Occupants' behavior can significantly affect building performance, in particular in massive institutional buildings occupied by a wide variety of users. This work aims at highlighting the importance of peers' personal attitudes in determining building thermal-energy, lighting performance, and openings' schedule. A university building located in central Italy was selected. Different rooms with equivalent end-use, geometry, exposure, construction characteristics, occupancy, and appliances were considered. Occupants could be considered as peers, since they carry out the same job and schedule and have the same education and age. Nevertheless, they presented different attitudes and thermal perception, therefore producing different energy need. In order to assess peers' behavior, office rooms were continuously monitored in terms of indoor visual-thermal comfort parameters, electricity consumption, and door/window opening rate in spring, summer, and winter conditions. Occupants' attitudes were compared by considering also the outdoor climate conditions. Results demonstrated that occupants' individual behavior represented a key variable affecting building management of large buildings even if the occupants can be theoretically assumed to be "peers". Significant discrepancies were found between the monitored rooms, demonstrating that typical peers do not behave the same at all, but require differential energy needs that should be considered while predicting thermal-energy and lighting behavior of massive institutional buildings. (C) 2016 Elsevier B.V. All rights reserved.