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<br />Chicago Beats the <br />Heat with Green <br />Techniques <br />(continued) <br /> <br />001651 <br /> <br />seen on so many city buildings. Many taller buildings surround the site, making the project visible <br />to many in the city. Weather centers on both the City Hall and County Hall rooftops have been <br />gathering baseline data on temperature, wind, and rainfall since summer 1999. Local high school <br />students will help monitor the weather centers and use the data for classroom projects. <br /> <br /> <br />Planning the Rooftop Garden <br /> <br />Despite what most people think, a rooftop garden does not have to be extremely heavy and require <br />extra structural support. At City Hall, Jessica Rio noted, "the majority of the rooftop will be <br />ground cover with relatively litde soil, weighing only 20 to 34 pounds per square foot." City Hall's <br />roof will be covered with drought-tolerant plants such as buffalo grass and common blue violet. <br />Most rooftop gardens, including the one on City Hall, will also include islands of semi-intensive <br />plants (see figure below) such as junipers that require 6 to 8 inches of soil, weighing 50 to 90 <br />pounds per square foot. City Hall's landscape plan also includes vines such as American <br />bittersweet, which will climb up the walls of the different levels of the roof. <br /> <br />Gardens on rooftops with adequate structural support can also <br />include trees in large containers. The adequacy of structural <br />support is not an issue for the City Hall building rooftop garden <br />because the original building plans called for another floor that <br />was never built. Taking advantage of this added support, the city <br />will plant trees such as Washington hawthorne and prairie <br />crabapple in two large containers requiring 30 inches of soil each <br />and weighing 80 to 200 pounds per square foot. <br /> <br />Storm Water Savings <br />Plants will be installed on approximately half, or 20,000 square <br />feet, of the City Hall roof. Kimberly Worthington, DOE <br />Engineer, notes that City Hall's rooftop garden "will capture and <br />filter up to a I-inch rainfall." Additional rainfall will drain off the <br />roof into the sewer system. <br /> <br />Chicago has a combined sewer system, treating both wastewater <br />and storm water during a storm event. For now, the city's few <br />demonstration projects will not have a noticeable impact. <br />"However," explains Wonhingon, "if we begin to do several <br />projects around the city, we will see some impact. When taken <br />collectively, these projects will reduce loading on the sewer <br />system. If we can reduce the impact, maybe we can increase the infrastructure's life." Several <br />demonstration projects are planned at public facilities around Chicago. In addition, DOE will <br />soon provide grants to landowners who wish to implement heat-reducing projects. <br /> <br />Gravel <br />Growing Medium, 6-8" <br /> <br /> <br />Filter Material <br />Drainage Layer, 6" <br /> <br />Root Protection Material <br />Protection/Separation Material <br />Waterproof Membrane <br />Insulation Layer <br /> <br />Existing Roof <br /> <br />MARCH 2000, ISSUE #60 <br /> <br />Semi-Intensive Roof System <br />NONPOINT SOURCE NEWS-NOTES <br /> <br />9 <br />