Environ. Sci. Technol. http://doi.org/nq9 (2013)

Rapid urbanization leads to increasing greenhouse gas emissions from rising energy demand and greater health impacts caused by deterioration of air quality. Green roofs can alleviate those problems, but upfront costs and lack of information delay wider adoption.

Jeffrey Mullen of the University of Georgia, USA, and colleagues compared the costs of conventional roofing with those of vegetated roofs (in present value terms) across 138 buildings in Atlanta under different scenarios. Choosing the green option saves on installation and maintenance costs (net private benefit) for buildings' owners for small roofs, but such benefits shrink with increasing roof size and vary across scenarios. The community at large would generally save storm-water management, air-quality and emissions costs (net public benefits) with little variation across scenarios. They found that government subsidies can support green roof adoption, but are most cost-effective if offered only to owners with no monetary incentive to invest in the technology.