A multi-year comparative analysis of green and conventional roof thermal performance under temperate climate conditions

Research suggests that—relative to conventional roofs—green roofs can significantly reduce rooftop heat exchange in moderate climates; however, limited research exists on the performance of green roofs in colder climates. This paper analyzes the comparative performance of two side-by-side roof assemblies: a conventional roof and a green roof located in the temperate climate of Ottawa, Canada. Using two years' worth of temperature and solar radiation data, we analyze variations in the incremental thermal benefit of the green roof relative to the conventional roof. We discuss factors contributing to these variations, such as precipitation and ambient temperature. Our results indicate that the green roof under investigation reduced thermal transmittance by 31.5% on average across two years. Although the percent benefits were much higher during the summer months, reductions in thermal transmittance were consistently above 7.7% throughout both years, indicating green roofs may be an appropriate alternative to conventional roofs in climates with hot, humid summers and cold, snowy winters.