The design and selection of a retrofitting solution can be carried out through performance-based methods (according to constructive materials behaviour, hygrothermal and occupants’ behaviour or climatic conditions) as an alternative to the deem-to-satisfy approach. The future likelihood of saturated conditions in masonry building fabrics is increased by the consequences of climatic changes, enhancing the need of selecting adequate solutions for buildings retrofitting. As it was intended to propose the optimal solutions for the preservation of a Portuguese convent, major issues such as the high level of relative humidity inside the building and the leaching phenomenon of the mortar joints between bricks masonry were taken into account as a potential degradation causes. In situ inspection was made together with the analysis of the existing documentation regarding the building. The selection of the best retrofitting measures was supported by innovative leaching and hygrothermal risk analyses using probabilistic approaches. The probability of leaching of the mortar joints is minimised if NHL5 mortars are used for re-pointing when compared to NHL2 or NHL3.5 mortars. Regarding the hygrothermal performance of the building, indoor comfort increases 10% by increasing the Moisture Buffering Value of the indoor surface using eco-efficient earth plasters.