Going green: Is that a vegetable on the roof?

UAB Facilities and researchers from Civil Engineering are undertaking a 12-month green-roof research project to evaluate energy-efficient roofs for campus and lead the charge in the Southeast against “heat island effect.”

“Our goal is to get enough data to use to create new standards for UAB roofs that will be more energy-efficient and cost-effective,” says Olen Pruitt, executive director of Facilities Management. “We want anybody in this climate region to be able to use our data and apply it to their roofs.

“We’re trying to do our part to promote green at UAB, but we also believe we should lead and provide data to others.”

Heat island reduction
Heat island is a term describing the phenomenon in which urban and suburban temperatures are 2 to 10 degrees Fahrenheit (1 to 6 degrees Celsius) hotter than nearby rural areas. Elevated temperatures alter communities by increasing peak energy demand, air-conditioning costs, air-pollution levels and heat-related illness and mortality.

Part of what elevates those temperatures is the surface temperature of roofs, which can reach between 140 and 160 degrees Fahrenheit in the summer, says Roger Brown, UAB’s roofing specialist. To combat the heat island effect, the Environmental Protection Agency recommends installing cool or vegetative green roofs, planting trees and vegetation and switching to cool paving materials to reduce the negative effects of heat islands.

Planted rooftops remain significantly cooler than those constructed from traditional heat-absorbing materials, and green roofs reduce summertime air-conditioning demand by lowering heat gain to the buildin

Test roofs
UAB Facilities recently installed 15 miniature test roofs with different types of green or sustainable roof systems atop the Chemistry Building, and researchers and students in Civil Engineering monitor them. Each test-roof box measures 4 feet by 8 feet, is constructed of plywood and is insulated similar to most UAB buildings.

Inside each plywood box is a wireless temperature sensor that is recorded and trended by a remote computer

“Data is recorded every 10 minutes for all 15 mini-roofs,” says Robert Peters, Ph.D., professor of environmental engineering. “We have five extra mini-sensors we can move from roof to roof to look at the interface between the insulation and building materials. We’re getting temperatures during the course of the day and during seasons.”

Many different types of existing green-roof systems, including vegetative and white reflective roofs, are being evaluated in comparison to traditional roofs for effectiveness in conserving energy and sustainability. The results will be used to determine the type of roofs to be used in the future.

“This research is very important in UAB’s efforts to reduce energy consumption,” Pruitt says.

Real-world problems
Peters and Pruitt say the students working on this project have been enthused and energized.

“Their energy is infectious,” Pruitt says. “They feel they are working on real-world issues and their work can be beneficial immediately.”

Civil Engineering students examined roofing types in their senior design course this past fall. The course culminates four years of study as a civil engineering student, tying together all of their sub-disciplines.

This past fall, Facilities picked the Hulsey Building as a potential test case to retrofit a green roof. Two student teams studied design codes of the building, determined the load it could support and designed a vegetative or white reflective roof to retrofit the building, factoring the impact of runoff from rain on the surroundings.

Both groups advocated green roofs to help save energy. One selected a conventional green roof, and the other used soil that had broken bricks or brick chips. They also had to incorporate architectural design and consider plant species that might be involved.

Peters has a doctoral and master’s student working on the project, trying to make sense of the temperature and runoff data and using Department of Energy computer code to assess the energy-efficiency of the green-roof materials.

“We want to identify which roof is the best candidate for retrofitting the models we have,” Peters says. “We’re trying different soil materials and plant materials. We’re also capturing samples of the runoff and looking to see if metals and other substances may be in the roofing materials. We’ll be looking at the performance during the course of at least a year.”

Do it yourself
In Chicago and parts of Arizona and Wisconsin, green roofs have been incorporated into certain structures. Pruitt and Peters say not much academic research is being conducted on green roof systems in the South.

“There’s not any real scientific data for this climate,” Pruitt says. “We finally decided the only way for us to get this information was to do it ourselves. Fortunately we are at an institution with the kind of resources at our disposal to make this happen and to do it the right way.”

So is it possible that there could be roofs on campus in five years that have grass and small plants and shrubs?

“It’s definitely possible,” Pruitt says. “We’re looking at the possibility of putting a vegetative roof on one of the buildings here at UAB as a pilot. When retrofitting a green roof on any building you have to be sure the structural strength of the building will support it. So some buildings may be suited for it, and some may not.

“But if we can prove this works, then buildings that are being designed now or in the future – on campus, in our community or in the Southeast – can be stressed to handle the load of a green roof.”

As someone who’s spent more than one Alabama summer day working on a 140-plus degree roof, Brown is excited by the research, and he’s glad to be helping Civil Engineering and Facilities with the project. The test roofs are impressive, he says, and the possibilities are intriguing.

“The green roofs and the white reflective roofs certainly look real neat,” he says. “They would look nice on any building we have.”