Miami’s new code, known as Miami 21, marks the first time a form-based code has been adopted for an entire major U.S. city, and it is likely to accelerate the trend.

The city of Miami, Florida, adopted a new zoning code last October for the entire city that is based on the urban planning principles of smart growth and new urbanism—however, the new code does not go into effect until May. Referred to as “form-based” zoning codes because they primarily regulate the shape of buildings and allow for a mix of uses, such codes are unlike most traditional zoning codes, which focus on separation of uses.

Form-based codes encourage architectural continuity by promoting better transitions between high- and low-rise areas, and promote walking by allowing more uses on the ground floor of buildings, more streetscape requirements, and more uses within walking distance of each neighborhood. (See “Community and the Form-Based Code,” June 2009, page 88.)

An emerging national trend, such codes have been adopted for many neighborhood master plans, greenfield developments, urban redevelopment areas, and smaller cities. However, the Miami 21 code marks the first time a form-based code has been adopted for an entire major U.S. city, and will likely accelerate the trend.

In addition to the substantive differences between form-based codes and current zoning codes, there are significant organizational differences, most notably ease of use and predictability. In contrast to traditional codes that often include decades’ worth of overlay districts and hidden exceptions, form-based codes typically have only six districts, often labeled T1 to T6.

A basic principle of form-based codes is that a gradual transition from wilderness to urban core— known as the “transect”—guides the placement of buildings. For example, multistory towers should not be placed next to single-family houses. Traditional codes often permit abrupt changes of scale because the primary focus is on separating uses.

This emphasis on gradual transition applies not only to the original zoning atlas, but also to future zoning amendments. Form-based codes typically provide that an area may be rezoned only to the next more intense district, and only if abutting such a more intense district. Known as “successional” zoning, this approach is designed to prevent “leapfrog” zoning, overlay districts, and hidden exceptions.

Such predictability, coupled with the simplicity of zoning districts, is a benefit to both residents and developers. Predictability discourages speculative land prices and manages residents’ expectations.

The principles underlying form-based codes include a corollary to the transect: that the gradual transition should occur along certain corridors, and that, in addition to the urban core, a metropolitan area may have several subcores, or nodes. Such corridors and nodes preserve the residential neighborhoods between them, support public transportation, and increase economic opportunity by locating more jobs and retail uses along transit routes.

Another principle of form-based codes is the notion that pedestrians should come first. While traditional codes ignore pedestrians, and thus encourage car use, form-based codes promote pedestrian activity in three primary ways:

  • Activation of lower floors. Form-based codes encourage active uses on the ground floor of every large urban building, discourage extensive blank walls, encourage frequent doors and windows, and require parking to be concealed behind screens or active spaces.
  • Increased streetscape requirements. While streetscape improvements traditionally occur on public land, form-based codes often require private developers to implement certain elements of pedestrian-friendly streetscapes, such as wider sidewalks and shade trees.
  • Greater mix of uses. Form-based codes allow for a wider mix of uses in high-density areas, thus promoting pedestrian accessibility and reducing the need for automobile trips.

In spite of the many purported benefits of form-based codes, there are risks associated with large-scale rezoning efforts, including the following:

  • Loss of development rights. Although cities often try to maintain similar development intensity before and after adopting a form-based code, the related increase in design requirements, such as additional setbacks above lower floors, may reduce development rights.
  • Vague provisions and unfamiliarity. Because form-based codes are generally uncommon, city planning staff may be unfamiliar with the new vocabulary and some glitches will inevitably be encountered.
  • Limited increases in zoning rights. Because form-based codes are firmly founded on the idea of the transect and successional zoning, they can limit developers’ ability to achieve major increases in zoning rights after acquiring a property.