By David Pendered
Atlanta is in the early stages of renovating the green roof atop Atlanta City Hall. Plans call for more seating, the removal of invasive weeds and the installation of plants with a vibrant mix of colors and bloom times.
Weeds have become a major concern. Weeds earned their own section in the city’s request for proposals:
- “Annual and perennial weeds have become a significant problem on the roof. Renovation should include a strategy to remove existing weeds, control future weeds and address the weed seed bank in the soil media.”
The initial pilot green roof opened in December 2003 as the first city-owned green roof in the southeast. The project covered 3,000 square feet and was intended to provide reliable technical data on the benefits and detriments of installing gardens atop roofs, according to a report by greenroofs.com. The project included 227,770 pounds of material; more than 2,800 plants representing 31 species used, and a soil depth ranging from 3 inches to 10 inches.
The green roof has been altered in the intervening years and specific plans of those alterations are not available, according to the city’s request for proposals.
For example, Atlanta has called for an appropriate irrigation system to be installed. Taping into a water supply might require the vendor to poke around the roof, according to the RFP:
- “Note: Two existing hose bibs on the green roof will provde the source of water for the irrigation system. Supply lines were installed at the perimeter of the roof at construction, however, size, material, and exact location of these supply lines is unknown.”
As for seating, the city intends to replace the existing furniture with a “modern” design that complements the style used in the nearby cafeteria. The furniture is to be anchored or of a weight sufficient to prevent it from being blown off the roof.
The current paved areas aren’t to be altered. However, additional seating or bench pads could be installed on the west wing.
The current plan is to update the planting plan based on a plant palette the city will provide. Of note, the RFP states that the key elements of the planting design include:
- “Plantings should provide a vibrant mix of colors, textures, bloom times, and multi-season interest;
- “Plantings should complement and enhance the use of the green roof as an outdoor easting and sitting area;
- “Remove all Yucca, Junipers and Rosemary, as well as privet and other weeds, dead plant material, and the raised garden beds on the west wing. Soil in raised beds will need to be removed from roof and disposed of off-site;
- “Consolidate and reuse existing plantings where appropriate along with new plantings. Plants to be kept and reused shall be clearly denoted on planting plan;
- “Plants must be able to thrive on the green roof and provide maximum storm water management benefits;
- Plants must not pose a future hazard to the roof membrane;
- Full vegetation coverage of the roof should be achieved as soon as possiblel. The Plant Coverage Goal is defined as 90 percent to 95 percent non-weed vegetation coverage of planted area. Contractor will state in proposal how long it will take them to achieve this goal.”