CITY'S GREEN ROOFS
• Capital Mark Bank, 801 Broad St.
• River Street Architecture, 714 Cherry St.
• Creative Discovery Museum, 321 Chestnut St.
• Outdoor Chattanooga, 200 River St.
• Plow Building, 1635 Chestnut St.
• Hamilton County Health Department, 921 E.Third St.
• Terminal Brewhouse, 6 E. 14th St.
• Crash Pad, 29 Johnson St.
• Mary Walker Towers, 2501 S. Market St.
Chattanooga's City Council building is expected to be sprouting a new kind of green image in coming months when an old roof is exchanged for a garden.
The $230,000 to $250,000 roof -- mostly paid for with Department of Energy stimulus money -- will triple the normal life-expectancy of the roof, save an estimated 25 percent on costs and reduce the city's tab for stormwater runoff fees.
It will be downtown Chattanooga's 10th green roof.
And some officials hope it will lead a charge for more green change.
"We're calling for 100 green roofs in coming years," said David Crockett, director of the city's Office of Sustainability.
But the idea -- already approved by the City Council in concept -- faced questions in the council's committee agenda Tuesday. Councilwoman Deborah Scott had questions about the building's structural strength.
Crockett said an engineer's report states the structure is indeed strong enough to hold the weight of a wet, 6-inch-thick growing medium and plants.
"I just want to know if we're sure, and I haven't had time to read what you sent me," Scott said. "I want to know about the warranty. I'm going to ask that we defer this item for now."
Crockett said he hopes to place the resolution for council members to approve the design architect back on the agenda next week.
"This is new for us, but it's not new," he said. "Chicago has 1,000 green roofs, and Europe's been doing this for 200 years."
How Green Roofs Work
Commercial green roofs are not roof gardens.
Most of them aren't meant for foot traffic, although they are inviting enough to roll on with their lush sedums and occasional wavy perennials.
Think of them instead as green skins, layers of living insulation.
Chicago City Hall's 20,000-square-foot green roof was installed in 2000.
In 2006, Chicago officials reported that the city had saved $25,000 in energy costs in the first five years of the roof.
Green roofs help reduce energy use by insulating buildings from extreme temperatures.
In Chattanooga's blistering summers, a rubberized roof -- especially a black one -- can generate temperatures of 175 degrees right where the building's air conditioning equipment is struggling to cool inside air down to 70 degrees.
Studies have shown green-roof temperatures can be nearly 100 degrees cooler than a black rubber or tar roof.
The roofs also help control stormwater runoff, catching and holding for slow release first inch of rainfall in any 2-inch rain event -- which includes most of Chattanooga's two-day rains.
"They don't really 'hold' the water, so much as they slow it," said Sabrina Novak, environmental scientist at the Chattanooga-Hamilton County Health Department. Health Department. Workers began Wednesday installing a green roof on 6,000 square feet of the health department building.
Runoff from Chattanooga's 52 inches of annual rain runs off roofs and pavement to the city's decades old combined sewer and storm tunnels and into football field-sized concrete caverns beneath the city's surface.
If the rains are moderate, the combined sewer and rainwater runoff is released slowly into Moccasin Bend Sewage Treatment Plant, where it is treated and allowed to flow on into the Tennessee River.
But in heavy rains, the sewer-tainted runoff overflows into local creeks, streets and the river -- which also is the source of drinking water for Chattanooga and other cities downstream.
"There is no 'away,'" Crockett likes to say about where stormwater, sewage and garbage go. "That's why we have to be smarter than we've been."
Novak says the health department's roof will include a patio-like area near its center that will serve as an occasional outdoor conference room and food education classroom.
"We're going to put herbs and other edibles -- like tomatoes -- in the planters to help teach about container gardening and eating healthy," she said. "We're about a healthy person and individual, but rolled into that is a healthy environment. This is our way of educating people that a your healthy environment is always a component to healthy people."