Atlanta City Hall, Atlanta, GA

 

Panoramic View, 12.17.03; All Photos Courtesy Ben Taube, City of Atlanta, Unless Otherwise Noted.

A Cool Roof in a Hot City:  The Southeast's First Municipal Greenroof
By Benjamin Taube and Janet Ward

It’s hotter in the city. Expanses of concrete and asphalt-shingled roofs, combined with a lack of open greenspace, produce a phenomenon that has been documented by everyone from local meteorologists to scientists at NASA. Called the “Heat Island Effect,” it raises urban temperatures to much higher daily levels than those enjoyed in less developed areas.

The phenomenon, along with urban ills like degraded air and water quality, can be mitigated by building gardens and protecting greenspace. The problem is that in highly developed urban areas, there is nowhere to put those gardens and no greenspace to protect.

Atlanta officials found a solution in City Hall. Using the fourth-floor roof of the newest part of the building, they constructed a “greenroof,” planting more than 2,000 square feet of vegetation, mostly hardy sedums and herbs, and creating a garden in the air.

Although the idea has been incorporated into municipal architecture in cities like Chicago, Portland, OR, and Seattle, Atlanta’s greenroof is the first such project in the Southeast.

Debuting in December 2003 after more than two years of research and planning, the city’s greenroof will serve as a pilot project that its creators hope will generate reliable technical data in areas such as temperature reduction, energy efficiency, and stormwater retention. They also will monitor its effect on roof life and hope to determine which plants work best in the shallow soil of a greenroof. Finally, and most importantly, they hope to show Atlanta’s business community a working greenroof that can serve as a model for similar projects.

The Atlanta project was driven by Ben Taube, the city’s Environmental Manager, and Bill Brigham, its Landscape Architect. It contains 35 varieties of vegetation, mostly hardy sedums and herbs, and was designed as an “extensive greenroof,” which features low soil depths and low-growing vegetation. The project was completed with the assistance of more than 10 companies and vendors who donated plants and other products and services. The City sited the greenroof outside the building’s fifth-floor cafeteria and not atop the main roof so it could serve as a patio.

The greenroof idea is important because Atlanta produces enormous amounts of ground-level ozone every summer and has been designated a “severe” non-attainment area by the Environmental Protection Agency. In 2002, the city exceeded federal ozone standards on 38 days, up from 20 days in 2001.

In 2001, Atlanta joined with the Georgia Environmental Protection Division and other partners in a NASA-funded project to develop and validate an improved urban air quality modeling system using high-resolution remote sensing data. The project concludes this year with what the city hopes will be a system that allows stakeholders to quantify the impact of land cover and land use changes on air quality, particularly ground-level ozone.

Taube and Brigham also expect the greenroof to play a significant role in mitigating stormwater problems by absorbing water that normally would wash into the sewer system. Additionally, they hope that eventually the city will create an incentive program – like those in other cities – for commercial, residential and industrial greenroof projects. Such incentives will become increasingly popular, since the city is working on creating a stormwater utility that will base future fees on impervious surface calculations. Traditional roofs represent large impervious surfaces, so greenroofs can be significant factor in off-setting future fees.

Jack Ravan, commissioner of the Department of Watershed Management, which sponsored the project, is a serious fan of the greenroof idea, as is Atlanta Mayor Shirley Franklin, who has indicated an interest in growing tomatoes on the roof. “Greenroof technology is a viable tool for mitigating the urban heat island effect and for dealing with stormwater problems,” says Ravan, who also is a former EPA Regional Administrator.

Atlanta’s summers can be brutally hot, and it is not uncommon for temperatures within the city core to be higher than those in the surrounding suburbs. The greenroof serves as a heat-absorbing buffer and an environmentally friendly replacement for asphalt or concrete roofing. “The [temperature] reductions will come in the summer when we have the intense sun,” Brigham says.

The project represented a relatively minor expenditure, primarily because, with outside bidding starting at $163,000, the city focused on in-house program management, construction and maintenance. The City received approximately $55,000 in donated products, a construction grant of $18,000 from the State, and a matching grant of $18,000 from the Department of Watershed Management. The project cost a total of $110,000, but minus the donations and grants it cost the City $19,000. The city’s Parks and Recreation department will provide what little maintenance the roof is expected to require.  Click here to view the Cost Breakdown pdf.

The greenroof was constructed in four phases over a six-week period. After a structural analysis concluded that the roof could support “extensive” soil (the lighter of the two types of soil used in greenroof applications), workers removed concrete ramps and asphalt, replacing it with waterproofing material donated by Teaneck, N.J.-based KEMCO Kemper Systems. The construction team then plugged existing drains and flooded the roof’s surface to ensure that there were no leaks.

Other material and services were donated by local firms Excel Electrical (electrical conduit), Saul Nurseries (plants), It'Saul Natural (lightweight engineered soil), JDR Enterprises (drainage system), Unique Environmental (plant installation), Flintstone Pavers (paver installation), Sims Stones (pavers) and by the City’s Department of General Services (labor).

On February 19, 2004, the City of Atlanta hosted a roundtable discussion on the City Hall greenroof project.  The Atlanta Chapter of the U.S. Green Building Council (USGBC) sponsored the event, and the audience consisted of product manufactures, developers, architects, engineers, municipal government staff, City Council representatives, and contractors.  The speaker panel consisted of Ben Taube; Janet Faust of JDR Enterprises; Ernie Higgins of It'Saul Natural; and Chris Kramer from Kemper waterproofing systems.

Participants had an opportunity to speak for 10 minutes on their product and use on the City Hall greenroof.  Ben Taube started off the roundtable with a discussion of the City’s sustainability initiatives, which includes the development of another greenroof.  Additionally, Ben discussed the greenroof project and construction steps.  Next Janet Faust discussed the drainage layer that was used on the City Hall greenroof project; the J-Drain system was supplied by JDR Enterprise and was applied on the entire surface of the roof deck.  More information on the J-Drain system can be obtained from www.j-drain.com.

Following Janet’s discussion, Chris Kramer from Moon and Associates representing Kemper Waterproofing systems discussed the waterproofing layer used on the project.  The waterproofing system is a liquid applied membrane consisting of three layers, and is certified for contact with potable water.  More information is available at www.kempersystem.com.

The last presentation was a discussion on the structural soil mixture that was used on the project.  The growth media was supplied by Ernie Higgins from It'Saul Natural located in Dahlonega, Georgia.  Information on the soil can be obtained from Ernie at ewhiggins@earthlink.net.

Concluding the speakers’ presentations the audience participated in a question and answer session.  The majority of questions centered on the construction stages of a greenroof as well as product specific information regarding the soil and drainage layer.  Each participant showed an extreme interest in the greenroof project and took away a good basic education on the means of designing and constructing a greenroof.

From February 18^th through 22^nd, 2004, the City of Atlanta Department of Watershed Management participated at the Southeastern Flower Show with a “Discovery Garden” exhibiting the City Hall greenroof.  Throughout the 4-day show, the exhibit was visited by a variety of landscape professionals and residential homeowners.  Visitors to the “Discovery Garden” were very excited to see that the City was taking steps to mitigate the urban heat island.  Many visitors wanted to learn about the variety of sedum plants that were used on the project.

“It’s going to be a pleasant place to be this spring and summer,” Taube says. “We’re hoping other people see it and say, ‘Hey, I want one of those,’ but we also want them to realize the many environmental benefits offered by greenroof systems.’”

Benjamin Taube is the City of Atlanta’s Environmental Manager and can be reached at 55 Trinity Ave. SW, Suite 5900, Atlanta, Georgia 30303; Phone 404.330.6752; Fax 404.658.6406; or BTaube@AtlantaGa.Gov.  His responsibilities include developing and enhancing environmental initiatives and policy in Atlanta.

Janet Ward is the Department of Watershed Management's Public Information Manager and can be reached at 55 Trinity Ave. SW, Suite 5400, Atlanta, Georgia 30303; Phone 404.330.6620; Fax 404.658.6515; or JWard@AtlantaGa.Gov.  Her responsibilities include public relationship and outreach for the Department.