Economic Benefits

The economic benefits of green roofs are widely discussed in literature over at least a decade [71–73,81–86]. Teotónio et al. [81] explained that di fferent economic evaluations of green roof systems give a high variability of results. Moreover, Teotónio et al. [81] reported that, from a financial perspective, green roofs' investments usually lead to financial losses of 19–50%, given their limited private benefits, whereas, from an economic and socio-environmental perspective, green roofs are mostly identified as interesting investments, leading to gains of 24–40%. Castleton et al. [73] reported that, in terms of whole-life cost analysis, the Net Present Value (*NPV*) of a green roof is 10–14% more expensive than a conventional roof over a 60-year lifetime. Yet, Bianchini et al. [82] explained that a reliable encompassing lifecycle net benefit-cost analysis, or any other calculation systems, should also take into consideration personal costs and benefits, initial construction cost, property value, tax reduction systems in place, storm water retention and avoidance in drainage system, energy reduction (both in terms of cooling and heating), plant longevity benefits, and operational and maintenance costs. Moreover, Sproul et al. [79] demonstrated a considerable variation in the economic value of white, green, and black flat roofs.

Bianchini et al. [82] also stated that:" ... Green roofs provide personal and social benefits ... 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."

Moreover, according to the monitoring activities on the real estate market in Italy, ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development) 'Istituto per la Competitività (I-Com)' and the 'Federazione Italiana degli Agenti Immobiliari Professionisti (FIAIP)' show a strong correlation between the performing energy classes, potentially improved by the greening process of roofs, among other factors, and the trend in the real estate market. The general positive trend in 2019 showed a progressive reduction of buildings sold falling into the poorest energy class (G), which was around 40% for one-room and two-room apartments, 37% for three-room apartments, around 34% of single-family villas, and 24% for villas. Especially for these last two categories of homes, the improvement in the figure compared to the previous year is very positive. The signals coming from the renovated buildings' segmen<sup>t</sup> are also positive, with the percentage of buildings belonging to the best-performing energy classes (A +, A, and B) going from 10% in 2017 to 22% in 2018.
