Two series of pressurisation and ventilation measurements have been made in a low-energy house. One of the objectives of the work was to assess the extent to which the ventilation pattern of the house could be improved by modifying its leakage distribution. The first series of measurements was interpreted to understand the ventilation pattern and to make recommendations for the modifications. The second series was used to find out the effects of the modifications. Throughout this paper the term ventilation rate is used to denote the volume flow rate of air entering a room (or the whole house) directly from outside, divided by the volume of the room i.e. the ventilation rate of the room is the fresh air change rate. The term stack effect denotes the temperature difference between the inside and the outside of the house.