Thermal Performance of Extensive Green Roofs in Cold Climates

Green roof is a specialized roofing system that supports vegetation growth on rooftops. This technology is rapidly gaining popularity in North America as a sustainable design option. Green roofs offer multiple benefits to urban areas such as reduction of heating/cooling needs for the building, urban heat island and stormwater runoff for the region. In this study, the performance of two extensive green roofs located in the City of Toronto, Ontario, Canada was monitored. The green roofs varied in system components, types and depths of growing medium, vegetation coverage and types of roofing systems. The green roofs were instrumented with sensor networks to provide thermal performance data. Observations from the first year of monitoring showed that the green roofs reduced the heat flow through the roofs, thus lowering the buildings’ heating/cooling energy demand, independent of the roofing systems the green roofs were installed on. Although the plant coverage was relatively low in the first year, the green roofs reduced the annual heat flow through the roofs and they were more effective in the summer than in the winter. Energy efficiency varied slightly with growing medium depth and system design.