Existing timber and concrete floor specifications

If the existing floor is timber then gaps in floor boarding should be sealed by overlaying with hardboard or filled with sealant – (a) Where floor boards are to be replaced, boarding should have a minimum thickness of 12 mm, and mineral wool (minimum thickness 100 mm, minimum density 10 kg/m³) should be laid between the joists in the floor cavity. (b) If the existing floor is concrete and the mass per unit area of the concrete floor is less than 300 kg/m², or is unknown, then the mass of the floor should be increased to at least 300 kg/m². Any air gaps through a concrete floor should be sealed. A regulating screed may also be required. (c) If there is an existing lath and plaster ceiling it should be retained as long as it satisfies other requirements. (d) Where the existing ceiling is not lath and plaster it should be upgraded as necessary to provide at least two layers of plasterboard with joints staggered, total mass per unit area 20 kg/m².