Comprehensive Benefits of Green Roofs

Green infrastructure uses vegetation, soils, and natural processes to manage water and create healthier urban environments, providing alternative stormwater management technologies (EPA 2014). Green roofs are a major component among green infrastructure technologies, and, while providing traditional roof services, also contribute to stormwater management. Research conducted assesses specific stormwater benefits of green roofs, providing information on nutrient leaching from media. Research was also undertaken to analyze potential energy benefits through side-by-side comparisons of full-scale white, traditional black rubber, and green roofs. Results revealed a 56.2 cm/yr average runoff reduction for the growing media alone, and a 61.6 cm/yr average runoff reduction for vegetated green roofs in the mid-continent Missouri climate. Roofing media selection greatly impacted leaching of phosphorus, nitrogen, suspended solids, and organic carbon from the tested green roof media. Thermal properties were investigated at the building level, as were benefits related to urban heat island effect. In a unique research endeavor, water and energy models are combined to illustrate impacts of evapotranspiration (ET) on green roof temperatures and urban heat dissipation. As ET is dependent on a variety of climate parameters including temperature, humidity, wind speed, and solar radiation, the potential to dissipate energy from a roof surface by means of water vaporization was modeled and latent heat fluxes were projected. Models using climate data may be used as predictive tools on impacts of green roof design and can be applied in stormwater management, allowing green roofs to reach maximum benefits of minimized nutrient loading, runoff reduction, peak flow attenuation, reduction of urban heat island effects, and economic savings. Findings presented raise societal questions as many ancillary benefits such as aesthetics and urban energy dissipation are society-level benefits, yet capital costs as well as operation and maintenance costs are generally incurred by the building owner.