Clark Corrie, Adriaens Peter, Talbot F Brian
Department of Civil and Environmental Engineering, College of Engineering, and Department of Operations and Management Sciences, Ross School of Business, University of Michigan, Ann Arbor, MI 48109-2125, USA.
Environ Sci Technol. 2008 Mar 15;42(6):2155-61. doi: 10.1021/es0706652.
Green (vegetated) roofs have gained global acceptance as a technologythat has the potential to help mitigate the multifaceted, complex environmental problems of urban centers. While policies that encourage green roofs exist atthe local and regional level, installation costs remain at a premium and deter investment in this technology. The objective of this paper is to quantitatively integrate the range of stormwater, energy, and air pollution benefits of green roofs into an economic model that captures the building-specific scale. Currently, green roofs are primarily valued on increased roof longevity, reduced stormwater runoff, and decreased building energy consumption. Proper valuation of these benefits can reduce the present value of a green roof if investors look beyond the upfront capital costs. Net present value (NPV) analysis comparing a conventional roof system to an extensive green roof system demonstrates that at the end of the green roof lifetime the NPV for the green roof is between 20.3 and 25.2% less than the NPV for the conventional roof over 40 years. The additional upfront investment is recovered at the time when a conventional roof would be replaced. Increasing evidence suggests that green roofs may play a significant role in urban air quality improvement For example, uptake of N0x is estimated to range from $1683 to $6383 per metric ton of NOx reduction. These benefits were included in this study, and results translate to an annual benefit of $895-3392 for a 2000 square meter vegetated roof. Improved air quality leads to a mean NPV for the green roof that is 24.5-40.2% less than the mean conventional roof NPV. Through innovative policies, the inclusion of air pollution mitigation and the reduction of municipal stormwater infrastructure costs in economic valuation of environmental benefits of green roofs can reduce the cost gap that currently hinders U.S. investment in green roof technology.
绿色（植被）屋顶作为一种有潜力帮助缓解城市中心多方面、复杂环境问题的技术，已获得全球认可。虽然地方和区域层面存在鼓励绿色屋顶的政策，但安装成本仍然高昂，阻碍了对该技术的投资。本文的目的是将绿色屋顶在雨水、能源和空气污染方面的一系列益处定量整合到一个考虑建筑特定规模的经济模型中。目前，绿色屋顶的价值主要体现在延长屋顶使用寿命、减少雨水径流以及降低建筑能耗上。如果投资者超越前期资本成本来看待这些益处，对其进行恰当估值可以降低绿色屋顶的现值。将传统屋顶系统与广泛的绿色屋顶系统进行净现值（NPV）分析表明，在绿色屋顶使用寿命结束时，绿色屋顶的NPV在40年内比传统屋顶的NPV低20.3%至25.2%。额外的前期投资在传统屋顶需要更换时得以收回。越来越多的证据表明，绿色屋顶可能在改善城市空气质量方面发挥重要作用。例如，估计每减少一公吨氮氧化物，绿色屋顶对氮氧化物的吸收量价值在1683美元至6383美元之间。本研究纳入了这些益处，结果表明对于一个2000平方米的植被屋顶，每年的益处为895美元至3392美元。空气质量的改善使得绿色屋顶的平均NPV比传统屋顶的平均NPV低24.5%至40.2%。通过创新政策，在绿色屋顶环境效益的经济评估中纳入减轻空气污染和降低市政雨水基础设施成本，可以缩小目前阻碍美国对绿色屋顶技术投资的成本差距。
