## 5 Conclusions  
A POS has been obtained for a case study building located in a mild climate in the Med region of Spain. Primary energy savings for the POS are very high, between 53.8% and 57.2%, with a 30-year life cycle cost between 183.5 and 197.9 \(\upxi\)/m\({}^{2}\). The life cycle cost of the current building (275 \(\upxi\)/m\({}^{2}\) in its pre-renovation situation) has been reduced considerably, between 28% and 33%. Since the LCC includes the initial investment and the operating and maintenance costs, it can be said that all the measures of the POS are very interesting from an economic point of view. The investment cost to implement the POS is between 42.6 \(\upxi\)/m\({}^{2}\) and 55.3 \(\upxi\)/m\({}^{2}\). These costs have been evaluated according to the prices reported in Section 3.2, obtained from the database of construction prices in the Valencian Community [36], the region where the pilot building is located. Thus, the validity of the results is circumscribed to the same building typology, climatic zone and cost of renovation measures and energy. It should be noted that with the same initial investment, several renovation solutions can be found, many of which have a higher life cycle cost and energy consumption than those found in the POS. Likewise, there are solutions with the same primary energy consumption as the optimal one but with a much higher initial investment. Specifically, there is one renovation alternative with an energy consumption of 36.87 kWh/m\({}^{2}\), a 30-year LCC of 321.47 \(\upxi\)/m\({}^{2}\) and an initial investment of \(\upxi\) 179.8/m\({}^{2}\). Note that due to the optimization performed, the investment cost is reduced by 76.3%. In other words, the same result is achieved in terms of energy consumption, but with an investment 4.22 times lower. Therefore, before renovating a building, it is necessary to be clear about the savings objectives to be achieved, the improvement measures available and their cost before deciding on the best combination. The combination of measures is more effective than the individualized application of each one and it is necessary to make calculations, or follow some indications, to optimize the intervention in terms of investment. The optimal solution or the POS obtained can be compared with other previous studies, specifically with the study by [PERSON] et al. [16]. Although the use of the buildings is different, remarkably similar values are observed in terms of payback period since the optimized measures have a cost proportional to the savings they provide. If the compare the POS of the pilot apartment building to the POS obtained for generic reference buildings, we observe that the latter lead very well towards the optimum, although it would be necessary in the long term to have more powerful tools or pre-calculated cases that allow engineers and architects to take a decision that optimizes the life cycle cost of the building and its systems. In the future, more research should focus on step-by-step renovations because some users, especially private owners, do not carry out renovations in a single step. When a one-moment-in-time optimal renovation is split into different stages, it is very important to define which measures should be implemented in each step as this order has repercussions on the LCC, the payback and of course in the initial investment of that step.