The seismic safety of the existing built heritage of precast industrial buildings in Italy is a challenge currently faced by both technical community and governmental bodies. However, selecting the proper retrofit interventions for these buildings is a non-standard issue, due to their peculiar behaviour under earthquake action. This paper explores the probabilistic seismic assessment of a prototypal single-story reinforced concrete precast building designed in compliance with past codes and retrofitted according to current regulatory standards in high seismicity zones in Italy. The beneficial effects induced by strengthening local interventions on roof-to-beam and panel-to-structure connections, avoiding economically unviable column jacketing, are addressed by advanced numerical modelling of original and retrofitted configurations analysed via multi-stripe non-linear dynamic analyses. Seismic fragility curves and annual failure rates of exceedance of performance levels regarding usability and collapse are numerically derived to comprehensively quantify the risk mitigation ensured by the proposed interventions.