Surface condensation and mould affect about 15% of the UK housing stock. This paper reports BRE work undertaken in occupied dwellings to identify the effectiveness of a range of remedial measures in various situations. The remedies investigated include the improvements to insulation levels, andheating systems, the provision of extract fans and dehumidifiers. The studies were undertaken in both flats and 2-storey houses, all of traditional construction with brick walls and pitched roofs.