Duplex (building)

{{Short description|Type of residential building}} {{Other uses|Duplex (disambiguation)}} {{Use dmy dates|date=May 2023}} thumb|An over-and-under two story apartment duplex in Southeastern Pennsylvania [[File:Sausalito-modern-duplex.jpg|thumb|A large, modern side-by-side duplex in downtown Sausalito, California]]

A '''duplex''' house plan has two living units attached to each other, either next to each other as townhouses and condominiums or one above the other like apartments. By contrast, a building comprising two attached units on two distinct properties is typically considered ''semi-detached'' or ''twin homes'' but is also called a ''duplex'' in parts of the Northeastern United States, Western Canada, and Saudi Arabia.

The term "duplex" is not extended to three-unit and four-unit buildings, as they would be referred to with specific terms such as '''three-family''' (or '''triplex'''<ref>{{cite web|url=https://www.merriam-webster.com/dictionary/triplex|title=Definition of Triplex}}</ref>) and '''fourplex''' (or '''quadplex'''/'''quadruplex''') or a more general '''multiplex'''.<ref>{{cite web|url=http://www.m-w.com/dictionary/fourplex|title=Definition of FOURPLEX}}</ref> Because of the flexibility of the term, the line between an apartment building and a duplex is somewhat blurred, with apartment buildings tending to be bigger, while duplexes are usually the size of a single-family house.

Certain jurisdictions may describe these as '''paired homes'''.<ref>{{cite web |title=Middle Housing Design Guidelines - Addendum to Design Guidelines for New Construction |url=https://www.orcity.org/DocumentCenter/View/3929/Design-Guidelines-New-Construction---Middle-Housing-Addendum |publisher=Oregon City |access-date=15 February 2026 |date=17 May 2023}}</ref>

==Variants== ===United States=== [[File:US Navy 061106-N-1023B-014 U.S. Navy Petty Officer Steve Wagner and his family prepare to move into a newly constructed home during a ribbon cutting ceremony at the Village at Whitehurst.jpg|thumb|A side by side duplex also known as a semi-detached house]]

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.<ref>{{cite web|url=https://www.rentkidz.com/chicago-duplex-apartments/|archive-url=https://web.archive.org/web/20200730051156/https://www.rentkidz.com/chicago-duplex-apartments/ |url-status=usurped |archive-date=30 July 2020|title=Chicago Duplex Apartments}}</ref> 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.<ref>[https://www.forbes.com/2006/06/23/cx_0626homeland.html "Most Expensive Homes in the U.S. 2006"]. ''Forbes'' (23 June 2006). Retrieved on 2011-06-07.</ref> In this context, an apartment located on only one floor may be called a simplex.

===United Kingdom=== 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=== thumb|Back-to-back duplexes Back-to-back duplexes are variants where the homes have a shared back wall and have opposite front entries.<ref>{{Cite web |title=Duplex House Plans, Back To Back House Plans, Narrow House Plans, |url=https://www.houseplans.pro/plans/plan/d-589 |access-date=2025-10-27 |website=www.houseplans.pro}}</ref>

==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".<ref>{{cite web |url=https://zoningbylaw.edmonton.ca/duplex-housing |title=Duplex Housing - City of Edmonton Zoning Bylaw |access-date=27 May 2025 |archive-url=https://web.archive.org/web/20250418233136/https://zoningbylaw.edmonton.ca/duplex-housing |archive-date=18 April 2025 |url-status=live }}</ref> Calgary defines Duplex Dwelling as "a building which contains two Dwelling Units, one located above the other, with each having a separate entrance".<ref>{{cite web|url=http://www.calgary.ca/docgallery/bu/dba/land_use_bylaw_review/bylaw_1p2007.pdf|title=Calgary Land Use Bylaw|access-date=23 February 2018|archive-url=https://web.archive.org/web/20110807113054/http://www.calgary.ca/docgallery/bu/dba/land_use_bylaw_review/bylaw_1p2007.pdf|archive-date=7 August 2011|url-status=dead}}</ref> 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.<ref>{{cite web|url=http://wx.toronto.ca/zoning.nsf/8459fb1d5a5fdfa785256f2300664bcd/670673999d4548f885256f410055fe80?OpenDocument|title=Proposed Toronto Zoning Bylaw|access-date=23 February 2018|archive-url=https://web.archive.org/web/20110716201311/http://wx.toronto.ca/zoning.nsf/8459fb1d5a5fdfa785256f2300664bcd/670673999d4548f885256f410055fe80?OpenDocument|archive-date=16 July 2011|url-status=dead}}</ref> 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".<ref>{{cite web|url=http://www.halifax.ca/planning/documents/HalifaxMainland_LUB.pdf|title=Halifax Mainland Land Use Bylaw|access-date=23 February 2018|archive-url=https://web.archive.org/web/20160406110115/http://www.halifax.ca/planning/documents/HalifaxMainland_LUB.pdf|archive-date=6 April 2016|url-status=dead}}</ref>

Other major cities use the term duplex, but for dwelling units. Dallas defines the term duplex as "two dwelling units located on a lot".<ref>{{cite web|url=http://dallascityhall.com/departments/sustainabledevelopment/planning/Pages/zoning.aspx |title=Dallas Zoning Code|access-date=23 February 2018}}</ref> 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.<ref>{{cite web|url=http://www.amlegal.com/nxt/gateway.dll/Pennsylvania/philadelphia_pa/title14zoningandplanning/chapter14-100generalprovisions?fn=altmain-nf.htm$f=templates$3.0|title=File Failed|access-date=23 September 2008|archive-url=https://web.archive.org/web/20090327023324/http://www.amlegal.com/nxt/gateway.dll/Pennsylvania/philadelphia_pa/title14zoningandplanning/chapter14-100generalprovisions?fn=altmain-nf.htm$f=templates$3.0|archive-date=27 March 2009|url-status=dead}}</ref>

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.<ref>{{cite web|url=http://www.city.vancouver.bc.ca/COMMSVCS/BYLAWS/zoning/sec02.pdf|title=Vancouver Zoning and Development Bylaw|access-date=23 February 2018|archive-url=https://web.archive.org/web/20060613002953/http://city.vancouver.bc.ca/commsvcs/bylaws/zoning/sec02.pdf|archive-date=13 June 2006|url-status=dead}}</ref><ref>{{cite web|url=http://www.municode.com/Resources/gateway.asp?pid=14139&sid=5|title=San Francisco Planning Code|access-date=23 February 2018|archive-url=https://web.archive.org/web/20081021150918/http://www.municode.com/Resources/gateway.asp?pid=14139&sid=5|archive-date=21 October 2008|url-status=dead}}</ref> Winnipeg uses the term dwelling, two-family.<ref>[http://www.winnipeg.ca/CLKDMIS/Documents/DocExt/BL/2006/2006.200.cons.pdf Winnipeg Zoning Bylaw]</ref> 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."<ref>{{cite web|url=http://www.amlegal.com/nxt/gateway.dll/Illinois/chicagozoning/chicagozoningordinanceandlanduseordinanc?f=templates$fn=default.htm$3.0$vid=amlegal:chicagozoning_il|title=American Legal Publishing – Online Library}}</ref>

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.<ref>{{Cite news|date=2021-03-01|title=The Upzoning Wave Finally Catches Up to California|language=en|publisher=Bloomberg News|url=https://www.bloomberg.com/news/articles/2021-03-01/california-turns-a-corner-on-single-family-zoning|access-date=2021-03-13}}</ref><ref>{{Cite web|last=Kahlenberg|first=Richard D.|date=2019-10-24|title=Minneapolis Saw That NIMBYism Has Victims|url=https://www.theatlantic.com/ideas/archive/2019/10/how-minneapolis-defeated-nimbyism/600601/|access-date=2021-03-13|website=The Atlantic|language=en}}</ref><ref>{{Cite web|date=2020-08-11|title=Portland just passed the best low-density zoning reform in US history|url=https://www.sightline.org/2020/08/11/on-wednesday-portland-will-pass-the-best-low-density-zoning-reform-in-us-history/|access-date=2021-03-13|website=Sightline Institute|language=en-US}}</ref><ref>{{Cite web|last=Edmonton|first=City of|date=2021-03-13|title=Missing Middle Zoning Review|url=https://www.edmonton.ca/city_government/urban_planning_and_design/medium-scale-housing-review.aspx|access-date=2021-03-13|website=edmonton.ca}}</ref><ref>{{Cite web|title=Low Rise Housing Diversity|url=http://www.planning.nsw.gov.au/Policy-and-Legislation/Housing/Low-Rise-Housing-Diversity-Code|access-date=2021-03-13|website=planning.nsw.gov.au|language=en}}</ref> 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.<ref>{{Cite web|date=2015-10-14|title=Reasons to Invest in Missing Middle Housing: A Call to Action for Cities and Developers|url=https://opticosdesign.com/blog/reasons-to-invest-in-missing-middle-housing-a-call-to-action-for-cities-and-developers/|access-date=2021-03-13|website=Opticos Design|language=en-US}}</ref><ref>{{Cite web |last1=Baca |first1=Alex |author2=Patrick McAnaney |author3=Jenny Schuetz|date=2019-12-04|title='Gentle' density can save our neighborhoods|url=https://www.brookings.edu/research/gentle-density-can-save-our-neighborhoods/|access-date=2021-03-13 |publisher=The Brookings Institution |language=en-US}}</ref>

==See also== {{Portal|Housing}} {{Div col}} <!-- This section needs explanations of how these other types contrast with "duplex". --> * Apartment * Condominium * List of house types * Medium-density housing * Polish flat * Semi-detached * Split-level home * Triple-decker triplex * Tyneside flat {{Div col end}}

==References== {{reflist}}

== External links == * {{Commons category-inline|Duplexes (buildings)}} * {{Wikiquote-inline}}

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{{DEFAULTSORT:Duplex (Building)}} Category:House types *