Evaluating the economic sustainability of a vertical greening system: A Cost-Benefit Analysis of a pilot project in mediterranean area

The growing diffusion of vertical green systems has led to the development of new systems and technological solutions which can improve the quality of urban environments. The present research evaluates the economic sustainability of a vertical greening system (VGS) installed on an office building in Genoa (Italy) through a Cost-Benefit Analysis (CBA). The benefits deriving from the installation of VGS are compared with the costs. The economic benefits considered are related to the economic effects of energy savings (for air conditioning), with values deriving from field studies and monitoring activities, biomass production, estimated according to the material produced by annual maintenance works (pruning), and property value. The latter is estimated thanks to the involvement, by means of a specific survey, of real estate agents working in the city of Genoa. Results show that a VGS can be economically sustainable when a tax reduction on installation costs is considered; in this case, the Net Present Value and the Internal Rate of Return are positive and the Pay Back Period is lower than the life span of VGS. A relevant contribution is also determined by the energy saving for building summer conditioning due to the reduction of the external air temperature. A Monte Carlo simulation allows verifying the reliability of the results obtained for the economically sustainable scenarios. A Sensitivity Analysis on the main variables underlines the relevance of the design phase in order to optimize the choice of materials and technological solutions reducing installation and maintenance costs.