City Hall’s roof greenery flourishes five years later

You can’t fight City Hall, but you can grow stuff on the roof.

Atlanta City Hall’s large-scale “green roof,” installed on the patio outside the building’s cafeteria in 2003, is flourishing.

Bill Brigham, the city’s landscape architect who designed the project, said the planting has survived high winds, extended drought and the once-a-decade effort to pressure wash the building.

“The roof is a utility area. These things are going to happen,” Brigham said philosophically.

The xeriscaped garden contains about 2,800 plants representing 31 species. Brigham said he has had to spot-water it maybe 10 times in the five years since it was installed.

City Hall’s green roof is a demonstration project, intended to show the way for others, but Brigham said he has learned a great deal from it.

For example, how did weeds manage to climb 70 feet into the air and insinuate their way into the green roof? The first clue was that the intruders were growing next to benches used by people visiting the roof (often employees on cigarette breaks). Brigham deduced that weed seeds were riding up the elevators on people’s shoes and then being deposited on the roof.

Or this one: “On two of the corners, there’s rosemary,” he said. “You know, rosemary’s pretty hardy. But in this one corner, it’s dead as a hammer. What’s that about? It’s City Hall Tower. I don’t have any scientific research to document this, but during the afternoon, the tower shades that one area for about an hour and a half, while the other one’s out there baking.”

The green-roof idea is growing on people. Gwinnett County’s Environmental and Heritage Center has one, as have Decatur’s City Hall and the High Museum. Plans also call for green roofs at Chattahoochee Nature Center and Atlanta Botanical Garden.