Duplex (building)

Variants

US

In dense areas like Manhattan and downtown Chicago, a duplex or duplex apartment refers to a maisonette, a single dwelling unit spread over two floors connected by an indoor staircase. Similarly, a triplex apartment refers to an apartment spread out over three floors. These properties can be quite expensive and include the most expensive property in Manhattan as of 2006 (according to Forbes magazine), a triplex atop The Pierre hotel. In this context, an apartment located on only one floor may be called a simplex.

UK

In the United Kingdom, the term duplex is sometimes used by property professionals such as architects and estate agents and refers only to a flat or apartment on two floors connected by an inner staircase though many newer apartments have open-plan designs including mezzanines. The far more commonly used term is 'maisonette' meaning two dwellings split horizontally, like flats, but each with their own separate external door, unlike flats which have a shared external door.

Australia

In Australia, a duplex is often considered a residential building containing two homes that share a common central wall. As such they are usually a mirror image of each other in layout. Also referred to as a maisonette in South Australia.

Back-to-back duplex

A Back-to-back duplex is two homes that have a shared back wall and have opposite front entries. The whole building is designed to look like one single larger home. Unlike a side-by-side duplex, the Back-to-back duplex helps provide more privacy for the homeowners.

Urban planning

In urban planning, the term duplex is used more specifically. Major Canadian cities sometimes use the term duplex to refer specifically to a building with one unit built above another. Edmonton defines 'Duplex Housing' as "a building where 1 principal Dwelling is placed over another principal Dwelling, in whole or in part, within a single building" where "each principal Dwelling has separate and individual access". Calgary defines Duplex Dwelling as "a building which contains two Dwelling Units, one located above the other, with each having a separate entrance". Toronto proposes in their new Zoning Bylaw to define 'Duplex Building' as a building that has only two dwelling units, and one dwelling unit is entirely or partially on top of the other dwelling unit. Halifax defines Duplex Dwelling as "the whole of a dwelling that is divided horizontally into two separate dwelling units, each of which has an independent entrance".

Other major cities use the term duplex, but for dwelling units. Dallas defines the term duplex as "two dwelling units located on a lot". Philadelphia defines a duplex dwelling as "a dwelling occupied as the home or residence of two (2) families, under one (1) roof, each family occupying a single unit", a definition that excludes a pair of twin (semi-detached) houses, two dwellings separated by a firewall that extends above the roofline.

Other major cities do not use the term duplex in their zoning or land-use bylaws. San Francisco and Vancouver use the term two-family dwelling. Winnipeg uses the term dwelling, two-family. The definitions of these terms do not specify the physical relationship between the two dwelling units in the building. In cities such as Buffalo, Detroit and Chicago, the term "two-flat" is used and defines as a "residential building that contains 2 dwelling units located on a single lot. The dwelling units must share a common wall or common floor/ceiling."

Where cities do not define the relationship of the dwelling units to one another, units may be built one on top of the other, or one beside the other. The latter arrangement is more specifically referred to as a semi-detached building.

Many cities in the United States, Canada, and Australia have seen an increased push to allow duplexes in more zoning districts or even in all residential zoning districts. Renewed interest in supporting duplexes in many areas is part of a larger push to support missing middle housing types and related affordability, sustainability, and urban design goals.

References

References

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2. "Definition of FOURPLEX".
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21. (2015-10-14). "Reasons to Invest in Missing Middle Housing: A Call to Action for Cities and Developers".
22. (2019-12-04). "'Gentle' density can save our neighborhoods". The Brookings Institution.