# Experimental Evaluation and Numerical Simulation of the Thermal Performance of a Green Roof
## 4 Conclusions  
A green roof, installed on an actual building, was examined through on-site measurements. Several measuring instruments were applied for monitoring heat transfers phenomena across the green roof, making a comparison with a nearby conventional roof. Due to difficulties modelling the \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Rome**} & \multicolumn{2}{c}{**Manaus**} & \multicolumn{2}{c}{**Abu Dhabi**} & \multicolumn{2}{c}{**Moscow**} \\ \cline{2-9}  & **Heating** & **Cooling** & **Qheat** & **Qcool** & **Qheat** & **Qcool** & **Qheat** & **Qcool** \\ \hline Green roof & 11,388 kWh & 1439 kWh & 0 kWh & 4798 kWh & 379 kWh & 10,597 kWh & 34,529 kWh & 42 kWh \\ \hline Original roof & 14,442 kWh & 2205 kWh & 0 kWh & 7168 kWh & 654 kWh & 14,197 kWh & 42,807 kWh & 113 kWh \\ \hline Variation & \(-21.14\%\) & \(-34.70\%\) & - & \(-33.06\%\) & \(-42.03\%\) & \(-25.36\%\) & \(-19.34\%\) & \(-62.90\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison among heating and cooling energy needs in different climatic conditions. Figure 10: Comparison between annual heating and cooling energy needs. green part of the roof, an equivalent model was generated for obtaining equivalent thermophysical properties to be used in building energy simulation tools. The outcomes of this study conclude that:  
* The comparison between the original and the green roof reveals that the roof-lawn system has a more stable thermal behavior, during both summer and winter seasons;
* Making a comparison between the green and the original roofs U-values, a percentage difference of about \(-55\%\) was highlighted, demonstrating a significant insulating effect of the green roof;
* The roof-lawn system significantly increases the inertial behavior of the roof, generating higher thermal comfort in the indoor environment for occupants;
* The equivalent thermophysical properties were found and verified during summer, middle season and winter, thus demonstrating the effectiveness and the reliability of the assessed values;
* A significant reduction in the energy needs of the building was achieved: when simulating the roof-lawn system compared to the original roof, percentage differences of \(-21.14\%\) and \(-34.70\%\) were obtained for heating and cooling, respectively. Green roofs have a thermal insulation function, known since ancient times. It is therefore true that this kind of systems involve higher initial costs, which can be amortized quickly [7]. Green roofs are also a natural barrier against noise pollution. The green roof can absorb external noise by reducing the reflection of sound. In addition, greenery produces oxygen and captures CO\({}_{2}\) and polluting agents, representing a natural countermeasure against air pollution. Among passive solutions, green roofs represent a sustainable answer, reducing the collateral effect of the Urban Heat Island phenomenon. Future developments will concern the optimization of the structural part of the roof, and designing a stratigraphy able to better work with the overlying roof-lawn. Data curation, C.G. and L.E. ; Formal analysis, C.G. and L.E. ; Methodology, C.G., L.E., F.A. and R.D.L.V. ; Supervision, F.A. and R.D.L.V. ; Writing--original draft, C.G. and L.E. ; Writing--review & editing, F.A. and R.D.L.V. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The authors declare no conflict of interest.