## 3 Results
### Smart Roof Solutions' Assessment
#### 3.2.1 Green Roof Technology  
In the district analyzed, 64,712 m\({}^{2}\) of roofs were identified as potential green roofs. Referring to Equation (3), the energy savings for heating and cooling seasons were quantified for a district in  
Figure 6: District of Turin with a dimension of 1 km\({}^{2}\): (**a**) Building block classification according to three classes of air quality conditions (green, good; yellow, acceptable, red, bad) [23]; (**b**) analysis of roof potential and feasibility of smart solutions: Green, high-reflectance, and solar roofs.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Rooof Solutions**} & \multirow{2}{*}{**No Buildings**} & \multirow{2}{*}{**Height\({}_{\text{avg}}\) (m)**} & \multicolumn{2}{c}{**Potential Roof Area**} & \multirow{2}{*}{**Slope\({}_{\text{avg}}\) (\({}^{\circ}\))**} \\  & & & **(m\({}^{2}\))** & \\ \hline Green roof & 110 & 13.6 & 64,712 & 0 \\ High reflectance roof & 417 & 3.6 & 44,956 & 9 \\ Solar roof & 570 & 19.3 & 172,749 & 36 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Buildings’ characteristics.  
Turin. In this scenario, potential roofs were renovated using green roof technologies. The thermal transmittance with green technologies is equal to 0.24 W/m\({}^{2}\)/K (according to Italian Decree 26/6/2015) and the solar absorptance of a green roof surface is 0.87 [48; 56]. The energy savings after the installation of green roofs was equal to 5669 MWh/year, which corresponds to 8.4% of space heating consumptions of residential buildings. The energy savings during cooling season was equal to 662 MWh/year. Figure 7 describes the energy savings at block-of-building scale, distinguishing heating and cooling seasons.  
Thermal conditions were investigated using some parameters calculated at block-of-building scale from satellite images (Section 2.1). These parameters are the _NDVI_ and the _LST_ and allow us to describe the UHI effect and the local-climate characteristics of the urban environment. An analysis at blocks-of-building scale was made, and Figure 8a shows the variation of _LST_ before and after the installation of green roof technologies. According to the literature review [34; 35], the _LST_ and the air temperature tend to decrease more or less rapidly as the green areas increase, depending also on the type of urban morphology. Increasing the green roofs' areas of 64,712 m\({}^{2}\), on average, the _LST_ in the district tends to decrease by 1 \({}^{\circ}\)C (Figure 8b).  
Figure 8: Green roofs’ potential assessment at block-of-building scale: (**a**) Thermal condition assessment, Land Surface Temperature (_LST_) variation before and after the installation of green roof technologies; (**b**) correlation between the _LST_ variation and the quota of green roof area.  
Figure 7: Green roofs’ potential assessment at block-of-building scale: (**a**) Heating and (**b**) cooling primary energy savings in MWh/year.  
The feasibility of green roof technology was assessed considering requirements the Ministerial Decree 26/06/2015. The roofs' albedo in the district analyzed varied between 0.05 and 0.26 (for a few buildings, mainly industrial, the albedo was around 0.33) [23]. After retrofit measures with green roofs, the roof albedo criterion was respected due to the installation of passive cooling technology.