1:10 IS NOT ENOUGH
Apart from standardisation, various legally binding building regulations regulate the supply of daylight, mostly very generally via a ratio between the clear opening of the building shell and the floor area of the room to be supplied with light. For example, in the German-speaking countries it is stipulated that the total light entry area of windows, skylight domes, skylight strips, … must be at least 12.5 % of the floor area of the room. In other places, it is even specified that the rough construction dimension of the window openings must not be less than one tenth of the floor area of the room.
Such specifications are not sufficient, as they disregard the orientation and positioning of light openings, transmission or reflection properties, the geometry of the rooms as well as urban planning conditions and other parameters.