Developing Australian green roofs: overview of a 5-year research program

Abstract

Green or vegetated roofs are increasingly built in cities to provide multiple environmental and social benefits and are an emerging horticultural industry in Australia. Since 2008, researchers at the University of Melbourne s Burnley Campus have undertaken transdiciplinary research developing and evaluating green roofs for southern Australian conditions which are characterised by hot, dry summers. We have quantified plant performance through experiments on roofs and in controlled environments, using both Australian native and exotic species, to identify plant physiological and morphological traits that will improve green roof performance. We have developed lightweight mineral substrates based on scoria, bottom-ash from coal fired power stations and crushed roof tiles and evaluated water retention additives to improve water holding capacity and plant survival. Hydrology studies have found that 10-cm deep green roofs with scoria substrate can reduce stormwater runoff in Melbourne by 43-88%, depending on season and plant species. We found that a 12.5-cm deep green roof reduces building energy use by 38% in summer. Environmental psychology research demonstrates that people prefer green roofs with flowering meadow like vegetation and that viewing this type of green roof improves concentration and improves work performance. Our results have been embraced by the Australian green roof industry, resulting in construction of green roofs with our best performing substrates and plants and the development of science-based guidelines for future green roof projects.