ISO 140-16:2006, as a complement to ISO 140-3, specifies the laboratory measurement of the improvement of the sound-reduction index of a wall or ceiling when covered by an additional acoustical lining. It also provides for individual non-standardized basic elements. ISO 140-16:2006 does not deal with the sound-reduction improvement by linings on flexible lightweight structures, such as timber-frame floors or double-leaf gypsum board walls.