Fabricio Bianchini and Kasun Hewage
green roofs, urban water retention, lifecycle, environmental benefits
Green roofs are built with different layers and variable thicknesses depending on the roof type and/or weather conditions. Basic layers, from bottom to top, of green roof systems usually consists of a root barrier, drainage, filter, growing medium, and vegetation layer. Environmental and operational benefits of green roofs are many. Vegetative roofs must be installed on existing structures to maximize their potential environmental benefits; however, their main disadvantages are cost and weight. New technology enabled the use of light materials such as: low density polyethylene and polypropylene (polymers) to promote their installation. Nevertheless, lifecycle analyses demonstrate that more sustainable products must replace current green roof materials. This paper evaluates water retention performance of green roofs built with construction and demolition (C&D) waste. Storm water retention of C&D based green roofs were assessed experimentally by comparing the rainwater retained in C&D based green roofs with standard green roofs, under the same environmental conditions. Additionally, basic water quality tests were conducted to compare the runoff quality with the rainwater quality. Results show that C&D waste, compared to plastics, reduces the water retention performance. However, the runoff water quality is better in terms of electro-conductivity, pH, and turbidity. The benefits of installing vegetative roofs in the regions with high rainfall and flood risk are potentially enormous.
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