Performance of green roof installed on highly insulated roof deck and the plants’ effect: An experimental study

Extensive green roof system is widely used due to its lightweight, thin growing media, limited or no maintenance, low cost, and high potential application for use over the new or existing lightweight structures. This study is focused on the energy performance and rainwater retention performance of extensive green roofs when coupled with highly insulated roof deck. In this experimental study, three roof systems: conventional roof (CR) and two extensive green roofs with plants (GR) and with no plants (GM) are constructed, instrumented and their responses to real environmental conditions are monitored for over a year and analyzed. The experimental results suggest that during wet period, the rainwater retention potential of green roof is only about 21%, while in the summer the rainwater retention capacity increases as high as 100%. Plants play an important role in rainwater interception, growing media wetness, rain runoff and the green roof's thermal performance by modifying short- and long-wave radiation and as well as convective heat exchanges. Installation of green roofs on highly insulated roof decks yields a mixed performance in a mild and wet climate. The heat loss through the green roof during the heating months is about 2% higher than a similar roof without green roof. Whereas during the cooling months the green roof is able to reduce the heat gain by 66%. This substantial heat gain reduction can help to reduce overheating problems in highly insulated buildings.