The subject of our work involved the execution of on-site and laboratory tests to determine the construction method and the mechanical characteristics of the building materials. The building in question consists of a mixed load-bearing structure with load-bearing masonry and reinforced concrete. Core drilling was performed both to determine the quality of the concrete and to verify the structural system of the load-bearing masonry (double/triple walls, layer thickness, etc.). Schmidt-hammer testing was conducted as defined by the National Retrofιtting Regulations for both materials (ΚΑΝΕΠΕ & ΚΑΔΕΤ). Regarding the load-bearing masonry, samples of masonry units and mortar were isolated for determining their mechanical properties at a specialized laboratory. For the reinforced concrete members, cuts/cores were made according to the specifications in National Retrofιtting Regulation to monitor the details of the reinforcement in the columns, beams, and slabs.