A semi-detached house (often abbreviated to semi) is a single-family duplex dwelling that shares one common wall with its neighbour. The name distinguishes this style of construction 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.[1] Between 1945 and 1964, 41% of all properties built were semis. After 1980, the proportion of semis built fell to 15%.[2]