Reports on an investigation concerning ventilation and energy conservation in dwellings, which was financed by the EEC and the Dutch Ministry for Housing and Public Works. Concludes that:< 1. In single family houses air flow through cracks and joints causes more ventilation then is required.< 2. Flats with more airtight construction provide better control of ventilation.< 3. The amount of wind protection plays a part as important as airtightness.< 4. Predictions can be made using a calculation model, providing that accurate input data such as pressure distribution and position and size of openings in the outer shell of the dwelling are known.<5. As a result of excessive ventilation of dwellings, at least 14% of the total energy consumption of a dwelling is unnecessary.< 6. To acheive reduction of energy wasted through open windows, education of the occupants is required.