Flanking Transmission

Flanking transmission is the transmission of sound between rooms via paths other than directly through the separating element, including structure-borne paths through connected floors, walls, and junctions. In practice, flanking often limits the achievable sound insulation between rooms, regardless of the separating partition’s performance. For example, a wall rated Rw 60 in the laboratory may only achieve DnT,w 50 in the field due to flanking through the floor slab and side walls. EN 12354-1 provides a calculation framework for predicting flanking contributions using junction vibration reduction indices (Kij). Common flanking paths include continuous floor slabs, common ceiling voids, back-to-back electrical outlets, HVAC ductwork, and structural connections at wall-floor junctions. Addressing flanking requires structural isolation (resilient connections, floating floors, independent leaf constructions), sealing penetrations, and careful junction detailing. Flanking assessment is essential in building acoustic design to ensure that the specified insulation target is achievable in the completed building.