Soil for over structures may have a weight requirement. Until recently to provide a lightweight soil meant to amend sand with peat moss or pine bark. Over a short period of time, organics will decompose creating two problems for roof top gardens. First the amount of mix decreases, requiring replacement which means usually carrying product to the top of the structure in bags. The second of the most concern, as the organics break down, the fines filter out down to the separation fabric. Once on the bottom, the fines decompose further creating a slime which may impede the drainage causing the water to build up in the soil. This will increase soil weight and create plant health problems. Some roofs have developed leaks due to this occurrence. Today research has shown that a blend of coarse sand, expanded slate and only 5 to l0% organic matter is best suited as a roof top planting media. The separation fabric over a lightweight aggregate drainage ballast should be a woven product that allows the smaller fine particles to wash through harmlessly flowing out down the drain. Stalite expanded slate has been specified and successfully implemented into three very large rooftop projects. One being the Nimitz Library at the U. S. Naval Academy, the others being the Georgia International Plaza in Atlanta and North Park 400. Georgia International Plaza Project Designer: Leslie Design Associates, Inc. Landscape Contractor: SKB Georgia International Plaza (during installation) Georgia International Plaza (after installation) The Georgia International Plaza is a seven acre rooftop garden over a 2,000 car parking deck. The project is situated between the Georgia Dome and the World Congress Center. During June of 1996, over 12,000 cubic yards of lightweight soil mix was placed by conveyor and compacted on the rooftop plaza. The plaza portion of the project was designed by Leslie Design Associates, Inc. in Atlanta. The mix consisted of 50% sand, 35% PermaTill (Stalite 5/16" expanded slate), and a 15% organic amendment. Several acres of Emerald Zoysia sod, 192 trees, 7,000 shrubs and 24,000 herbaceous seasonal color plants were planted just a few weeks before the Olympics started. In 98 degree temperatures, the sod was laid and trees were planted in full leaf. This plus constant irrigation normally would have taken its toll on newly planted material. Add the foot traffic of millions of Olympic visitors would make you think the soil under the turf would be compacted to the point that no roots would penetrate it. After the Olympics, only one tree died and the turf recovered remarkably well. By the next spring the trees, turf, and other plant material were thriving. Root penetration was extensive. This remarkable growth continued throughout the summer. Because of the porosity of the soil, the heavy irrigation to establish the turf had no adverse affect on the trees. This is one of the many benefits of an engineered soil mix. Soil percolation and water retention can be determined in the laboratory, then the mix can be designed to meet the specific needs of the micro environment. North Park 400 Roof Garden Project Designer: Roy Ashley & Associates, Martin Haber, ASLA Landscape Contractor: Ruppert Landscape Co. On the top floor of the building are dozens of large planters. 2000 cubic yards of Mr. Natural Lightweight Soil Mix containing 55% PermaTill was craned up to the roof in bulk sacks and poured out the spouts into the planters. The entire job was completed four months ahead of schedule. The plants began rooting into the new mix quickly and thrived. By the next season the plants were completely established meeting the intentions of the design. The project won the Georgia Green Industry Association’s Grand Award. North Park 400 Roof Garden (Before Application) North Park 400 Roof Garden (After Application) Click Here For Locations Where Stalite Lightweight Soil Mix Has Been Applied! Email to receive free specification guidelines for Stalite Lightweight Soil Mix for Roof Gardens.