What is “missing middle” housing?

By BHN Editor Kathleen McCormick

Missing middle housing is in the news as state and local governments debate the new land use legislation proposed by Governor Jared Polis and the Colorado General Assembly. The senate bill SB23-213 (see accompanying article), now under consideration, calls for allowing “middle” housing, including duplexes, triplexes, townhouses, and ADUs, in single-family neighborhoods to address the state’s housing crisis and to provide more compact, sustainable, and affordable housing options linked to transportation and services. 

Missing Middle Housing concept created by Daniel Parolek/Image © Opticos Design, Inc./For more info visit www.missingmiddlehousing.com

In Boulder and elsewhere, demographic shifts, inadequate housing production, and the rising costs of land and construction have resulted in the need for new and more affordable housing choices. Baby boomers and millennials favor walkable and bikeable places linked to services and are willing to live carless (or car-light) in smaller homes that offer greater convenience, affordability, and community with less environmental impact. Working families at low and middle-income levels need more diverse and affordable housing types to buy or rent. The mismatch between Colorado’s current market and lack of affordable housing options derives from land use restrictions, which devote the residential land in many cities and towns primarily to single-family zoning.

As state and municipal officials and planners begin to look for ways to introduce more housing, the missing middle concept is getting a lot of play. But what is it exactly? Most older cities have lots of examples of these traditional housing types, but in post-WWII single-family neighborhoods, what would missing middle housing look like?

At a March presentation by the Urban Design program at the University of Colorado Denver’s College of Architecture and Planning, architect, urban planner, and missing middle guru Dan Parolek shared some ideas from his 2021 book, Missing Middle Housing: Thinking Big and Building Small to Respond to the Housing Crisis. Parolek is also founder of the firm Opticos Design, which has consulted with cities , counties, and regional planning agencies across the U.S. about planning and zoning for missing middle housing types, and has worked with developers to design model Missing Middle projects. Parolek created the Missing Middle Housing concept and launched missingmiddlehousing.com in 2016. 

“Missing middle housing is often mischaracterized as middle-income housing, but it is first and foremost about house-scale buildings with multiple units in walkable neighborhoods,” said Parolek. “It’s about form, scale, and typology.” It represents the middle range of housing between single-family and large apartment or condo buildings, and encompasses a range of multi-unit or clustered housing types that are compatible in scale with single-family homes. These types are in demand and can be built for all income levels, with affordability achieved by design through smaller per-unit size and lower costs for land and construction materials and finishes. With the right zoning and thoughtful design, they can be used to deliver attainable housing, but they are also in demand from higher end households as well.

Missing middle housing types often generate densities between 35 and 70 dwelling units per acre (du/acre) in house-scaled buildings, compared to low-density single-family zoning that might have between one and 10 du/acre. However, to advocate for missing middle housing, Parolek said, “it’s important to shift the discussion away from conventional development concepts such as density, floor area ratio (FAR), and lot coverage, and instead focus on desired housing forms, scale, and types” compatible with single-family neighborhoods.

Core Housing Types

Duplex: Two typically 1,000-square-foot units are located next to each other with one shared wall, either side by side or stacked. The stacked version, known in the Northeast as the two-family house, typically can fit on a lot as narrow as 30 feet. A one-story version historically was built for attainability and still may be needed for singles and older or disabled folks; two larger two-story units are more typical today, but can still offer more attainable housing than single-family if the homeowner owns both and rents one.

Triplex: Boston and other cities know these as “triple deckers,” or three stacked 1,000-square-foot apartments. Triplexes also can be designed for a lot as narrow as 30 feet in width.

Fourplex: This small-to-medium structure consists of two units on the ground floor and two units stacked directly above them, with a typical unit size of between 700 and 1,000 square feet. It is popular with renters and buyers because it “feels and lives much like a single-family home,” notes Parolek. He calls the fourplex the “holy grail” of missing middle housing. It is an attractive project for local contractors and smaller-scale developers, he says, and enabling and building more of them is critical for cities of all sizes. 

Mansion Building: Missing middle buildings can be expanded with larger envelopes, such as a 12-apartment “mansion” building that presents like an 8,000 to 10,000 square-foot estate home. 

Form Characteristics

As a foundation for planning, design, and development strategies, the core missing middle housing types share the following form characteristics:

  • Height:  two to two and a half stories maximum
  • Footprint: 45 to 60 feet width along the street and 45 to 60 feet deep
  • Unit number: Typically 12 or fewer per building; maximum of 19
  • Open space: Shared open space exists in the rear or side yards or courtyard. Additional open space is not needed and should not be required.
  • Off-street parking: Ideally none, preferred .5, and maximum of one parking space per unit, typically provided in a separate garage behind the housing units and not embedded within the structure. Counting on street parking toward parking requirements is also recommended. 
  • Construction: Typically wood-framed, missing middle buildings are less expensive per unit to build than larger multifamily buildings.

Townhouse: The most popular missing middle housing type in recent years is the townhouse, with two or more multi-story units that share side walls, often with a front court or rear yard. Units typically are about 1,750 square feet.

Live-Work Flexhouse: In two to three stories, flexhouses provide ground-floor space for an art studio or small business with living space above. This transition type often is often woven successfully into mixed-use, medium-density, or multifamily residential zones.

Cottage Court: Often found in pre-1940s neighborhoods, the cottage court is a series of small-footprint, typically one to one and half-story detached homes, located around a shared courtyard. A rear building, parallel to the street, might feature two-story attached or stacked units.

Pocket Neighborhood: On larger or multiple lots, these can be found in cohousing and other communities, and typically feature attached, detached, and sometimes stacked homes, oriented around a shared green space and amenities such as a community house with kitchen and workshop.

In addition to providing layouts, specifications, and images of missing middle housing, Parolek’s book discusses zoning policy and regulatory changes. It also provides case studies, from converting a single-family Portland home into a fourplex, to planning a missing middle neighborhood in Nebraska. A more detailed summary and graphic examples of these types can be found on missingmiddlehousing.com. AARP recently created a Missing Middle Housing document with Opticos Design that can be downloaded for free here

Closer to home, Boulder’s Holiday and downtown neighborhoods offer excellent examples of a variety of middle housing types. But even though such traditional housing types might be allowed today in certain zones, other regulations, like those related to lot size, density limits, setbacks, and parking prevent construction. If state legislators pass a version of SB23-213, zoning revisions could remove such barriers and open up much greater diversity and affordability through middle housing types in Boulder and other cities and towns throughout Colorado.

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