In the present paper, additions in structural steelwork are utilised for giving new lives to old buildings in regions characterized by medium/high seismic hazard. Two models are here proposed, i.e.: vertical addition for masonry buildings and lateral addition for r.c. buildings. For the model of vertical addition, the connection between the masonry and steel structures is realised by means of an intermediate isolation system (IIS). For the model of lateral addition, an exoskeleton (EXO) is rigidly connected to the existing building. Two buildings, representative of the heterogeneous Italian building stock, are selected as case studies. Parametric analyses are firstly performed on lumped mass models to explore the feasibility and effectiveness of the IIS and EXO systems in reducing the seismic response of the case studies; then, once selected the actual configurations of the new additions, more refined 3D FE models are adopted for the detailed analysis of the two solutions.