The paper illustrates the case study of a tertiary building, entirely used as offices (7 floors and over 12000 m2 of surface), where the façade acoustic insulation D2m,nT,w is the only mandatory requirement basing on D.P.C.M. 05/12/97. The façade varies along the building as its components largely differ one from the other in terms of shapes, sizes of the inner environments, shape factor and type of windows. Basing on onsite measurements referred to some representative rooms, the minimum acoustic requirements according D.P.C.M. 05/12/97 have been evaluated. The good accordance between the measured values and the expected results according to UNI EN ISO 12354-3 standard shows both the reliability of the theorical model and the absence of macroscopic mistakes in the measurement stage. The model was then used to preliminary verify the effectiveness of several acoustic insulation interventions. The presented case study allows further operational considerations about the applicability of the acoustic classification of real estate unit based on the UNI 11367 standard. The predictive model shows that the accomplishment of both the minimum requirements and the maximum acoustic class is possible, even for a building of historical interest, provided that technical closures, windows, and shutters are involved in the acoustic refurbishment.