As a result of new inquiries in 20 countries the ventilation requirements will be presented for different rooms in dwellings, offices and schools. These rooms are differentiated between wet rooms such as toilets, bathroom and kitchen and typical rooms for these buildings for instance classrooms and office rooms. The results show big differences between countries. Climate and building style can have an effect on ventilation requirements. Some countries have to only requirements for specific rooms but also for whole house and whole building ventilation. The reasons behind these differences will be discussed and analysed in the final presentation of this session. The results are also compared with recent CEN and ISO standards. Ventilation requirements do not only consist of a required flow rates but also the way to assess this requirement in design and real practice. The assessment method itself may lead quite different results in practical design. For example in case of natural supply the pressure difference in the Netherlands (1 Pa), Belgium (2 Pa) and France (20 Pa) at which one should fulfil the requirements leads to quite different approaches of ventilation systems.