In new constructions, the subfloor must have reached the required level of dryness before the floor covering installation can proceed. The moisture content of the subfloor must be tested with a hygrometer. The relative humidity (RH) should be below 75% RH. If the reading is above this level, the floor will be considered unsuitable for a resilient floor covering so other appropriate measures will need to be considered e.g. the application of a surface damp proof membrane (DPM).
Subfloor moisture levels in concrete - when am I ok to install my Forbo Flooring
In older constructions, the floor slab must have an effective structural damp proof membrane. If it does not or if there is any doubt a surface damp proof membrane should be applied.