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PSU Researchers Evaluate Green Roofs
Author: David Santen, Office of University Communications (503-725-8765; santend@pdx.edu)
Posted: March 12, 2009

(PORTLAND, Ore.) – The advent of vegetated (green) roofs, replacing conventional commercial roofing materials with a layer of soil and plantings, holds much promise for efforts to reduce the carbon footprint of buildings, which are currently responsible for 40 percent of total energy consumption in the U.S. and European Union.

Green-roof advocates herald benefits such as increased energy efficiency and reduction of storm water runoff, dampening of the urban “heat island” effect, and extension of the roof’s life expectancy. More intangible are the relation between eco-roofs and improvement of air and water quality, creating arable land for commercial crop production, creating wildlife habitats and recreational areas, and the improved aesthetic values of green roofs.

But the fast-growing popularity of this green building feature has outpaced rigorous measurement and evaluation of its effectiveness. Researchers at Portland State University are working to close this green-roof information gap.

The green roof research effort at PSU includes a multidisciplinary team of faculty and students, led by David Sailor (Mechanical Engineering), and with support from Graig Spolek (Mechanical Engineering) and David Ervin (Environmental Science), among others.

This team has developed models of the energy and environmental performance of green roofs, based on variables such as roof materials composition, soil moisture content, climate and building size. These models, versions of which have been integrated into the U.S. Department of Energy’s EnergyPlus building energy simulation software, enable users to better determine environmental and economic benefits of green roofs.

“For the first time, developers and building designers can quantitatively assess the building energy consumption implications of green roof design choices,” says PSU’s Sailor. “Hopefully, the availability of this information will reduce barriers to widespread adoption of green roof technologies .”

Work at PSU draws on both fieldwork and lab simulations to produce meaningful data and models that measure everything from rainwater retention and filtration to the thermal insulating properties of different types of plants. The research group’s studies have also assessed lifetime costs of green roofs versus conventional roofs, accounting for materials, installation, maintenance, energy savings, impact on vacancy rates and other variables.

Some of that fieldwork happens right on campus. The research team installed a weather station atop PSU’s The Broadway, a 10-story mixed-use academic and housing facility, with an 18,000 square-foot eco-roof. The station has generated over a year of data critical to assessing rooftop conditions: atmospheric temperature, humidity, wind speed, wind direction, solar radiation, precipitation, and barometric pressure. In addition, The Broadway weather station logs soil temperature and moisture at two depths as well as the leaf wetness. The station allows for testing and validation of models developed.

This green-roof modeling research has garnered funding from a variety of government, industry and nonprofit sources, including the Oregon Built Environment and Sustainable Technologies (BEST) signature research center (news release), the James F. and Marion L. Miller Foundation (via a competitive RFP process administered by PSU’s Center for Sustainable Processes and Practices), the City of Portland’s Bureau of Environment Services and Office of Sustainable Development, Ecoworks Foundation, Gerding Edlen Development and Quantec, LLC (now The Cadmus Group).

Recently the U.S. Green Building Council committed ~$150,000 for David Sailor to create a “Green Roof Energy Savings Calculator,” a simpler and more widely available version of the EnergyPlus simulator, designed for a broader audience. The project was one of only 13 funded nationwide, selected from 216 pre-proposals and 39 full proposals.

Demonstrated excellence in green roof modeling has also enabled the green building research group to expand, establishing the Green Building Research Lab at PSU in late 2008. Located in the engineering building at the Northwest Center for Engineering, Science, and Technology at PSU (a LEED Gold certified facility), the Green Building Research Lab will house the computational and experimental infrastructure for research on building envelopes; passive, active, and hybrid HVAC systems and controls; buildings’ interactions with local environments; and indoor environmental quality. The facility will draw faculty collaborators from across the Oregon University System, and is intended to facilitate university-industry partnerships

For more information on green roof modeling research, and on the Green Building Research Lab at PSU’s Maseeh College, visit www.greenbuilding.pdx.edu or contact David Sailor, Department of Mechanical and Materials Engineering, Portland State University (503-725-4265; sailor@cecs.pdx.edu).

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