Mandatory or voluntary approaches to green roof implementation: a comparative study among some global cities

Green roofs can deliver multiple environmental and social benefits by reducing the urban heat island effect, reducing building energy use and greenhouse gas emissions, improving air quality, providing habitat for biodiversity and access to the biophilia effect. Green roofs provide these benefits to differing degrees in different climate zones globally. Despite known benefits, uptake of green roofs has been slow. Different cities, globally, adopt various policies and programmes to increase their green roofs; the question is which approach is best? This research used an in-depth review, site visits and qualitative methods, to determine whether mandatory or voluntary approaches produced greater uptake. Green roof policies and practices from selected global cities, London, Toronto, Singapore, Rotterdam and Stockholm, Sydney and Melbourne were examined. Singapore’s voluntary approach led to the greater uptake of green roofs. The mandatory approach taken by Toronto, with financial grants provided meaningful outcomes. London and Rotterdam implemented useful voluntary programmes, and Stockholm required more time to evaluate the effectiveness of its voluntary approaches in increasing green roofs. A voluntary approach for retrofit and a mandatory approach for new build developments are suggested as recommendations for Australian cities. Given the increases in green roofs internationally, similar increases can occur in Melbourne and Sydney in Australia, and these findings may be transferable to other global cities investigating different approaches to the increased adoption of retrofitted green roofs.