## 4 Results and Discussion
### General Application of the Methodology and Obtaining the Optimal Solution Package
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Package** & **Facade** & **Roof** & **Window** & **Door** & **Slab** & \
\begin{tabular}{c} **Thermal** \\ **Bridge** \\ \end{tabular} & **Ventilation** & **Airtightness** &
\begin{tabular}{c} **Night** \\ **Ventilation** \\ \end{tabular} & **DHW** \\ \hline
**1** & **7** & **5** & **3** & **3** & **3** & **1** & **2** & **2** & **2** \\ \hline
2 & 5 & 2 & 7 & 7 & 3 & 2 & 1 & 2 & 1 & 2 \\
5 & 3 & 4 & 2 & 1 & 3 & 3 & 1 & 1 & 1 & 2 \\
7 & 5 & 3 & 5 & 1 & 3 & 3 & 2 & 2 & 1 & 2 \\
8 & 7 & 2 & 4 & 3 & 3 & 2 & 1 & 2 & 2 & 2 \\
9 & 7 & 3 & 5 & 2 & 3 & 2 & 1 & 1 & 1 & 2 \\
10 & 7 & 4 & 3 & 1 & 3 & 3 & 2 & 1 & 1 & 2 \\
11 & 5 & 3 & 5 & 1 & 3 & 2 & 1 & 2 & 2 & 2 \\
12 & 7 & 7 & 4 & 3 & 3 & 2 & 1 & 2 & 2 & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Packages of Optimal Solutions (POSs). Figure 7: Life cycle cost (LCC) vs. primary energy consumption for 2441 building renovation alternatives. As mentioned, the goal of this study is to find the combination of renovation measures with the best balance in terms of LCC and its impact on energy savings. Table 5 shows the 12 selected packages of renovation measures, and the optimal combination, this is the one that minimized the LCC, has been highlighted in green. The facade, roof, windows, doors, slabs, thermal bridges, ventilation, airtightness, night ventilation and DHW are the areas considered in this evaluation study as the ones that can guarantee that the building is upgraded to NZEB condition. The most common solution for facades was an ETIC system, solution number 7, which guaranteed the continuous insulation of the vertical elements of the envelope, keeping under control the thermal bridges caused by the slab edges on each story. In addition, this solution provided an optimal situation of the thermal mass inside the building, allowing for a high level of energy storage in the building structure. The roof evaluation showed that green roofing (roof number 5) was an option to bear in mind when specifying solutions during the design process. There was a diverse range of very suitable solutions for this zone of the building. Even though green roofing did not appear in other packages, it was included in the optimal package due to its insulation characteristics and the benefits that it offered beyond thermal performance and LCC, such as decreases in albedo and heat island effects and the fact that it was a natural system for capturing CO\({}_{2}\). Moreover, the relationship between its construction cost and thermal performance was better than other construction solutions manufactured with inert materials. Due to the mildness of the climate, the thermal performance capacity of the windows could be lower than in colder regions. The optimal solution for windows was number 3, which is in the middle of the specifications table shown in the list. The optimal solution to reduce thermal bridging was number 3. It was the most recurrent in all packages as the cost differences between the three options was trivial, but the thermal performance increased substantially when this option was used; it combined under-slab insulation with the thermal improvement of the opening contour. In 10 solutions out of 12, ventilation was equal to the base rate (one air change per hour), although in most of these cases airtightness was improved to avoid an increase in the air infiltration rate. Thus, the amount invested in improving ventilation was used in other solutions that simulations showed to be more profitable in terms of life cycle cost, such as improving the thermal transmittance of the elements of the envelope. This was motivated by:  
* the mildness of the climate. In other locations with colder outdoor temperatures the solution could differ;
* the price of the ventilation system in relation to the price of other renovation measures. Regarding airtightness, the optimum solution was number 2, which only focused on solving air infiltration problems without incorporating any extra insulation layer into other elements.