European Union: more single households, fewer familiers. What geography? What are the explanatory factors?

Households, i.e. all the people living under the same roof, are the basic geographical unit of socialization. Reduced fertility, which reduces family size, and aging populations, which increase the proportion of (small) elderly households, have led to a decline in average household size in the EU27. This demographic dynamic common to all EU27 countries has not, however, resulted in a homogenization of household and family characteristics between member countries. Differences, sometimes significant, remain, as other factors play a decisive role. These contribute to defining a highly diversified European Union, within which a geographical typology is nonetheless possible. What is this typology? What factors explain it?