A duplex is a house which has two separate entry points for the separate people living in the same house. This term can also be given to three unit and four unit buildings. In these cases they are then called triplex and fourplex. The difference between apartments and duplexes is only in the area on which they are made. Duplex houses have a complete apartment for each separate family on each floor of the house. This can also be separated by side by side apartments on a single floor. Sometimes semi-detached or even twin homes are given the name of duplex.
These kinds of houses are usually expensive. Duplex apartments are spread over two stories and connected with an inside door. This can also be a three storey building which has inside doors to connect the different parts of the building. These kinds of buildings are very expensive and usually selected by affluent people who can afford them. The common people in most countries however opt for duplex houses. These houses are simple and they can be used easily by people for their whole family. Duplex houses are quite common in many parts of the United Kingdom.