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Duplex housing in North American is a dwelling which has two apartment style units that share a common wall. They have separate entrances, and living space for two households. A duplex can be single story or two-story structures with a full apartment on each floor. Additionally, they can be apartments with a side-by-side layout on one lot which shares a single wall, referred to as common wall. In comparison, building structures comprised of two attaching units on two different properties is usually referred to as aa twin home or semi-detached house, but some can be classified as a duplex.

Because of the definition of a duplex (meaning two), the term cannot extend use for three-unit or four-unit structures. Rather, these type of design layouts are referred to their own specific terms, which are a triplex, fourplex, or more commonly in the case of four units a quadplex. Additionally, the line between a duplex and apartment building is often unclear due to the term’s flexibility. However, a duplex is typically about the size of a regular house, while apartment buildings are generally bigger.

In British English areas, the term duplex simply refers to the number of floors in an apartment unit, therefore, duplex means two-story. This was traditionally called a maisonette. Furthermore, triplex means 3-story, and duplex is never used to describe a semi-detached house.


There are different variants associated with duplex’s, depending on the area.

Large Cities

In highly populated cities like Chicago or Manhattan, duplex is used to describe single dwellings which extend over two-stories which are connected with an indoor staircase. Additionally, the term duplex apartment may be used. Meanwhile, a triplex apartment is the term used for apartments that extend 3-stories. In larger cities, the cost of this type of property can be expensive. In 2006, according to Forbes Magazine, duplex apartments were the most expensive property found in Manhattan.


Property professionals, including estate agents, architects, etc. most commonly use the term duplex to describe an apartment or flat with a two-story layout, connected by a staircase. Most new apartment designs provide open-plan designing, such as mezzanines, while traditional layouts are known as maisonette.


A duplex in Australia is commonly thought to be a residential building that contains two separate residence shared by a common wall in the middle. In addition, the layout designs are typically a mirror of the other. South Australia also refers to these type of structures as maisonette.

Pair Home

The term paired home is used for describing residential structures which share a wall, with entries at opposite sides of the structure. The entire building is constructed to appear as a large single home, unlike a duplex with a front-to-front design. The homeowners are provided additional privacy by a paired home, compared to a traditional duplex style home.

“Duplex House” 2010. Retrieved 1 July 2010.