Mixed-use live/work housing types in Kentlands, Maryland © Opticos Design, Inc.

How to Regulate

Allowing and encouraging diverse housing types within a neighborhood

Conventional Zoning Doesn’t Work

Conventional (Euclidean) zoning practice assigns blocks and/or large areas of a city based on land use or allowed activities. Along with use, the zones are often defined and controlled by placing numeric values to their build-out, including floor area ratio (FAR) and a range of allowed density, dividing neighborhoods into single-family residential, multifamily residential, commercial, office, etc.

This Alameda, CA neighborhood has several Missing Middle housing types on each block.
This Alameda, CA neighborhood has several Missing Middle housing types on each block.

Missing Middle Housing cannot be effectively regulated by conventional, land-use and density-based zoning because these building types often have medium to high densities, excluding them from the singly-family use zone, but their small footprints with lower heights don’t meet the requirements of multifamily use zones.

  1. There is usually a gap in the range of housing types that a city or county’s zoning districts allow, and more importantly encourage, in particular when the zones shift from upper (smaller lot) single-family zones that only allow single-family detached uses/homes and the lower end of medium density/multifamily zones that usually allow much bigger buildings (taller and wider) and also typically encourage lot aggregation and suburban garden apartment-type buildings.
  2. Density-based zoning districts cannot allow the blended densities that are typically inherent in neighborhoods where Missing Middle Housing exists. The Missing Middle types have compatible forms, but often vary dramatically in their densities, thus making them impossible to regulate with a density-based system. For example, a bungalow court can have densities of up to 35 dwelling units per acre even though the buildings are only one story tall and the size of each cottage is only 25 feet by 30 feet. So if a zoning district sets a maximum density of 20 dwelling units per acre it would not allow the bungalow court type, but if the zoning district has a maximum density of 35 dwelling units per acre with few or no additional form standards every builder/developer will max out a lot with a large, out-of-scale apartment building. Also in these medium density zone districts, as the lots get larger buildings typically get larger as opposed to a form-based approach that would require multiple smaller buildings once a lot reaches a certain size (frontage width in particular).

In addition, density-based zoning treats all units the same regardless of size the same. This means that 3,5000 square foot unit is seen as the same as a 600 square foot unit in terms of density calculations, parking requirements, and other requirements such as open space, thus discouraging smaller units, which is exactly what the market needs and wants.

The Alternative: Form-Based Coding

Form-Based Coding has proven to be an alternative to conventional zoning that effectively regulates Missing Middle Housing. Form-Based Codes (FBCs) remove barriers and incentivize Missing Middle housing types in appropriate locations of a community.

FBCs represent a paradigm shift in the way that we regulate the built environment, using physical form rather than a separation of uses as the organizing principal, to create predictable, built results and a high-quality public realm. And, these codes are not mere guidelines and replace the zoning.

The Form-Based Approach to Regulating Missing Middle:

The approach to regulating for diverse housing within a neighborhood (blended densities) starts with an approach that uses density as an output not an input like conventional zoning does. As part of the early Community Character Analysis phase of a planning and Form-Based Coding project, a range of housing types appropriate for the community at large is created based on the community’s existing physical patterns, climate, and other considerations.

Then for each form-based zoning district a specific range of housing types is allowed. For example, in a T3 Walkable Neighborhood a single-family detached type, bungalow court, and side-by-side duplex may be allowed, or a urban T4 Urban Neighborhood zone would allow bungalow courts, side-by-side duplexes, stacked duplexes, fourplexes, and the multiplex: small type, even though the densities of each of these types can range dramatically.

Each type has a minimum lot size and maximum number of units allowed, thus enabling a maximum density calculation as the output.

In addition for each type, there are typically supplemental form standards that are regulated. For example a bungalow court allows for more units, but typically has a maximum height of 1–1.5 stories, a maximum building footprint and/or units size of around 800 square feet and a minimum size of courtyard. So on a 100’ by 100’ lot a bungalow court type is allowed that would integrates eight units in small, one-story units or two fourplexes would be allowed on the same lot.

FBCs represent a paradigm shift in the way that we regulate the built environment, using physical form and the Rural-to-Urban Transect rather than a separation of uses as the organizing principal, to create predictable, built results and a high-quality public realm. And, these codes are adopted into city or county law as regulations, not mere guidelines.

For more information about Form-Based Codes, see:

Or, contact us for questions of services in Form-Based Coding.

Form-Based Codes with Building Types to Reference:

  • Cincinnati, OH
  • Flagstaff, AZ (Chapter 10-40: Specific to Zones and Chapter 10-50. Part 4: Supplemental to Zones-Building Types
  • Mesa, AZ (Article 6: Form-Based Code)
  • Livermore, CA (Click on development code in upper left corner after clicking on the link)

What is the Transect?

The Rural-to-Urban Transect establishes a hierarchy of places and contexts from the most rural to the most urban. The designation of each zone along this hierarchy is determined first by the character and form, intensity of development, and type of place, as well as by the mix of uses within the area. This hierarchy of places becomes the framework for the entire FBC and supporting regulations for walkable urban areas.

Transect zones are used to reinforce existing or to create new walkable mixed-use urban environments. For more information on the Rural-to-Urban Transect visit www.transect.org.

“I want to thank you for your great work on Missing Middle Housing! It has been useful in my current research on policy reforms to support more affordable infill development in Victoria, B.C., and informing my report ‘Affordable Accessible Housing in a Dynamic City.'” — Todd Litman, Victoria Transport Policy Institute

Form-Based Code example
An example of the building types page from the City of Cincinnati Form-Based Code
Form-Based Code example
An example of a Transect zone from the City of Cincinnati Form-Based Code.
Form-Based Code example
Examples of the small multiplex building type from the City of Cincinnati Form-Based Code.
Model Transect for American towns
The model Transect for American towns is divided into six transect zones, each with a correlating number, higher numbers designate more urban zones, and lower numbers designate more rural zones: Natural (T1), Rural (T2), Sub-Urban (T3), General Urban (T4), Urban Center (T5), and Urban Core (T6).