Green roofs in building retrofits: outdoor microclimate benefits and energy savings

The impact of green roof retrofits on the local microclimate and energy consumption of a building is investigated. This research is based on a case study of Kerr Hall located on the Ryerson University campus in Toronto. The software ENVI-met is used to simulate the microclimate while EnergyPlus is used for the building energy analysis. Results indicate that increasing the leaf area index (LAI) of the green roof leads to increased cooling effect up to 0.4 degrees C during the day at pedestrian-level; however, more significant cooling is attained at the rooftop-level. The addition of the green roof reduced both the heating and cooling demands and improved indoor comfort levels. Energy demand reductions up to 3% were obtained with the green roof retrofits with the biggest contribution form from reduction in heating on the top floor. Increasing the soil depth had a larger impact on the energy consumption compared to increasing the LAI.