Only as a data point, in Italy the minimal size a house can legally be called a house is 28 sqm, intended for a single, then you add 10 sqm for each additional

Only as a data point, in Italy the minimal size a house can legally be called a house is 28 sqm, intended for a single, then you add 10 sqm for each additional adult (this is national law, since 1975). Local laws may increase these mimimum sizes, the tendency is to set the minimum to around 40-45 sqm in many places.