The paper deals with the design procedures for the refurbishment, seismic improvement and reuse of a class of historical buildings defined ordinary since they have an intermediate relevance within the cultural heritage of a country. The procedures include the basic knowledge, the assessment methods, the design works aimed at defining appropriate cost-effective technologies and methods for the structural and seismic retrofitting. The research is carried out with reference to an emblematic study-case concerning the reuse of the complex of San Benedetto Novello in Perugia as a center for artistic and cultural activities. The complex includes architectural elements attributed to Gaelazzo Alessi and is nowadays partially occupied by offices. The study provides for the evaluation of the structure safety considering both the global and local level with reference to the performance levels expected at the different limit states. The works for seismic improvement have been designed respecting the peculiarities of the ecclesiastical complex and allowing the performances required by the new functions. Special focus is given to the use of innovative restoring and strengthening technologies allowing for works characterized by cost effectiveness and contained invasiveness.