The new ventilation regulations in England and Wales (2006) introduced performance criteria for the control of mould. The UK Government's Building Regulations Research Programme funded University College London (UCL) to investigate the extent to which these are the most appropriate criteria for the control of mould in UK dwellings. This paper details work which includes an analysis of data from a national study of England's Home Energy Efficiency scheme (Warm Front). Surveys were undertaken of dwellings and households participating in the scheme in five urban areas. Half-hourly living room and main bedroom temperatures and relative humidity measurements were recorded for two to four weeks (in the heating season) in approximately 1600 dwellings. This data was also analysed to investigate the typical conditions that exist in UK dwellings and also any relationship that exists between these levels and the mould growth that was recorded. The paper also reports on extensive field work that was undertaken for other sets of dwellings in combination with laboratory and modelling work. The recommendations for the next revision of the regulations are described.