Green Roofs vs. Cool Roofs. Economic evaluation of private and public benefits derived from industrial buildings retrofit in Italian different climate conditions

Extensive green roofs (GR) represent an interesting option for industrial building refurbishment, providing private and social benefits. In Italy, green roof technology is uncommon, because of high installation cost that drives towards more traditional solutions, such as cool roofs (CR). A thorough valuation of green roofs benefits in urban contexts is required to encourage their diffusion. The valuation of private and social performances of GR versus CR has been performed in industrial settlements close to residential areas in the cities of Trieste, Ancona and Palermo, where these cities are characterised by different climate conditions. These case studies have allowed us to explore all the main aspects, both private and social, that affect convenience of adopting a GR compared to a CR. The private cash-flow analysis demonstrates that a private investor has a poor convenience to implement GR rather than CR. On the other side, social cost-benefit analysis shows a positive net present value due to the GR externalities, in particular the aesthetic improvement of industrial settlements perceived by the residents of the surroundings, valuated with their willingness to pay for a diffusion of GRs. The social advantage to adopt a GR compared to a CR let the calculation of the economic incentives amount to promote the spread of GR in the Mediterranean area. The incentive analysed is the reduction of local property tax. This reduction of amount owed by a private investor could be financed with an increase of property tax on residential real estate (Tax Increment Financing), favoured by the aesthetic improvement of industrial settlements. The comparison between private and social performances of a GR versus a C R in three different climate contexts is very interesting to identify the main drivers of private and social GRs' benefit and to calibrate the incentives to favour the diffusion of GR.