## 4 Conclusions  
Through the implementation of optimum-cost methodology, the study aims at identifying the set of improvement measures with optimum intervention cost for each building type studied. It is found that for type A buildings, the most cost-effective intervention would be to renovate facades and roofs (L3-FR), whereas for types B and C, the improvement is only made in facades (L3-F). In all cases, the set of improvement measures that brings buildings closer to nZEB involves performing in all thermal envelope elements with the most restrictive values of thermal transmittance (L3-WFR). All in all, the implementation of cost-optimal sets of improvement measures in 46 schools studied results in an average annual saving of 378,735.34 euros and an annual emission reduction of 720,155.3 kgCO\({}_{2}\). These results show Public Administration in Valencia that the most cost-effective solution is not always the same for all schools, and depends on building typology. This suggests that it is not advisable to renovate the same thermal envelope element simultaneously in all buildings for instance, by renovating windows in all schools. In order to save costs when performing in more than one element or school at the same time, the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & & & \multicolumn{3}{c}{**K (W/m\({}^{2}\)K)**} \\ \hline
**Type of School Building** & **Klim** & **Elements Improved** & **L1** & **L2** & **L3** \\ \hline  & & R & 2.83 & 2.83 & 2.83 \\ Type A & 0.9 & & FR & 2.25 & 2.07 & 1.91 \\  & & WR & 2.44 & 2.19 & 2.13 \\  & & WFR & 1.86 & 1.43 & 1.21 \\ \hline  & & F & 2.27 & 2.18 & 2.09 \\ Type B & 0.85 & & FR & 1.94 & 1.84 & 1.73 \\  & & WFR & 1.90 & 1.62 & 1.46 \\  & & WFR & 1.57 & 1.29 & 1.11 \\ \hline  & & F & 2.31 & 2.21 & 2.14 \\ Type C & 0.86 & & FR & 1.72 & 1.62 & 1.42 \\  & & WFR & 1.82 & 1.54 & 1.50 \\  & & WFR & 1.23 & 0.95 & 0.78 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Global heat transmission ratio K (W/m\({}^{2}\)K). Regulatory requirements according to type of school building, building compactness and climate zone, Klim and ratios obtained for each set of measures and energy demand level. -typeology classification proposed for the sample is suggested to be applied so that the same intervention is replicated for the same typology but not for all schools. The results achieved allow school principals in Valencia to make decisions on carrying out priority renovations in buildings and potential strategies. For example, for those measures with a global cost similar or higher than that in the current state of the building, it is appropriate to perform a deep renovation, including enhancement of thermal envelope and heating and cooling systems, so that the 30-year global cost is reduced. The long-term cost reduction and the quick return of investment of some sets of measures may be a reason for public administrations in Valencia to invest in school renovation. Regarding regulatory requirements, it is shown that an approach to building renovation with the aim of complying with current legislation for new buildings may not be the most cost-effective option. In summary, the cost-optimal methodology applied to the renovation of school buildings studied provides quantitative data on costs and energy saving that can be obtained after implementing specific sets of measures in 46 school buildings in the city of Valencia. All this facilitates to identify, among other data, the initial cost of measures, consumption reduction gains and the return on investment periods. These data can provide public administrations in Valencia with criteria to design long-term intervention plans, which enable available resources to be efficiently invested. Irrespective of the specific results reached, the adaptation of the methodology proposed to a wider scale (regional/national) can help to build support for deciding about the renovation of school buildings and designing long-term renovation strategies. The study can also be expanded to other buildings in the city, as well as other cities or regions.