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The Benefits and Challenges of Green Roofs on Public Building

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The Benefits and Challenges of Green Roofs on Public Building The Benefits and Challenges of Green Roofs on Public and Commercial Buildings A Report of the United States General Services Administration MAY 2011 Front cover: Image of the green roof on the United States Department of Transportation Headquarters CONTENTS EXECUTIVE SUMMARY......................................................................................................i 1.0 INTRODUCTION 1.1 Purpose of Study ................................................................................................................................... 1 1.2 Methodology .......................................................................................................................................... 1 1.3 Background to Green Roofs ................................................................................................................... 2 1.4 Cost ...................................................................................................................................................... 8 1.5 Scope of Report .................................................................................................................................... 9 2.0 BENEFITS .........................................................................................................11 2.1 Stormwater Management ......................................................................................................................13 2.2 Biodiversity and Habitat ....................................................................................................................... 25 2.3 Urban Heat Island .................................................................................................................................31 2.4 Energy ................................................................................................................................................ 37 2.5 Urban Agriculture ................................................................................................................................ 43 2.6 Acoustics .............................................................................................................................................47 2.7 Air Quality ............................................................................................................................................51 2.8 Aesthetics and Quality of Life .............................................................................................................. 55 2.9 Job Generation and Economic Development ........................................................................................ 59 2.10 Roof Longevity .................................................................................................................................... 63 3.0 COST BENEFIT ANALYSIS ..................................................................................67 3.1 Purpose .............................................................................................................................................. 67 3.2 Methodology ........................................................................................................................................ 67 3.3 Assumptions ........................................................................................................................................ 68 3.4 Results ................................................................................................................................................ 70 3.5 Discussion............................................................................................................................................74 4.0 CHALLENGES TO GREEN ROOF CONSTRUCTION...................................................77 4.1 Siting and Design ................................................................................................................................ 77 4.2 Installation and Construction ............................................................................................................... 80 4.3 Maintenance and Operation ................................................................................................................. 83 GSA GREEN ROOF BENEFITS AND CHALLENGES TABLE OF CONTENTS TABLE OF CONTENTS GSA GREEN ROOF BENEFITS AND CHALLENGES CONTENTS CONT’D 5.0 RESEARCH AND DATA NEEDS .................................................................................................. 89 5.1 Stormwater Management ..................................................................................................................... 89 5.2 Biodiversity and Habitat ....................................................................................................................... 90 5.3 Urban Heat Island ................................................................................................................................ 90 5.4 Energy ................................................................................................................................................ 91 5.5 Acoustics ............................................................................................................................................ 92 5.6 Urban Agriculture ................................................................................................................................ 92 5.7 Air Quality ........................................................................................................................................... 92 5.8 Job Generation and Economic Development ........................................................................................ 92 5.9 Aesthetics and Quality of Life .............................................................................................................. 92 6.0 CONCLUSION ................................................................................................................................. 95 DEFINITIONS, ABBREVIATIONS AND ACRONYMS .......................................................99 APPENDIX A ................................................................................................................................................105 APPENDIX B ................................................................................................................................................109 BIBLIOGRAPHY ....................................................................................................... 117 REFERENCES .......................................................................................................... 129 GSA GREEN ROOF BENEFITS AND CHALLENGES TABLE OF CONTENTS GSA National Capital Region - United States Census Bureau Headquarters, Suitland, Maryland The facility includes two extensive and intensive green roofs that total 85,000 square feet made accessible through walking paths. EXECUTIVE SUMMARY BACKGROUND costs, benefits, challenges and opportunities of green Cities create remarkable social environments out of roofs, along with an original cost-benefit analysis, what had been untouched natural landscapes. It is discussion of best practices and assessment of further important to understand what is lost in that process research needs. A in-depth analysis of the benefits, as well. Besides being attractive, natural landscapes challenges and opportunities of alternative roofs such absorb and infiltrate stormwater, provide cooling from as conventional roofs or white roofs was beyond the excess heat, offer habitats to a diversity of species, and scope of this report. improve air and water quality. GREEN ROOFS IN THE UNITED STATES The urban hardscape—a term for heavily urbanized Green roofs have been around a long time. Prairie areas with little bare soil—cuts cities off from these homesteaders built sod houses when settling the natural processes and creates problems like water frontier. There have been green roofs on US Government pollution and increased temperatures through the urban buildings and parking structures for nearly a century— heat island. green roofs installed on several federal buildings in the Washington DC region have not been replaced since Green roofs—sometimes referred to as ‘vegetated their installation in the 1930s. Although they have roofs’ or ‘eco-roofs’—consist of a waterproofing been used infrequently for decades, green roofs are membrane, growing medium (soil) and vegetation now being revived and studied for their environmental (plants) overlying a traditional roof. Green roofs can benefits. The growth of green roofs in the US mirrors help mitigate the problems that cities create by bringing their use in other countries, like Germany, where they the natural cooling, water-treatment and air filtration are more commonly seen. properties that vegetated landscapes provide to the urban environment. Architects and planners can use The General Services Administration (GSA) has green roofs to help solve environmental problems by designed and maintained green roofs for decades and bringing nature back to the city in key ways. Green roofs finds them to be economical amenities that make fiscal properly designed, constructed and maintained, are and environmental sense. The GSA currently maintains beneficial socially, environmentally and fiscally. They at least 24 green roofs in 13 cities around the country. are an important tool to increase sustainability and GSA routinely installs green roofs on new and existing biodiversity and decrease energy
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