In this study the factorial method proposed in the ISO standard 15686 is used to predict the service life of natural stone wall claddings. This method consists on determining the estimated service life through the multiplication of a reference service life by a set of modifying factors linked to different characteristics of the claddings. The method proposed is based on a survey of the degradation state of 130 stone cladding systems in the region of Lisbon, Portugal. The model is validated by comparing the service life of each case study estimated by the factorial method with that obtained using a graphical method (where the degradation evolution is evaluated based on adjusting degradation curves to the scatter of points corresponding to the cases analysed on site). This comparison allows adjusting the sub-factors in order to optimize their values by minimizing the difference between the two methods in terms of estimated service life.