Thermal Properties of Green Roofs in Cold Climates

Abstract

Green roofs have, in the past 15 years or so, gained increasing acceptance as a means of replacing or offsetting the lost of green space due to urban development and urban sprawl. Green roof systems can provide numerous potential benefits, both public and private, including improved control of a building’s internal temperatures with reduced power use. The effectiveness of Green roofs at decreasing energy use in buildings in warm climates is well known. However, their thermal performance in cold climate conditions is not well known, but is of particular interest in regions such as in Eastern Ontario where Green roofs are rapidly gaining popularity. This thesis presents an initial step in understanding the thermal behaviour of currently used Green roof systems in cold climate conditions, and quantifying the thermal benefits, if any, to be gained from the installation of these systems in cold regions as compared against a typical conventional roofing system. A review of available literature is presented which discusses the various benefits of Green roofs. A novel hot box has been designed and constructed, and thermal testing of two Green roofs and a conventional flat roof using the new apparatus are presented and discussed. The data are used to estimate the potential energy savings that might be expected with the installation of a Green roof (such as those tested) on a flat roofed commercial building in the Kingston area. The data suggest that Green roofs may provide a marginal (10% to 24%) thermal benefit as compared with a conventional flat roof under cold climate conditions. This benefit could translate into a $0.09 savings per square metre of roof area in total heat energy costs on an annual basis. Recommendations for future work in this research area are provided.