Concrete ground floors first became widespread in the 1950s. Since the mid-1990s they have been constructed to include insulation (1). 70mm of rigid foam insulation can be installed above uninsulated concrete floors.
Although most newer buildings have concrete floors, timber floors are still widespread. They are especially common in older buildings, which are most likely to have a ground floor made of suspended timber. Signs that a building has a suspended timber floor include air or ventilation bricks on the outside walls below floor level. Timber floors can be insulated with approximately 150mm of mineral wool supported by netting between the joists under the floorboards. (2)
(1) University of the West of England, Evolution of Building Elements, Ground Floors. Available from: https://fet.uwe.ac.uk/conweb/house_ages/elements/section3.htm [Accessed 26th January 2021].
(2) Energy Saving Trust, Reducing Home Heat Loss, Floor Insulation. Available from: https://energysavingtrust.org.uk/advice/floor-insulation/ [Accessed 26th January 2021].