The cost-benefit analysis for vertical greening systems in Taiwan

Related studies have confirmed that there are many benefits of vertical greening to the environment. However, whether the vertical greening system (VGS) is under sustainable development economically is yet to be further reviewed. In this study, we evaluated the worthiness of long-term investment in VGS through Cost-Benefit Analysis (CBA) to provide information for reference in future green vertical systems development and promotion. This study conducted a literature review and analysis, provider interview, and CBA. First, based on the widely accepted VGS types, the existing vertical green products in Taiwan were divided into 5 systems according to their construction methods. Respect to the items evaluated in CBA, this study reviewed the studies that aimed to quantify the benefits of VGS and related CBA study for VGS. In terms of cost estimation, this calculated installation, maintenance and updating costs. The VGS benefits demonstrated by the studies were further divided into personal and social aspects. For personal aspect, the benefits terms calculated included building energy saving and wall life extension. For social aspect, the benefits terms calculated included air pollution purification, carbon reduction, and carbon sequestration. We evaluated the economy of the VGSs through three indicators: the net present value (NPV), the benefit-cost ratio (BCR), and the payback period (PBP). The study results showed that most of the 5 VGSs were not profitable. Only direct vertical greening system can produce positive profits, with a payback period of 8 years. For the 5 VGSs, the produced benefits for personal aspect were larger than that for the social aspect. Since most of the demonstrated benefits of VGS concentrated in energy saving and carbon reduction, the benefits of VGSs toward environmental aesthetics, real estate value, etc. were still rare and could not be adopted in this study. Compared to the high costs, the profits of VGS were quite low in this situation. In order to cover more comprehensive benefits of VGS and derive a more reasonable CBA value, the future studies are suggested to address other benefits of VGS. In addition, providing a tax deduction, incentive and reward might stimulate the construction willingness and increase the benefit value of VGS. Respect to the high cost of VGS, this study suggested considering how to cost down while developing a new product.