Flanking sound is transmitted indirectly via paths such as windows, external walls and internal corridors. It is defined as sound from a source room but not via a common building element. It is imperative that flanking transmission is considered at the design stage and that the construction detailing specified will eliminate or at least minimise any downgrading of the acoustic performance.

The Part E recognises that the practicalities of construction will mean that acoustic performances measured in the laboratory will be more difficult to achieve on site. To assist the designer, good practice detailing at key junctions is provided throughout the new Approved Document E. Solutions are presented showing the essential gap filling, joint sealing, fire-stopping, cavity closing and continuity of insulation to prevent sound transmission through critical junctions.