## 3 Discussion on Results
### Regulatory Requirements and Compliance  
Regarding Spanish Regulations on energy saving and compliance when it comes to building renovation, the CTE DB-HE 2019 [22] sets a global energy consumption limitation (non-renewable consumption of primary energy (C\({}_{\text{ep,nren}}\)) and primary energy total consumption (C\({}_{\text{ep,tot}}\))) when there are interventions in over 25% of thermal envelope, as well as in thermal installations. Specifically, within the climate zone corresponding to the city of Valencia, the regulatory limit value established for the C\({}_{\text{ep,nren}}\) is 55 kWh/m2 per year, and 80 kWh/m2 per year for the C\({}_{\text{ep,tot}}\). In the case of the school buildings studied, the C\({}_{\text{ep,nren}}\) value in the initial state of type A buildings (L0) is 351.3 kWh/m2 per year, 256.9 kWh/m2 per year for type B buildings and 192.1 kWh/m2 per year for type C buildings. The greatest reduction in energy consumption would be obtained through the set of measures L3-WFR. In particular, this set of measures would allow the C\({}_{\text{ep,nren}}\) values to be 207.6 kWh/m2 per year for type A buildings, 183.1 kWh/m2 per year for type B and 116.3 kWh/m2 per year for type C.  
Regarding C\({}_{\text{ep,tot}}\), its value in the initial state for (L0) type A buildings is 425.7 kWh/m2 per year, 311.3 kWh/m2 per year for type B and 205.3 kWh/m2 per year for type C. The set of measures L3-WFR would allow C\({}_{\text{ep,tot}}\) values to be reduced in 251.6 kWh/m2 per year for type A buildings, 221.9 kWh/m2 per year for type B and 128.8 kWh/m2 per year for type C.  
As mentioned above, this study is focused on the renovation of thermal envelope elements, so this limitation is not mandatory. However, it should be considered in the case of performing in facilities. Below, the study analyses the compliance with requirements on transmittance of thermal envelope elements. In any intervention on thermal envelope, every single element renovated must meet requirements on transmittance set by regulations, for example, in the case of window replacement. These values partly correspond to those set for level L2 in Table 2. Level L1, as indicated in Section 2, does not meet the CTE DB-HE 2019 regulation. Particularly, for major renovations over 25% of thermal envelope, the standard also sets a global heat transmission ratio (K). This depends on the climate zone where buildings are located and their compactness. According to the CTE DB HE, the K coefficient indicates the average value of heat transfer ratio for heat exchange surface of the thermal envelope (A\({}_{\text{int}}\)). As shown in Table 9, the K\({}_{\text{lim}}\) level set in the regulations is reached only by implementing one set of measures (L3-WFR) in type C buildings. Consequently, to reduce global ratio of the sets of measures proposed, it is necessary to minimise transmittance, that is, by setting more restrictive energy demand levels in facades (F), roofs (R) and windows (W). Another way to minimise building's energy demand is by performing in other elements, such as interior partitions and floors in contact with unheated rooms. This is not always technically or economically feasible. In view of this situation, legislation provides for the fact that occasionally it is not possible to reach the level of benefit generally established. In these cases, some solutions may be adopted to achieve the highest level of adequacy. This is possible, as long as they are buildings with recognised historical or architectural value, when other solutions are not technically or economically feasible, or solutions involve substantial changes in elements of thermal envelope, or in thermal facilities without initial intervention. For this study, type A and B school buildings could benefit from this flexibility criterion included in the standard, provided that measures implemented are close to limit values.