Vapour barrier
A vapour barrier is a plastic membrane laid under the slab to improve its performance against rising damp. It is also called a 'moisture barrier' because it stops the moisture from the soil migrating into the concrete slab. This must be placed under the slab for all areas where there are to be habitable rooms.
Care should be taken not to tear or puncture the vapour barrier. Any tears that occur, and joints, must be adequately taped.