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Comparisons of Thermal Properties and Stormwater Runoff of Butler College Green and Conventional Roofs, Eileen Zerba

As part of Princeton's Campus Sustainability Master Plan, Butler College residential complex with many sustainability features was designed to use 30% less energy than would be expected under current building codes.  The projected savings are partly attributed to extensive vegetated roof designs on 50% of the complex and a stormwater cistern that collects and recycles rainwater to irrigate landscaping.  The layout of paired L-shaped buildings with similar roof sizes and angles, one a green roof and one a conventional roof, presents a unique opportunity to contrast biophysical and economic benefits of green roofs. The vegetated rooftops planted with 14 varieties of hardy sedum are instrumented to measure temperature, heat flux, and soil moisture, within the roof layers from the surface to the building interior.  The conventional roof mirrors this configuration minus the soil sensors.  Mock roof models are used to measure stormwater runoff, and meteorological sensors define environmental parameters to address two major questions.  First, how well do green roofs cool or insulate compared to conventional roofs?  Seasonal data will be provided to address the effectiveness of green roofs in decreasing energy demands for heating and cooling and savings in building life cycle costs.  For summer months, data indicate decreased thermal variability, a 30% cooler surface temperature, and as much as 50% cooler membrane temperature for the green compared to the conventional roof.  Second, to what extent do green roofs mitigate stormwater runoff and improve water quality?  Results of the quantity of the water coming off the green roofs compared to conventional roofs will be given for various precipitation events and soil moisture profiles.  Preliminary data indicate the green roofs demonstrate delayed runoff and approximately a 60% reduction in peak stormwater runoff. Please RSVP to Ildi Kohles ( ) no later than 4 p.m., on Apr. 20, 2011.

Location: Guyot Hall, Room 154

Date/Time: 04/22/11 at 12:00 pm - 04/22/11 at 1:30 pm

Category: Forums

Department: Energy Group