Green Roof Thermal and Stormwater Performance Comparisons Between Native and Industry-Standard Plant Species

There is a demand to use native species on green roofs in North America. However, research is needed to determine which native species are suitable for the green roof environment and how these species impact the ecosystem services attributed to the green roof. This study compared the thermal performance and stormwater mitigation services provided by species native to Nova Scotia, Canada, and those commonly used by the green roof industry. The study was conducted on two extensive green roofs using a vegetated mat system. The native and Sedum treatments resulted in similar substrate temperatures and stormwater retention for the majority of the study period. Additionally, the green roof treatments performed significantly better than the conventional roof treatment for the majority of the study period. However, at both study sites the Sedum treatment recorded significantly lower average substrate temperatures for the summer of 2014. Since canopy density did not play a significant role in these findings, these results are most likely due to differences in species composition. For stormwater retention, no significant differences were detected between the Sedum and native treatments for the entire study period. This is particularly interesting because the substrate cover in the native treatment was significantly lower than in the Sedum treatment for the entire study period. It is possible that, as the cover of native species increases, the water retention in these modules will also increase. This study demonstrates that these native species are a viable option for green roofs in a maritime climate