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18 January/February 2017 Landscape and Irrigation www.landscapeirrigation.com GREEN ROOFS aggregates, to design a solution-based design/build plan. A partitioned, extensive green roof was conceptualized as the crowning glory of the newly renovated historic building's most walkable and traffi cked exterior area. Handling the heavy weight An initial challenge was to address the weight-bearing load of the green roof and its contents to guarantee not only the health of the slated live plant material, but also the integrity of the roof 's structure. The weight of the completed project would comprise many components and elements, notwithstanding that which would be associated with the green roof 's soil. When wet, regular soil alone would present a weight factor beyond the roof 's capacity. The density of wet soil differs from dry density in that it is far more compact and its overall burden is strongly overwhelmed by the moisture content of the soil. Storm water runoff also was top of mind for the project team. ERTH Products proposed using HydRocks beneath the surface, which would allow Greenrise Technologies to install a sustainable landscape and address the issues at hand. The pervious green roof would then serve three purposes — making the most of parking space and walkability to the building's numerous rear entrances, providing visitors with a safe green space to enjoy, and offering an invaluable tool to manage storm water runoff. Leveraging rooftop landscapes The living soil specifi ed for the green roof included an engineered mix of biological, organic matter mixed with HydRocks expanded clay lightweight aggregate (LWA), produced through a rotary kiln process in which selectively mined clay is fi red at 2,000 degrees Fahrenheit. Manufactured by Trinity Lightweight, the LWA is a hidden ingredient that equated to the HydRocks' reduced load. "This process produces a consistent and predictable, high- quality ceramic aggregate that is structurally strong, physically stable, durable, environmentally inert, lightweight, and highly insulative," said Jeff Speck, engineer and manager with Trinity Lightweight. "As a fi lter medium, it increases surface area and allows fast, free drainage, helps remove or reduce toxins, and absorbs nutrients for long-term, sustainable water treatment." For site developers, landscapers, green roof builders, and storm water management professionals, this type of lightweight soil mix improves soil's functionality and service life, saving material, labor and transportation costs. The project team specifi ed the lightweight aggregate because its properties supported the physical requirements for developing 14,000 square feet of green roof, while being light enough to satisfy load-bearing codes. Chemical and natural considerations included creating a living soil containing organic macro- and micronutrients, and a diverse population of benefi cial microbes. "A living soil was essential, given it requires fewer chemical inputs, breaks down contaminants, and provides movement within the soil, which increases infi ltration, water holding capacity, and the overall air and water exchange," said Scott King of ERTH Products, LLC. The company's acronym stands for Environmental Resource and Technology for Humanity, and it specializes in manufacturing and engineering specialty soils utilizing compost and lightweight aggregates. King was part of the green roof 's project team. "This design allows for good surface infi ltration of storm water, along with high water- holding capacity, while not creating a continuously saturated soil, which would be detrimental to plant life," said King. "Expanded clay lightweight aggregate in the form of HydRocks is a natural, eco-friendly, non-degradable soil enhancer." Ultimately, the Ponce City Market green roof project team determined in advance that it would provide long-term soil structure with space for air, water and nutrient exchange in the soil profi le. Being a widely developed area, runoff equally had to be considered. Unmanaged storm water could have generated major concerns about both the volume and timing of runoff, as well as potential contaminants carried by the water. The porosity of the engineered soil mix yielded the characteristic of absorbency, allowing water to infi ltrate and dissipate, without causing a fl ow of unwanted rainwater to become problematic. More than meets the eye The extensive green roof, spanning a series of square and rectangle landscaped areas, transformed an otherwise conventional top level of parking into living architecture. But, because replicating nature is complex, Scott McGaughy with Greenrise Technologies had his work cut out for him. "The concept involved a successful green roof consisting of several different sections to work together as a whole," he said. "The challenges were the same as with other green roof installations, but it held some unique traits to address." The site logistics of getting material in and onto the roof proved challenging, and the availability of water for the plants had to be addressed due to the sequence of the building construction. Beginning with a Firestone TPO membrane for waterproofi ng, additional waterproofi ng included a sacrifi cial layer for membrane protection; a root barrier, which prevents plant roots To learn more about this project: Trinity Lightweight: www.trinitylightweight.com ERTH Products: www.erthproducts.com Greenrise Technologies: www.greenrisetech.com Ponce City Market: www.poncecitymarket.com.