Semi-detached housing (usually abbreviated to semi, as in "three-bedroom semi") consists of pairs of houses built side by side as units sharing a party wall and usually in such a way that each house's layout is a mirror image of its twin.

This type of housing can be thought of as being a half-way state between terraced or row housing and individual (detached) houses. Terraced housing is constituted by continuous row houses with open spaces at the front and back, semi-detached houses have front, rear and any one side open spaces and individual detached houses have open spaces on all sides.

In the British housing boom of the 1920s and 1930s semi-detached houses sprang up in suburbs throughout the country, and were popular with middle class home owners who preferred them to terrace houses. The design of many of these house, highly characteristic of the era, was heavily influenced by the Art Deco movement. Other typical suburban developments were designed in mock Tudor, and chalet styles.

In the immediate post-war years many council houses also followed the 'semi' format, giving many people a first experience of private garden space.

During the house price boom in the years to 2004 many property developers found they could create value by demolishing semi-detached houses and building two detached houses on the same site, often with a very narrow gap between the new units.

See also

• Duplex
• List of house types
• Townhouse
• Terrace