HQ keeps cool under green roof

  • Published
  • By Lea Johnson
  • 21st Space Wing Public Affairs staff writer
PETERSON AIR FORCE BASE, Colo. --  The expanse of flora on the roof of the 21st Space Wing Headquarters building is a surprise to those who don't know it's there. There are 2,100 trays of sedum plants covering most of the 19,000 square foot roof, but it's more than a rooftop oasis.

The GreenGrid roof system was installed in December 2007 as part of an Air Force Civil Engineer Support Agency grant.

Eight species of sedum plants fill the trays that cover the roof. Randy Hawke, Facilities Excellence Architect for the 21st Space Wing, said sedum, a regional high desert plant, was selected because of its drought resistance.

A year-long study took place in 2008, comparing temperatures of the green roof on the Headquarters building and building 350.

"The goal is to create a microclimate that provides a conducive environment, lowering roof temperatures and minimizing the "heat island effect" lowering the overall carbon footprint of Peterson AFB," said Hawke.

According to Hawke, on the hottest day in the summer of 2008, the temperature of the roof on building 350 was 185 degrees, while the temperature of the green roof was only 100 degrees.

Almost three years after the study, the sedum on the roof is still flourishing but the results of the data are inconclusive and Hawke is looking for the funding to do a follow-on study.

"It would validate the baseline and then it would start tracking the actual savings. We found some flaws in the original study that we could correct with an additional study," Hawke said.

Several changes would be made if a second study were to happen. First, the control building would be switched, Hawke said. Building 350, the control, has a metal deck roof while the Headquarters building has a concrete deck. The new control would be a building with a concrete deck similar to the green roof.

Second, the set-up of the sensors would be corrected. The original study didn't measure the plenum space, a key piece of data needed for accuracy. Phil Chase, 21st Civil Engineer Squadron environmental program manager said, "Plenum space is the space above the suspended ceiling to the actual roof. So it's a huge area and we're not measuring the impact that the green roof has on that particular area."

In a future study, the sensors would also be measured in real time, opposed to being downloaded to a computer and then calculated.

For now, it's hard to tell the full benefits of the green roof without another thorough study, but Hawke believes the benefits are there. According to Hawke, the headquarters building has seen a decrease in energy use but without another study, he doesn't know how much of that is from the green roof and how much is from the installation of new windows and insulation.

The sedum plants have not yet reached 100 percent coverage of the roof, Hawke said. There has been some plant loss due to an exceptionally dry winter this past year, but Hawke and Chase are working to keep the remaining plants growing. As the roof becomes more covered, the energy savings should continue to increase.

But the savings come from other areas too.

"UV light is one of the leading causes of damage to roofs," Hawke said. The plants help protect the roof membrane and will extend its lifespan.

Additionally, the roof helps reduces storm water runoff and improves air quality.

Until another study can be done, Hawke and Chase will continue to care for the roof and push for partial green roofs to be installed with future building projects.

"You cannot tell me that the green roof is not making an energy saving impact on the HVAC systems in the building," Hawke said.

 

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