# Optimization of Inspection Period in Natural Stone Claddings
## 5 Conclusions  
In this study, a multi-objective optimization procedure is used to schedule inspection interventions on natural stone claddings. This work intends to understand whether there is an optimal time interval for performing the inspections, considering the several conflicts that the building owners/managers are subjected to. In this case study, the conflicting objectives considered are minimization of the service life cycle costs in terms of maintenance, maximization of the efficiency index of the maintenance plan, maximization of the service life, and minimization of the total number of replacements over the time horizon.  
From the results, two main conclusions can be drawn. Firstly, it is advantageous to implement maintenance strategies with more maintenance activities (strategies that consider preventive interventions). For example, if the most advantageous maintenance strategies are compared, the consideration of maintenance strategies with more activities, although leading to higher maintenance costs, has a higher impact on the improvement of NSC, promoting its durability, protecting the environment, reducing the risks for society, and improving the aesthetic perception and comfort of the cities. Secondly, the time intervals between inspections recommended in the literature are conservative. In the literature, the recommended inspection period for NSC ranges from 2 to 8 years. This study shows that the inspection period can be increased to 11 to 15 years. The results reveal that a cost-saving of 36-58% can be achieved if the inspection period is increased, with a lower impact on the aesthetic appearance (less than 2%).  
Finally, it should be stressed that multi-objective optimization procedures are simply a tool to help decision-makers to make more rational and informed decisions. In the end, the selection of the best alternative is always performed by the building owners/managers and depends on their budgets, demands, and expectations. The main advantage of the multi-objective optimization procedures relies on the fact that it is not a closed methodology. As future research, this methodology can be used to analyze other maintenance strategies--in terms of the type of actions, the minimum requirements, or the environmental context, allowing considering different conflicting parameters--and applied to other buildings' constructive solutions or even the building as a whole.  
**Author Contributions:** Conceptualization, C.F.; methodology, C.F.; formal analysis, C.F.; investigation, C.F., A.S., J.d.B., I.S.D., I.F.-C.; writing--original draft preparation, C.F.; writing--review and editing, A.S., J.d.B., I.S.D., I.F.-C. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by FCT (Portuguese Foundation for Science and Technology) through the project BestMaintenance-LowerRisks (PTDC/ECI-CON/29286/2017).  
**Acknowledgments:** The authors gratefully acknowledge the support of the CERIS Research Institute, Instituto Superior Tecnico, Universidade de Lisboa.  
**Conflicts of Interest:** The authors declare no conflict of interest.