The residential sector accounts for 25% of Ireland's total energy consumption, of which 60% is used for space heating. As thermal insulation standards increase, building air tightness is playing an increasing role in both building energy performance and indoor environmental quality. This paper reports on the results of air tightness testing carried out on a small number of dwellings. The paper highlights the paucity of dwelling airtightness data for Ireland. The results are compared to past studies and compliance with the existing standards. While the number of houses tested is small they are broadly representative of urban dwellings in Ireland. The study indicates a misconception that newer buildings are more airtight than older buildings. The paper concludes that good design, attention to detail and rigorous controls throughout construction is vital to delivering air-tight dwellings.