract | Rooftop gardens or green roofs have the potential to reduce urban heat island and storm water runoff. They can also increase membrane durability, provide green space in urban area, and improve property value. Although green roofs represent an inexpensive adaptation strategy for urban area, technical information on the benefits and durability, in a Canadian context, is not available. To address these issues, the National Research Council of Canada (NRC), in collaboration with members of the North American roofing industry, has initiated a research project in 2000 to provide such information. The main objective of this study is to evaluate the engineering performance of green roofs through field study. NRC has constructed an experimental facility, the Field Roof Facility (FRF), in its Ottawa campus in 2000. This provided an experimental roof area of about 72 m2 (800 ft2). The roof is divided in two equal areas by a 1-m (3-ft) median divider: on one a generic green roof was installed and on the other a conventional roofing assembly with modified bituminous membrane was installed as a reference roof. Both roof sections were instrumented to monitor temperature profile, heat flow, solar reflectance, relative humidity, soil moisture content and storm water runoff. This setup allows direct comparison of the performance and benefits of the Green Roof and the Reference Roof. Observations from the FRF showed that a generic extensive green roof with 150 mm (6 in.) of growing medium could reduce the temperature and the daily temperature fluctuation experienced by the roof membrane significantly in the warmer months. While the exposed roof membrane on the Reference Roof was recorded to reach over 70°C (158°F) in the summer, the membrane underneath the Green Roof reached about 30°C (86°F). In spring and summer, the median daily temperature fluctuation of the membrane was reduced from 42-47°C (76-85°F) on the Reference Roof to 5-7°C (9-11°F) under the Green Roof. The Green Roof also significantly moderated the heat flow through the roofing system and reduced the average daily energy demand for space conditioning due to the heat flow through the roof in the summer by more than 75%. The Green Roof was shown to delay stormwater runoff and reduce peak runoff rate and volume. It retained 245 mm (9.64 in.) out of the 450 mm (17.72 in.) of rain fell during April to September 2002 - a reduction of 54%. |
|---|
