A Study of Green Roof Hydrologic Performance in the Cascadia Region

To evaluate the viability of green roofs for stormwater management and low impact development (LID) in the Cascadia region, Seattle Public Utilities (SPU) initiated the Green Roof Performance Study (GRPS). The GRPS research project, led by Taylor Associates, Inc., is currently collecting up to three years of continuous hydrologic data at five different buildings with green roofs located throughout Seattle. The data set from each roof will include rainfall, supplemental irrigation, solar radiation, wind speed, air temperature, relative humidity, and runoff. These continuous hydrologic records will be used to calibrate a continuous hydrologic model, which in turn will provide a long term simulation of green roof performance based on a regional 40-year rainfall record. Such long-term monitoring and simulations of green roof performance have not yet been developed in literature or widely used as a basis for zoning, design criteria, or building code incentives. Preliminary results from the GRPS show that green roofs can reduce the volume and peak flow rates of stormwater runoff on an individual storm basis and over the course of a year.