تجزیه و تحلیل هزینه - منفعت اجتماعی احتمالی برای بام های سبز: رویکرد چرخه حیات
|کد مقاله||سال انتشار||تعداد صفحات مقاله انگلیسی||ترجمه فارسی|
|23518||2012||11 صفحه PDF||سفارش دهید|
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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Building and Environment, Volume 58, December 2012, Pages 152–162
Green roofs have been used as an environmentally friendly product for many centuries and considered as a sustainable construction practice. Economic and environmental benefits of green roofs are already proven by many researchers. However, a lifecycle net benefit-cost analysis, with the social dimension, is still missing. Sustainable development requires quantitative estimates of the costs and benefits of current green technologies to encourage their use. This paper is based on an extensive literature review in multiple fields and reasonable assumptions for unavailable data. The Net Present Value (NPV) per unit of area of a green roof was assessed by considering the social-cost benefits that green roofs generate over their lifecycle. Two main types of green roofs – i.e. extensive and intensive – were analyzed. Additionally, an experimental extensive green roof, which replaced roof layers with construction and demolition waste (C&D), was assessed. A probabilistic analysis was performed to estimate the personal and social NPV and payback period of green roofs. Additionally, a sensitivity analysis was also conducted. The analysis demonstrated that green roofs are short-term investments in terms of net returns. In general, installing green roofs is a low risk investment. Furthermore, the probability of profits out of this technology is much higher than the potential financial losses. It is evident that the inclusion of social costs and benefits of green roofs improves their value.
The construction industry is responsible to satisfy human development needs, but it is, in general, destroying the environment simultaneously. It is recognized that construction practices are one of the major contributors of environmental problems, particularly due to the utilization of non-renewable materials . The United States Green Building Council (USGBC) estimated that commercial and residential buildings release 30% of the greenhouse gases and consumes 65% of electricity in USA . To reduce the damage created by the construction industry, environmentally friendly practices that contributes in energy saving, reduction of emissions, and re-use and recycle of materials have been introduced . Green roofs have been used as an environmentally friendly product to encourage sustainable construction. Their popularity is increasing due to their multiple environmental benefits; nevertheless, their cost and weight disadvantages have been a challenge to the industry  and . Green roofs are classified as intensive and extensive according to their purpose and characteristics  and . Intensive roofs are associated with roof gardens; need a reasonable depth of soil and require constant maintenance . Extensive roofs have a relatively thin layer of soil, and are designed to be virtually self-sustaining, therefore require low maintenance . Environmental benefits of a green roof vary with the type of green roof; however, all types provide positive environmental benefits. Installation cost, maintenance, and construction time depend on the type of the green roof. Compared to the intensive type, extensive green roofs are lighter and require lower maintenance cost . However, other benefits such as retention and delay of storm water, temperature control, and agricultural space effects can also be relatively lower. Environmental and operational social-cost benefits of vegetated roofs are several and can be listed as; reduction of energy demand for heating and cooling, mitigation of urban heat island effect, reduction and delay of storm water runoff, improvement in air quality, replacement of displaced landscape, enhancement of biodiversity, provision of recreational and agricultural spaces, and insulation of a building for sound , , , , ,  and . There are different green roof systems available in the market to cater for different weather conditions and user expectations. Usually, green roofs have, from bottom to top, a root barrier, drainage, filter, growing medium, and vegetation ,  and . Manufacturers use worldwide-produced polymers, like low-density polyethylene (LDPE) and polypropylene (PP), due to their easy installation, high strength, durability and low production cost . Generally, recycled LDPE is used to manufacture the root barrier, and recycled PP is used to manufacture the water retention and drainage layers. These plastics improve the performance of green roof systems, reduce cost and overall weight of the system; however, their use as green roof layers has a socio-environmental cost. Green roofs take on average 25 years to balance the pollution released to air due to the production process of polymers . Thereby, reusing waste materials can reduce the green footprint of vegetative roofs. Responsible construction management requires quantitative estimates of costs and benefits of the alternative uses of the environment . Kosareo and Ries , Clark et al. , and Carter and Keeler  have proven the economic advantages of green roofs. However, a lifecycle benefit-cost value representing a unit of area of a green roof is still not available. This paper focuses on filling the gap with best available data based on reasonable assumptions. Data related to lifecycle social-cost benefits of green roofs is extremely rare and mostly qualitative (difficult to quantify). The analysis presented in this paper is based on an extensive literature review in multiple fields, such as forestry, engineering, and plant biology. This paper estimates the present value of a green roof, by assigning a monetary value to the social-cost benefits that standard commercial green roofs generate, over their lifecycle. Furthermore, results of commercial green roofs are compared with the Net Present Value (NPV) of an extensive, construction and demolition (C&D) waste based, experimental green roof. A probabilistic analysis was performed to estimate personal and societal costs/benefits. Additionally, a sensitivity analysis was conducted to calculate the payback period.
نتیجه گیری انگلیسی
Green roofs provide personal and social benefits. The probabilistic NPV analysis determined that there is a low financial risk for installing any green roof type. Additionally, from a personal perspective, the potential profit of an intensive green roof is much higher than its potential losses. Vegetative roofs are a personal investment. However, over the lifecycle of these roofs, both personal and social sectors derive economic benefits. In fact, when social costs and benefits are considered in the NPV estimation, the profitability of the investment is higher. Installing green roofs would be an even more attractive business, if social benefits were partially transferred to investors. The governments should promote green roof construction by reducing insurance premiums and partially subsidizing maintenance costs. These incentives will enhance green roof construction on new and existing buildings with added social environmental benefits. This analysis demonstrated the financial benefits of re-using waste materials in green roof construction. The main social costs of green roofs were found to be in the manufacturing and decommission phases of their lifecycle. Furthermore, green roofs should be seen as a part of a suite of environmentally friendly construction practices. Green buildings must be considered as economically feasible construction systems. The economic feasibility of every possible element is important to increase the market value of green technologies. Innovation and further research is required to decrease the carbon footprint of green technologies over their lifecycle. As urbanization increases, it is critical to find a balance between human development requirements and environmental concerns.