A flooring system comprises a preformed composite panel having a first sheet (2), a second sheet (3) and a core of insulating material between the first and second sheets (2, 3). In one case the sheet (2) is a generally flat top sheet and the sheet (3) is a profiled bottom sheet. A floor such as a wood effect floor (5) is laid over the flat top sheet (2). An acoustic barrier layer 6 is located between the floor (5) and the sheet (2). The profiling of the sheet (3) defines channels (7) for location of service ducts/conduits (11). A planar facing (8) is applied over the profiled sheet, bridging the channels (7).