July 25, 2019

Green Roof Database and Evaluation

Green Roof Survey: The 2010 Seattle Green Roof Survey provided a snapshot of green roofs for the City of Seattle creating a baseline understanding from which to build a more comprehensive inventory and tracking tool for the city’s green roof built stock, green roof benefits and challenges, and the emerging green roof industry. Information about existing green roofs in Seattle was collected using a combination of online research, phone interviews, and site visits. The total green roof area at the time of the report was 359,375 SF (~8.25 acres), not including large lidded areas such as the reservoirs and Freeway Park.

Green Roof Performance Studies: In partnership with Snyder Roofing of Washington, LLC, Green Futures Lab associates examined effectiveness of four (4) vendor-prescribed green (garden) roof systems. The initial phase of this study established a baseline for the roofs’ abilities to reduce, detain, and clean storm water runoff, determining their influence on temperatures associated with urban heat island effects, the long-term durability of green (garden) roof materials and their required maintenance. A fifth experimental plot will use a growing media and plant palette reflecting Puget Sound | Georgia Basin PS|GB native conditions that will be hydrologically and biologically compared with the four commercial plots. The findings and methodology developed in this project will be used to create a green (garden) roof performance evaluation protocol tailored to the PS|GB region, as well as a standardized evaluation process for comparative analysis. In future projects, this evaluation process will be applied to other regions and climatic settings, furthering contemporary discourse on available green (garden) roof technologies.

This research augments a body of current research seeking to address questions such as: How is Seattle contributing to the greening of our nation’s urban rooftops? What successes and challenges are associated with the application of green roofs in existing projects and new development in Seattle? Could the combined area of existing and proposed green roofs provide significant watershed and public infrastructure benefits? This inquiry will help to develop a context for the further development of green roofs in Seattle and elsewhere.