Planopedia

Missing Middle Housing is defined by the planner who invented the term as a residential building that contains multiple housing units.

Dan Parolek of Opticos invented the term Missing Middle Housing in 2010 to describe the long-neglected middle of the housing spectrum, buildings ranging in size and density between a single-family detached home and a mid-rise apartment building. A common characteristic of these multiple varieties of missing middle housing is a scale comparable to a single-family house, but Missing Middle Housing always includes more than one housing unit. The varieties of Missing Middle Housing include duplexes, triplexes, and fourplexes, courtyard apartments, bungalow courts, townhouses, multiplexes, and live/work units.  

These types of residential buildings are described as 'missing' because for many decades, this kind of housing has been illegal to build in almost every corner of almost every U.S. city. Most cities in the United States (and some other parts of the world as well) have favored single-family homes over all other kinds of housing, except in the relatively small number of urban areas where apartment buildings are allowed. The preference for single-family homes and the sequestering of large multi-family residential buildings to a few small corners of large regions have been reinforced by the long-term adoption of exclusionary zoning codes, described as "exclusionary" exactly for this effect of banishing all kinds of residential development other than the prototypical American home.  

As the consequences of exclusionary zoning have become more apparent in the rising housing prices in growing urban areas and the negative economic and social outcomes of resulting segregation, new forms of density have become more politically acceptable in many parts of the country. In many cases, Missing Middle Housing is exactly the kind of new density legislated into effect, most famously with state laws that allow Accessory Dwelling Units statewide in California and laws that allow more than one residential unit on residential lots in Minneapolis and the state of Oregon. The cause has even reached Nebraska, which, as of this writing, is considering a law called the Missing Middle Housing Act, which would allow more than one unit to be built on properties previously zoned for single-family homes in almost every city in the state.

These legislative achievements have brought renewed attention to the term, and much of the news and commentary discussing these new laws uses the term Missing Middle Housing to describe the intended goal of the new laws. When used in the new media, in fact, the term Missing Middle Housing can be thought of as a shorthand for density. Some writers will use a term like "gentle density" interchangeably with Missing Middle Housing.

These few landmark achievements fall far short of universal acceptance, and Missing Middle Housing is still politically controversial, viewed by some as a threat to the single-family, exclusionary zoning status quo. In Virginia, for instance, laws to legalize Missing Middle Housing in single-family residential neighborhoods failed to achieve the necessary political support. Even in cities and states with more permissive approaches to Missing Middle Housing, zoning codes need to be updated and the real estate market has to show the necessary demand to start the process of transforming the built environment with higher-density options.

Missing Middle Housing is often described relative to its context, as a key component of neighborhoods that are more walkable and have the density to support widespread use of public transit and locally-serving retail. Advocates for Missing Middle Housing also point to the environmental benefits of smaller homes in more walkable, transit-accessible neighborhoods.