Only as a data point, since 1975 there is Law here in Italy that makes some minimum requisites for living spaces, main points: 1) to be legally recognized (as

Only as a data point, since 1975 there is Law here in Italy that makes some minimum requisites for living spaces, main points: 1) to be legally recognized (as a self-standing home) the surface of an apartment cannot be less than 28 square meters 2)the minimum height of rooms intended for "long permanence of humans" (which is anything but bathrooms, corridors and closets that can be as low as 2.40 m) must be 2.70 meters 3) all rooms as above need to have a window no less than 1/8 of the surface of the room 4) there must be at least one bathroom in the house with all four pieces: basin, bidet, wc and bathtub (or shower) 5) the size in #1 is intended for a "single" person residing in it, the minimum size for two people is 38 square meters and for each person living in the house (this is not usually enforced in practice) there must be at least 14 square meters of surface (up to the first four) and 10 square meters for each more person Very often local councils impose bigger sizes for the minimum apartment (in case of new constructions or refurbishing of old houses divided in more apartments).