Key Difference: A townhouse is a type of medium-density housing in the cities that may be terraced or semi-detached. A modern townhouse, also known as a rowhouse, is a house in a row of houses that has a small footprint, but has multiple floors. On the other hand, a duplex is a house that is characterized by apartments that has two separate entrances for two different families. A duplex may or may not have a terrace.

Townhouses and Duplexes are two different types of dwellings and each is constructed differently. While townhouses are similar to row houses, duplexes are buildings that have two housing units close to each other. Let’s look at each term separately.

A townhouse is a type of medium-density housing in the cities that may be terraced or semi-detached. A modern townhouse, also known as a rowhouse, is a house in a row of houses that has a small footprint, but has multiple floors. All the houses share a common wall in rowhouses. The term ‘townhouse’ refers to a city residence of a wealthy or noble family, who usually reside in their country homes most of the year. These homes in the city used to be an alternate residence that was used during social seasons.

In the United Kingdom, town houses were usually terraced and a few of them were large and detached from each other. In Asia, Australia and South Africa, townhouses are most commonly a part of huge complexes. The houses in the complexes share common land and facilities such as swimming pools, gyms, parks and playground equipment, but maintain their own house and the surrounding land. The common place that is shared can be maintained by the Home Owner’s Association, a committee which is made up of all the house owners. A townhouse is sold in an individual capacity.

On the other hand, a duplex is a house that is characterized by apartments that has two separate entrances for two different families. A duplex may or may not have a terrace. In layman’s terms, it is a two floor house, where each floor has a separate entrance. The two floors share a common structure and they may be side by side, in which case they share a common wall. In some countries, a duplex is described as a house or maisonette or a single two-floored dwelling whose floors are connected by an indoor staircase.

The definition of the term duplex varies according to different countries. In some places a duplex can refer to a dwelling having apartments with separate entrances for two families, which can include two-story houses having a complete apartment on each floor and also side-by-side apartments on a single lot that share a common wall. Another definition refers to a building made up of two attached units on two distinct properties, sharing a wall that may be semi-detached or twin homes. The term "duplex" can also be extended to three-unit and four-unit buildings. In areas such as Manhattan or Chicago, a duplex apartment refers to a maisonette or a single dwelling unit that is spread over two floors connected by an indoor staircase. These places are pretty expensive to purchase.

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