A green roof demonstration project

Vegetated roofs are becoming an increasingly viable alternative to conventional impermeable roofing especially for new construction because of benefits related to energy and resource conservation, stormwater management, environmental enhancement, and longevity. To quantify some of these attributes, Millersville University is partnering with the Lancaster County [Pennsylvania] Planning Commission (LCPC) in support of the “Green Roof Project” to estimate the direct environmental enhancement of a local air and watershed resulting from the installation of vegetated roofs. The experimental approach is to conduct measurements over a conventional EPDM rubber roof and compare that to a set of similar measurements over a mature vegetated roof, each for a period of one-month in summer, and normalize the resulting fluxes to the incoming solar radiation. Standard sensors were installed on a 3-meter tower to obtain continuous, high frequency measurements of momentum, sensible heat, and water vapor fluxes by eddy-correlation, net radiation, and conventional meteorological variables (T, RH, p, wind speed and direction). In addition, air sampling canisters were deployed for periods of 12 and 24 hours for follow-on analysis of 61 species of volatile organic compounds using GC/MS in accordance with EPA TO-15. Storm water runoff is quantified by using 2'x 2' test structures constructed to simulate: 1) conventional roofing materials; 2) modular/tray systems, and 3) solid built-in-place structures, and analyzed for water volume/mass, nitrate concentration, and conductivity in close proximity to a rain gauge. The data will be used to test the hypotheses that vegetated roofs significantly decrease the amount of sensible heat flux, terrestrial longwave radiation flux, and water volume, increase the moisture flux, change the speciation of volatiles emanating from the roof, and serve as a sink of nitrate nitrogen. This data will also serve as validation to modeling scenarios that investigate the cost/benefit of expanding areal coverage of vegetated roofs in Lancaster County, and to provide qualitative estimates on the influence of greening on the urban heat footprint. This paper will describe the preliminary results of these analyses, including the modeling effort. In addition, this paper will also report on the education activities associated with vegetated roofs that are taking place in concert with the field measurement project. This project is funded under a contract with the Lancaster County Planning Commission through an Energy Harvest Grant from the Pennsylvania Department of Environmental Protection.