Well, at least in Italy (where I was born) and France it's not allowed to have civil accommodations without openable windows. In Italy at all, in France you are

Well, at least in Italy (where I was born) and France it's not allowed to have civil accommodations without openable windows. In Italy at all, in France you are allowed for non-living areas (bathroom and kitchens essentially) as long as another form of ventilation is present. Limits I know are 1/8 of the flat surface you can march on must be openable windows, 1 complete air change per hour (you have a 50m³ room, you must change at least 50m³ of air per hour. There are some tolerance for historic buildings down to 1/12 of the flat surface, below that the accommodation can't be used to live in. While for offices there is only an natural illumination requirement, and a ventilation NOT necessarily bound to openable windows. I do not know for the rest of the EU.