This European Standard describes the method to calculate the ventilation air flow rates for buildings to be used for applications such as energy calculations, heat and cooling load calculation, summer comfort and indoor air quality evaluation. The ventilation and air tightness requirements (as IAQ, heating and cooling, safety, fire protection…) are not part of the standard. For these different applications, the same iterative method is used but the input parameter should be selected according to the field of application. For specific applications a direct calculation is also defined in this standard. A simplified approach is also allowed at national level following prescribed rules of implementation. The method is meant to be applied to: - Mechanically ventilated building (mechanical exhaust, mechanical supply or balanced system). - Passive ducts. - Hybrid system switching between mechanical and natural modes. - Windows opening by manual operation for airing or summer comfort issues. Automatic windows (or openings) are not directly considered here. Industry process ventilation is out of the scope. Kitchens where cooking is for immediate use are part of the standards (including restaurants..) Other kitchens are not part of the standard. The standard is not directly applicable for buildings higher than 100 m and rooms where vertical air temperature difference is higher than 15K. The results provided by the standard are the building envelope flows either through leakages or purpose provided openings and the air flows due to the ventilation system, taking into account the product and system characteristics.