Air tightness (or permeability) is a property of a building envelope that describes how air moves though it when subjected to a pressure difference (wind, stack effect, etc.), this impacts on building performance including energy usage, thermal comfort and air quality. The NSW Land and Housing Corporation (LAHC) implemented a pilot program of simple leak (or draught) sealing measures to improve air permeability and building performance on some of its domestic building stock. The effectiveness of this program was evaluated via blower door testing to international standards including measuring overall envelope permeability, and qualitative and quantitative investigation of the leakage paths through the structure. Testing was undertaken before and after the leak sealing interventions to determine the relative impact, the extent of the works implemented was documented, and potential for further improvements investigated.