As part of large scale project called ‘the BIG Energy Upgrade’, to improve deprived community housing in Yorkshire and the Humber region in the UK and to examine the effectiveness of the retrofit measures, the University of Sheffield - Building Environments Analysis Unit (BEAU) has carried out an intensive monitoring programme pre and post refurbishment. Air quality, air temperatures and relative humidity levels within an indoor environment of multiple houses have been monitored as part of the ongoing project, and in this particular study, two case study dwellings have been evaluated considering the standard guidelines before and after refurbishment. Airtightness tests have been completed after retrofitting dwellings to check the air leakages through the buildings’ fabric and thermal imaging surveys have been undertaken for detection of many problems. Although the measurements pre refurbishment on indoor air quality in living spaces had showed that the levels are fluctuating around the recommended value, the findings have indicated that the warmer space has lack of air ventilation rates and therefore the CO2 levels are higher in the retrofitted dwellings that reflects the dilemma of achieving proper ventilation and indoor thermal comfort at the same time, which has been further discussed in the paper.