Detached houses are very popular among the people for the reason that the houses offer privacy and are seen as more prestigious than other types of property.
These are selected by those people who need to stay in big places with their family and also crave privacy. These houses are built on either large or small plots of land. Whatever size plot of land semi detached houses are built on, there is almost always enough space for the inhabitants to start their own garden. A private garden in an urban or semi urban area is a big factor in determining the house's value.
Gardening is a very popular hobby in The UK, and as such the demand for semi detached houses which have their own garden is traditionally very high. The relaxing effects of having a little greenery and space in your own property are a big draw and property buyers are usually willing to pay a great deal more for a semi detached house if it has its own garden.