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Green Roofs By Adam Friedberg and Jordan O'Brien Green Roof Life-cycle Assessment Insights from cost-benefit analysis of green roofs versus conventional roofs he financial decision whether to install a green roof should be considered on a case-by-case basis as the variability in structure, municipality, ownership, tenant, investment, technology, climate, installer experience, etc., requires specific attention. In some cases, a life cycle assessment will help decision-makers to better understand the impacts of a green roof over the longterm. With this in mind, a cost-benefit model was developed by the authors to compare the costs of green and conventional roofs — the installation, maintenance and replacement of the roof — with the benefits, savings and value produced by green and conventional roofs, as part of a larger study for the United States General Services Administration (GSA). A green roof is a holistic sustainability strategy that has direct and indirect benefits for multiple stakeholders including developers and owners through installation costs, rental impacts, operational costs, to name a few; municipalities through reduced infrastructure maintenance or replacement costs; the community through improved aesthetics, biodiversity, and/or Stormwater benefits Many municipalities require stormwater management onsite. Compared to a conventional roofing system, which requires additional stormwater management practices such as cisterns, retention ponds, etc., green roofs may be credited toward achieving the regulatory requirements. These best management practice (BMP) stormwater measures also require capital and maintenance costs and, therefore, should be included in an analysis. Municipalities may impose runoff fees to help replace the cost for future citywide stormwater infrastructure required by a Long Term Control Plan, and/or incentivizing future runoff rates such as is the case with the Washington, D.C. utility fee. Such fees may be mitigated through a green roof, depending on the project type. The green roof might also affect public infrastructure, whether the stormwater in a particular city is discharged into a Combined Sewer Overflow (CSO) system, and/or captured and filtered in other ways. Maintenance, such as cleaning and replacement of filters used in the capture/filtration process, must be accounted for. Of course, in an area reliant on a CSO system, the cost of energy and materials required to treat stormwater at the sewage treatment plant will also be borne by the public either through taxes or fees – a point that should be accounted for in any such analysis. Additionally, if future legislation regulates the quality of stormwater discharge, a green roof may improve or degrade the stormwater (depending on limited pollutant) and so, this may also need to be taken into account. Energy benefits The energy cost-savings potential of a NET PRESENT VALUE T green job creation; and building occupants through productivity gains and/or improved psychological and physical wellbeing. To account for these numerous costs and benefits, the analysis reviewed various methodologies and studies of green roof cost-benefit analyses. The most frequent benefits found and studied in the cost-benefit analysis can be found below. While some benefits are quantifiable, others are more qualitative and have limited quantitative evidence. 8 Landscape and Irrigation May/June 2013 www.landscapeirrigation.com