Field measurement of acoustical performances of buildings is difficult where construction has not been completed. The absence of doors, windows and other finishing details, generates sound transmission paths, which can modify the results of measurements. In these cases, acoustical performances of building, such as sound reduction index and impact noise, can be determined through the temporary close of all openings, or through the measurement of the vibration velocity level of the partitions examined. Both techniques allow the elimination of airborne transmission paths, while the second also permits the evaluation of the contribution of structural flanking transmission. In this paper, a technique is described for the estimation of impact noise of floors from measurements of velocity levels. Results are presented for a concrete floors and a comparison given between the traditional and new type of measurements.