A system for closing openings in a building comprises: at least one structural frame having at least two lateral uprights (11a) and two end cross members, coupled to form a perimetral structure that delimits a space, at least one infill element associated to the structural frame at a front thereof, for closing the space delimited by the perimetral structure, at least one longitudinally extending covering element (21b), configured for being mounted on the structural frame at a back thereof, a magnetic-coupling arrangement (24, 28), for constraining in a magnetic way the at least one covering element (21a) in at least one first region of an upright (11a) or a cross member of the structural frame.