Duplex (building)

A duplex house plan has two living units attached to each other, either next to each other as townhouses, condominiums or above each other like apartments. The term "duplex" is not extended to three-unit and four-unit buildings, as they would be referred to with specific terms such as three-family (or triplex) and fourplex (or quadplex/quadruplex) or a more general multiplex. Because of the flexibility of the term, the line between an apartment building and a duplex is somewhat blurred, with apartment buildings tending to be bigger, while duplexes are usually the size of a single-family house.