The document describes the essential acoustical effects of raised access floors and hollow floors, which are significant for layout and installation. Longitudinal sound insulation, impact sound insulation, airborne sound insulation of floor ceilings and horizontal impact sound transmission are considered. Furthermore, the effect on room acoustics and the fundamental of walking noise are covered. Hints are given on how to determine the acoustical performance of raised access floors and hollow floors taking into account the other flanking elements, as well as on how to proceed to obtain a required acoustical performance.