For residential buildings, these norms are 48-96 kWh/m2/year or 38-44 kWh/m /year if heat recovery ventilation is used. The norm in both cases depends on the number of floors. Energy efficient practice over the period 2007-2014 has resulted in 9 per cent of the national housing stock, or 1.6 million m , having been built to the thermal energy standard of less than 90 kWh/nr.