## 2 Background  
In the context of the existing literature related to the analysis of the economic benefits associated with energy efficiency interventions, several researches investigated the effects of these on the real estate market. In particular, these studies concerned the examination of the relationship between the increase in energy performance deriving from an energy improvement project and the property value differential [23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34]. With reference to different geographical contexts, the Authors have analyzed the economic returns to energy-efficient investments in the real estate market by outlying the benefits derived from energy retrofitting for the existing buildings, in line with the goal of developing sustainable cities. It should be outlined that the present analysis is also focused on the evaluation of the effects of \"generic\" renovation interventions on residential market--in terms of increase in the selling prices--thus including in the category of building renovation interventions those of energy requalification and assuming that an ordinary restructuring operation also concerns technological systems refurbishment (electrical, water, heating, sewage, etc. ), fixtures replacement, and insulation coating installation, aimed at improving the energy efficiency of the building. In general terms, the energy retrofit of existing buildings represents a complex process involving various decision-making issues, relating not only to technical and technological aspects but also to environmental, social, and cultural ones [35]. The use of new construction materials and techniques and the implementation of innovative regulatory policies aimed at promoting the energy efficiency [36] of the existing assets have allowed one to raise awareness on the importance of the buildings energy aspects among all the operators involved: planners, designers, experts, and users [37]. In this sense, for example, [PERSON] et al. [38] have investigated the effect of Energy Performance Certificate (EPC) ratings on residential prices in Wales, by attesting to significant positive price premiums for dwellings in EPC bands A/B (+12.8%) and C (+3.5%) compared to houses in band D, whereas lower discounts have been estimated for residential properties in bands E (\(-3.6\%\)) and F (\(-6.5\%\)). The existing literature related to the analysis of the energy efficiency investment measures also concerns the assessment of the empirical relevance of various barriers to their diffusion [39]; the identification of bottlenecks that hamper energy-saving investments and the definition of proposals to overcome them [40]; and the analysis of the effectiveness of different strategies for the energy retrofit, taking into account their cost efficiencies [41]. The number of studies dealing with the effects of investments in energy efficiency on the residential value is currently limited as most of the recent literature has focused on commercial properties and has analyzed the effects of energy certifications [42; 43; 44], attesting to significant impacts of certification on office properties prices and rents. According to a report developed by International Energy Agency (IEA) [45], the market operators are willing to pay a higher price to rent or to buy a property with better energy performance. [PERSON] and [PERSON] in 1983 [46] and subsequently [PERSON] and [PERSON] in 1989 [47] have carried out analyses aimed at evaluating the influence of energy bills savings on selling prices, concluding that a decrease of 1 dollar on energy bills is capitalized in increases of the residential selling price in a range between 11.63 and 20.73 dollars per m\({}^{2}\). Starting from data detected by the American Housing Survey from 1991 to 1996 in 30 metropolitan areas, in the research developed by [PERSON] and [PERSON] [48], multiple regressions have been implemented to analyze the impact of billing expenses on housing prices, by demonstrating a relevant real estate market appreciation for energy cost savings.