STORMWATER MITIGATION AND SURFACE TEMPERATURE REDUCTION BY GREEN ROOFS

Abstract

Green roofs on small 1.8 by 2.4 m buildings consisting of a conventional flat roof covering, a root barrier, a 12 mmthick Enka drainage layer, 89 mm of growth medium, 25 mm of porous expanded polypropylene (PEPP), and Sedum spuriumplanted 76 mm on center were evaluated to determine their potential to reduce stormwater impacts and roof surfacetemperatures. Hydrology data were collected from three replicate buildings with experimental green roofs, and roof surfacetemperatures were collected from both green and conventional roofs, each with a 1:12 slope. The green roof media had anaverage porosity of 55 m3 m-3 and a field capacity of 34 m3 m-3. Rain and roof runoff data collected from seven rains duringOctober and November 2002 showed that the green roofs delayed the start of runoff an average of 5.7 h. The green roofsretained an average of 45% (range 19% to 98%) of the rain from the seven storms evaluated and delayed the peak runoff by2 h. Roof temperature data collected between April 2002 and February 2003 showed that the green roof maximum surfacetemperatures averaged 6C higher in the winter and more than 19C lower in the summer. The differences between theaverage maximum diurnal temperature change at the roof surface averaged 19C during the cooling season (August andSeptember) and 8C during the heating season (October to February).