UCLA

The use of vegetated roofs (green roofs) is a common method for combatting the urban heat island effect and heat-related health consequences. The performance of green roofs depends on the type and composition of its various components, including plants, substrate, insulation, drainage, or other roof layers, as well as climate. While some studies have looked at vegetation’s functional properties in determining thermal effects, none have occurred in Southern California. Because green roof performance is highly dependent on climate, this knowledge gap stands in the way of providing the area with optimally performing designs. This study addressed this knowledge gap by using vegetated roof simulation cells to examine the impacts of two different plant species on thermal properties of a green roof. The plants were two species in the genus Sedum, which is the most commonly used taxon in green roofs. Nine cells were used, where 3 cells had Sedum acre, 3 cells had Sedum rubrotinctum, and 3 cells had bare substrate only. Ambient, soil level, and interior temperatures were collected at 30-minute intervals during the study period, which lasted from March 4th until April 8th. Temperatures were compared afterwards across treatments and location. Both plant species lowered daily maximum temperatures and temperature ranges. However, Sedum acre was far more effective, lowering mean daily max temperatures and temperature ranges by 1.6 �C and 1.4 �C, respectively. Sedum rubrotinctum lowered both mean daily maximum temperatures and temperature range by 0.5 �C.