A semi-detached house (often abbreviated to semi) is a single family duplex dwelling house that shares one common wall with the next house. The name distinguishes this style of house from detached houses, with no shared walls, and terraced houses, with a shared wall on both sides. Often, semi-detached houses are built in pairs in which each house's layout is a mirror image of the other's.
Semi-detached houses are the most common property type in the United Kingdom (UK). They accounted for 32% of UK housing transactions and 32% of the English housing stock in 2008. Between 1945 and 1964, 41% of all properties built were semis. After 1980, the proportion of semis built fell to 15%.
History of the semi-detached house in the United Kingdom
Housing the rural working classes
Housing for the farm labourer in 1815 typically had one downstairs room with an extension for a scullery and pantry, and two bedrooms upstairs. The house would be of brick, stone if it occurred locally, or cob on a wooden frame. These houses were unsanitary, but the biggest problem was that there were simply too few of them. Population was increasing rapidly (see table), and after the Enclosure Acts labourers could not find spare land to build their own homes. Homebuilding was thus the responsibility of a landowner or speculative builder.
In the late 18th century, estate villages followed local architectural styles. This later changed as landowners adopted model designs from pattern books. By the early 19th century, landowners were typically using a "picturesque" style, and building double cottages as a way to reduce cost. In 1834, Edinburgh architect George Smith wrote "this species of cottage can be built cheaper than two single ones, and, in general, these double cottages are found to be warmer and fully as comfortable as single ones".
Housing the urban working classes
At the same time as the huge increase in the population of the rural counties there was an even greater shift in population from the impoverished land to the large towns and to cities. Society was restructuring, with the labouring classes dividing into artisans and labourers. In the cities, labourers were housed in overcrowded tenement blocks, rookeries and lodging houses, and philanthropic societies aimed to improve conditions. The rural Labourers' Friend Society expanded in 1844 and was reconstituted as the Society for Improving the Condition of the Labouring Classes. In their 1850 publication The Dwellings of the Labouring Classes, written by Henry Roberts, the society laid out plans for model 'semi-detached' cottages for workers in towns and the city. However, the first properties they built were tenements and lodging houses.
In 1866 the Metropolitan Association for Improving the Dwellings of the Industrious Classes built Alexander Cottages at Beckenham in Kent, on land provided by the Duke of Westminster. The development initially comprised 16 pairs of semis. By 1868, they had built 164 semis.
In Birmingham, Wolverhampton and the Potteries there was a tradition dating from the 1790s of artisans saving through mutual funds and Friendly Societies. In the 1840s, the permanent building society model was adopted. The Woolwich Equitable was founded in 1847, the Leeds Permanent in 1848 and Bradford Equitable in 1851. Artisans could invest and then borrow a sum for a mortgage on their own property.
Model villages
In the wool towns of Yorkshire three families built villages for their workers. In each, there was a hierarchy of houses: long terraces for the workers, larger houses in shorter terraces for the overlookers, semi-detached houses for the junior managers, and detached houses for the elite. The first such village was built by Colonel Edward Ackroyd, at Copley, West Yorkshire, between 1849 and 1853, the second by Sir Titus Salt at Saltaire (1851–1861), and the third was the West Hill Park Estate in Halifax built by John Crossley. Model villages in Lancashire followed, with developments like Houldsworth Village. Semi-detached housing in colliery villages was rare; status here was determined by the length of the terrace.
The development of Port Sunlight and Bournville was important. The Port Sunlight model village was begun in 1887. William Lever used architects William Owen and his son Segar Owen and stated in 1888 that:
It is my and my brother's hope, some day, to build houses in which our work-people will be able to live and be comfortable – semi-detached houses with gardens back and front, in which they will be able to know more about the science of life than they can in a back-to-back slum.