In recent years there has been much emphasis on improving the energy performance of Irish buildings. Much of this impetus stems from our requirements to implement provisions in the Energy Performance Building Directive (EPBD, 2002/91/EC, 2010/31/EU), and international targets to reduce CO2 emissions by 2020. In Ireland, residential buildings account for 27% of Irelandís CO2 emissions after transport. As a large proportion of the Irish building stock has already been built home owners are encouraged to retrofit existing buildings to improve the energy rating. The impact of retrofitting residential buildings to improve energy rating on indoor air quality and comfort has largely been unexplored. This study proposes to conduct an assessment of indoor air quality and occupant comfort in 60 retrofitted energy efficient homes. Thermal comfort and occupant behaviour in retrofitted energy efficient home will also be assessed using an occupant survey. This is the first time that a full study of indoor air quality in retrofitted energy efficient homes will be completed in Ireland, and represents one of very few such studies conducted internationally.