Unreinforced masonry buildings represent a large portion of the building stock in most historical centres of European countries. In most instances, these constructions are not isolated, but grouped in clustered buildings made up of multiple adjacent structural units erected in continuity one to each other. Since the units interact dynamically under seismic actions, it is impossible to analyse their behaviour disregarding the contribute of the adjacent cells. Moreover, these constructions were erected without any seismic criteria and for this reason, nowadays, their requalification is an urgent need both from structural and energy points of view according to European Directives. In this paper, the vulnerability assessment of a masonry clustered building placed in Timişoara, the most important city in the Romanian Banat region, which is one of the two major seismic areas of the country, is investigated. Firstly, after the main geometrical and structural properties of the construction, dated back to 1900, have been collected, static non – linear analyses are performed obtaining the capacity curves. Subsequently, since the behaviour has appeared inadequate to withstand seismic actions, a retrofit intervention has been hypothesized. Among different and innovative techniques, the choice has been directed towards the use of lightweight metal exoskeletons arranged along the external facades of the aggregate so to create a continuous coating system. It is made up of aluminium alloy extruded profiles, fixed to the masonry walls by chemical anchors, completed with thermo – insulating panels. This innovative system allows simultaneous the improvement of both seismic and energy performances of the construction. Finally, after the envelope system has been dimensioned and applied to the case under study, its benefits and effectiveness have been demonstrated repeating the pushover analyses and comparing the results in terms of seismic safety index, intended as the ratio between capacity and demand PGA, before and after the intervention.