Detailed method proposed by the standard EN 12354-2 regarding the evaluation of impact sound insulation of floors requires knowledge of physical and mechanical parameters concerning floor and lateral walls involved in flanking transmission. Most of these parameters are empirical mean values based on statistical data of similar structures. Hollow brick and beam floors are complex systems and their acoustic performances are sometimes influenced by different processes, boundary conditions and workmanships effects that can produce high spread from theoretical values. In this work a sensitivity analysis of different parameters in accordance to the simplified and detailed (frequency) methods of the EN 12354-2 is presented, based on "in situ" measurements of brick and concrete floors of Italian dwellings.