This research work deals with the effects of junction construction details on airborne sound insulation in buildings and the analysis of flanking transmissions across double ceramic brick walls with elastic interlayers.The sound transmission between two adjacent rooms comprises two paths: the direct path, caused by the incident sound on a separating wall, and the indirect path, through flanking elements connected to the separating wall, such as floors, internal walls, ceilings, etc. Flanking elements vibrate when excited in the sound field, thus transferring sound via structure borne to the receiving room. Dominant flanking transmissions can decrease the field sound insulation performance of the building.The vibration reduction index, K ij. expresses the acoustic attenuation of construction joints. This is an input parameter in the calculation models designed to estimate the airborne sound insulation between adjoining rooms in buildings. These models are used to comply with the acoustic requirements set by "Basic Document DB HR Protection against noise" included in the "Spanish Building Code". The characterization of K ij. must be addressed experimentally by means of measurements. The available empirical K ij. formulae were developed in different European laboratories, but they have not been validated with standard tests performed on common Spanish walls, such as those studied in this work.