Viability of Recycled and Waste Materials As Green Roof Substrates

Abstract

The use of engineered Green Roofs on both new and existing buildings has been steadily gaining popularity in many cities around the United States. Green Roofs potentially offer many environmental benefits including: rain water retention to reduce flooding and combined sewer overflows, filtering pollutants from air and rooftop runoff, lowering ambient carbon dioxide levels, reducing the heat island effect, improving building insulation, and attenuating urban noise. Given their growing popularity, there is opportunity to realize additional benefits by using recycled and waste materials in Green Roof substrates. More specifically, the potential to reduce urban waste streams, reduce the overall cost of Green Roof construction, improve performance compared to commercially available media, lower Green Roof design loads, and earn additional LEED construction points. There is, however, a need to quantify and compare the benefits of green roofs constructed from commercially available media with those constructed from recycled media. In this study, recycled substrates were created from waste drywall, concrete, roof shingles, glass, and lumber cuttings by processing these materials into aggregate form. The intrinsic properties of the commercial and recycled substrates, such as unit weight, water retention, leachability and grain size distribution were then analyzed to predict the viability of each material to improve green roof performance. Finally, the results were compared to recommended bulk property values to identify substrates to be field tested.