Rooftop innovation cools from top to bottom

  • Published
  • By Thea Skinner
  • 21st Space Wing Public Affairs staff writer
PETERSON AIR FORCE BASE, Colo. --  From a bird's eye view one can see the roof of the 21st Space Wing headquarters building grows in a multitude of colorful shades. Sedum plants populating the roof are part of a GreenGrid roof case study, which has drawn Department of Defense-wide interest. 

Eight different species of plants were placed on the roof of building 845 in December 2007, and the case study may drive the Air Force to replicate the design at other Air Force installations. A one-year study accompanying the roof project shows the building may see reduced energy consumption. This data could drive new building construction standards at other military installations to utilize green roofing systems. 

"The goal is to create a microclimate - that provides a conducive environment lowering roof temperatures," said Randy Hawke, facilities excellence architect for the 21st Space Wing.
Although the plants are propagating on the roof surface, the plants are not completely covering the more than 2,100 plastic trays on the 19,000 square-foot roof. Once fully established, the vegetation will decrease solar heat gain in the building during the summer and decrease heat loss during the winter.

Energy reduction inside the building is estimated at 7 percent, according to a 2009 Comprehensive Green Roof Study draft report. The report was created by Tetra Tech Engineering and Architecture Services, and the Air Force Civil Engineer Support Agency. The report indicates approximately 169 percent savings in a return on investment to include roof replacement and energy savings throughout a 40-year period.

For the hottest day in August 2008, the green roof surface temperature was 100 degrees, compared with the black conventional roofing system of the 21st Mission Support Group, which was 164 degrees, according to the report. 

"Plant coverage acts as an insulator. We should be at 100 percent coverage by next summer," said Phil Chase, 21st CES, Asset Management Flight, pollution prevention, solid waste and hazardous materials program manager. "You think you are on an Air Force Base, but you are at a plant nursery on a roof."

Peterson's green roof was touted in the July 7 Committee on Appropriations report identifying Peterson's Energy Saving efforts with the green roof and other initiatives suggesting to incorporate green technologies in all military construction projects and recommends Senate passage of the bill - S. 1407.

The Department of Defense is the nation's single largest consumer of energy, accounting for approximately 78 percent of the federal government's energy usage, according to the 2010 report of the Military Construction and Veterans Affairs and Related Agencies Appropriation Bill.

Among the many energy conservation measures that DoD is exploring, the committee encourages additional investment in green roof, cool roof and photovoltaic roof technology, according to the report.

The green roof is also reducing storm water runoff, improving air quality, and extending the life of the roof. The plants thrive mainly in rocks, so the roof appears as a flowery desert environment with no insects.

Although sedum was selected due to its drought tolerance, the plants are watered through a drip system that is turned on by a meter when it detects prolonged dry periods.
"The study is a one-year period, which is not long enough to assess the actual life cycle of the roof and its advantages," Mr. Hawke said. 

The general life cycle of such an analysis project should be five years, and a follow on study is being pursued to acquire a more accurate assessment of energy savings, storm water retention along with the life cycle cost of the roof. 

By Summer 2010 the plants should become self-sustaining and better assessment results will occur. Although used mainly in Europe, green roofs are gaining worldwide attention. Toronto, Canada, may require that all buildings have green roofs and several Air Force bases such as the National Museum of the U.S. Air Force at Wright-Patterson Air Force Base are considering installing green roofs. 

"We have to be responsible with our resources," said Col. Emily Buckman, 21st Mission Support Group commander. "If the green roof helps save taxpayer money, as well as helps the environment, we are on the right path."

 

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