Although contrary to popular belief, the term "duplex" can have a number of different meanings in the housing world. Most commonly, a duplex will refer to a structure that has two separate entrances for two different owners or renters. Often times, this can be exhibited as a two-story dwelling having a complete apartment on each floor; tenants or owners sharing the internal space of the building but also having clearly private living areas of their own. However, side-by-side duplexes are not uncommon and this configuration is denoted as each household sharing a common wall (or walls). Obviously, duplexes are common in urban and suburban environments where space may be at a premium.
A duplex is often a cost-effective solution when one is not able to afford a standalone home or apartment of their own. In most instances, this type of living arrangement affords a great deal of privacy for both households and is considered preferable for young families or older couples.
Living expenses such as electricity, water and gas may be shared between both parties or these bills can be included separately; this factor primarily depending on the rental or ownership agreement signed when each household (or renter) originally entered into a contract.
In times of economic downturn, sales and rentals of duplexes are seen to generally rise, as individuals and families may find themselves on rather tight budgets. It is for this reason that most real estate firms and estate agents will offer this choice amongst standalone houses and completely separate apartments.