A duplex is a structure that consists of two separate family units. Some localities require a building permit for a new single-family dwelling/duplex. Definitions and requirements vary by locality, so local laws should be consulted for applicability in your area. The following is an example of a city definition of a duplex:
"Duplex Dwelling is a dwelling occupied other than as a single-family or multi-family dwelling and which is occupied or intended to be occupied more or less permanently for residential purposes by two (2) families, which dwelling is not licensed as a rooming house under the Code of Ordinances for the City of Escanaba."
