Single-family residential buildings are most often called houses or homes . Residential buildings containing more than one dwelling unit are called a duplex , apartment building to differentiate them from 'individual' houses. A condominium is an apartment that the occupant owns rather than rents. Houses may also be built in pairs ( semi-detached ), in terraces where all but two of the houses have others either side; apartments may be built round courtyards or as rectangular blocks surrounded by a piece of ground of varying sizes. Houses which were built as a single dwelling may later be divided into apartments or bedsitters ; they may also be converted to another use . an office or a shop.