Green Roof tops also referred to as eco-roofs, living rooms or garden roofs are very popular in Europe and has been well established in Germany since the 1960s, successfully implemented on top of schools, office buildings, shopping centers and retail stores. This technology is an attractive way to promote environmentalism while solving the problems of conventional roofs. Green roofs last longer than conventional roofs. Reduce energy coast with natural insulation, create peaceful retreats for people, and absorb storm water, potentially lessening the need complex and expensive drainage systems.
Green roofs also improve air quality and help reduce the Urban Heat Island Effect, a condition in which city and suburban developments absorb and trap heat. The Frankfurt Airport in Germany has installed Green Roofs to buffer noise generated from air traffic. Classification of Green Roofs can be divided into two main categories – extensive and intensive. The Extensive Green Roofs is more common and employs a shallow growing medium of five inches or less. The plants chosen for extensive roofs usually include succulents and moss.
The design of extensive Green Roofs is geared towards low maintenance and limited irrigation. At most, maintenance occurs one to two times a year with limited access to the roof. Intensive roofs use plants that require a growing medium of at least 6-12 inches. These roofs can serve the multiple functions such as providing an outdoor garden space for food production. This type of Green Roof requires more active maintenance with regular watering, fertilization, and pruning. Intensive Green Roofs require more structural support than extensive roofs due to heavier weight loads.
If the intent of an intensive Green Roof is to provide public access than additional design features for safety must be considered. Installation of Green Roofs occurs in one of two ways. First, plants and soil are hauled onto a roof where planting occurs directly on top of the waterproof membrane. The second option involves prefabricated squares with growing medium and plants already sprouted. The squares are hoisted, usually by crane or conveyer belt, onto a roof. Using the prefabricated squares is an attractive alternative as blocks can be easily removed if a leak or another maintenance issue should occur.
The oldest Green Roof in the United States is in New York on top of the Rockefeller Center. The Rockefeller roof top garden was built in 1930, interest in Green Roof technology has only occurred within the last 15 years. Currently, Chicago, Portland and New York are the leaders in implementing Green Roof technology in the United States. The very good example of how Green Roof technology can be beautifully design is on top of Chicago’s City Hall. The 20,300 feet Green Roof Garden was installed in 2001, as part of Mayor Daley’s Urban Heat Island Initiative.
The Urban Heat Island Effect describes the higher overall temperatures caused by heat trapped and given off by pavement and buildings in dense urban environments. When compared to an adjacent normal roof, City Hall’s green roof was nearly 100 degrees lower, and contributed to $5,000 in annual energy cost reduction, in addition to improving air quality and reducing storm water runoff. The three systems integrated into the design: Extensive, semi-intensive, and Intensive green roofs. Soils were fabricated using lightweight soil mixture guidelines developed in Germany over the past 20 years.
The rooftop is not normally accessible to the public; it is visually accessible from 33 taller buildings in the area. The design form is intended to be read from these various vantage points. The plantings are organized in a sunburst pattern, which respects the symmetry of the historic City Hall and provides a format for arranging groups of plants over the three different roof systems. Though green roofs are typically planted with only sedums and low grasses, the planting palette has been expanded significantly to accommodate research related to the viability of over 100 species of plants.
The variety of plants include native prairie and woodland grasses and forbs, hardy ornamental perennials and grasses, several species of native and ornamental shrubs, and two varieties of trees. Plants are organized by bloom color. As the season progresses from spring through fall, plants bloom across the sunburst pattern. The radiating bands of floral color are segregated by similar bands of grasses. The long bands provide opportunities for the same plant material to be applied over various depths of soil, ranges of slope, and drainage patterns. .