Semi-detached

Semi-detached house (usually abbreviated to semi, as in "three-bedroom semi" and known as a duplex in the USA and Europe and townhouse in Australia), 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 style of housing, although built throughout the world, is commonly seen as particularly symbolic of the suburbanisation of the United Kingdom.

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, taking influence from mock Tudor style, chalet styles and even ship design.

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

In Australia, townhouses and are generally found in complexes. Large complexes usually have high security, resort facilities such as swimming pools, gyms, parks and playground equipment.

During the house price boom in the years to 200 many UK 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.