In the early twentieth century, American cities looked much different than they do today. In heavily urbanized areas, houses, shops, and factories could often be found on the same block, and many city-dwellers spent their time in overcrowded buildings that suffered from poor natural lighting.
While mixed-uses meant that most cities were more walkable than they are today, that same proximity created health and safety hazards for urban residents. Pollution was rampant, streets were dangerous, and noisy bars and factories disturbed nearby apartment-dwellers late into the night. Outside the industrial cities, new suburbs were being developed rapidly, marketing peace and quiet to draw residents out to the countryside. The architects behind these new communities hoped to create neighborhoods that would stand the test of time, but they worried how they could safeguard these areas from reproducing the same health and safety hazards that prevailed downtown.
The tool these planners, developers, and architects ultimately created was the zoning code. By strictly defining what can and cannot be built in different areas, and establishing unified development standards for residential, commercial, and industrial districts, zoning codes enabled these new communities to more harmoniously distribute land uses across space, and to confine hazardous uses to areas more physically removed from residential neighborhoods.
Today, zoning codes remain common practice in community development. Because zoning is a local process, tailored to the unique needs, circumstances, and aspirations of each municipality, numerous varieties of codes have developed over the years as communities have independently attempted to address these concerns. Despite these variations, most zoning codes may be classified into one or more of the following broad categories: EUCLIDEAN ZONING, PERFORMANCE / IMPACT ZONING, INCENTIVE ZONING, FORM-BASED ZONING, and HYBRID ZONING.
The most common form of land-use regulation in the United States is known as Euclidean zoning. Euclidean zoning is not, in fact, named after the eminent Greek mathematician, but rather after the Village of Euclid, Ohio, where in 1926, a development company famously challenged the constitutionality of the local zoning code. Euclid’s code had placed height and use restrictions on different zones, and the developer argued that by limiting what could and could not be built on undeveloped property, the code had unfairly reduced the value of its landholdings.
In a landmark decision, the U.S. Supreme Court ruled in favor of the local government, declaring that zoning codes are a valid extension of a city’s right to regulate land uses in the name of protecting public health, safety, and welfare (Village of Euclid, Ohio v. Ambler Realty Co., 272 U.S. 365 (1926)). Because Euclid’s code had segregated different land uses, with housing in one place, shops in another, and factories elsewhere, communities nationwide began following the Euclidean model, believing it to be the most effective way to meet the health, safety, and welfare clause. The Euclidean format soon became standard zoning practice.
As part of isolating ‘incompatible’ uses, Euclidean codes sort possible land uses into broader categories, usually classified agricultural, residential, commercial, industrial, institutional, or open space. For example, the ‘candle manufacturing’ use is identified as an ‘industrial’ use, and is thus only allowed to take place in industrial zones. Each zone has its own height, setback, parking, landscaping, and building volume restrictions that vary with intensity. For instance, low-density residential areas tend to cap the height of houses at two-stories while high-density residential zones may allow apartment towers up to twenty-stories or more in height.
Some uses are permitted ‘by right,’ meaning they require no special review from city staff, while others are designated ‘conditional’ uses that require a public hearing in which special conditions are created to address a project’s unique impacts.
While Euclidean zoning has enabled cities to avoid unnecessary noise, glare, and pollution impacts resulting from the incompatible placement of uses, some communities have sought alternatives to Euclidean codes, perceiving that they have a tendency to produce cities where most trips must be made in a private vehicle, and where the mixed-use neighborhoods that 21st century Americans have come to expect, are discouraged.
PERFORMANCE / IMPACT ZONING
Often using Euclidean zones as a foundation, the Performance and Impact zoning techniques enable more unusual land uses to move into existing zones if they conform to a fixed set of standards established for that district. Differing land uses produce varying external impacts, ranging from traffic and noise to glare and waste generation. Under impact zoning, performance standards are established to manage those impacts and better promote compatible development. For instance, a gym might be able to open in a medium-density residential area if it closes at 9pm, is only one-story in height, and will not push traffic levels above an established, acceptable threshold.
Another technique – performance zoning – uses a variety of dimensional ratios to regulate land-use intensity. Examples may include floor area ratio or ‘FAR’ (the ratio of building floor area to lot area), open space ratio (the ratio of open space to overall site area), and livability space ratio (the ratio of non-vehicular space such as lawns or landscaping to total site area). These are often used to address specific site impacts, from shading and open space quality to the size and placement of parking lots.
Although performance and impact zoning move away from stringent land-use separation, they do so by requiring greater time and monetary inputs. Many of the performance standards require sophisticated measurement techniques that staff must be trained to use. Moreover, these standards tend to have little direct relationship to the look and feel of resulting development. For example, a site with a permitted 1.0 FAR could contain a 2-story building that covers half the site, or a 4-story building that occupies a quarter of the site. Residents that may have expected shorter buildings from this 1.0 standard may be disappointed with the results. For these reasons, the impact zoning approach is typically selectively applied in certain districts, or else combined with other zoning approaches, rather than implemented as a standalone practice.
Like the previous techniques, Incentive zoning uses Euclidean zoning as a baseline. Yet to permit greater diversity and flexibility within those Euclidean zones, incentive zoning enables projects to exceed standard requirements if they provide some form of benefit to the local community. For example, in exchange for providing amenities (like parks, plazas, transit access, public art, or affordable housing), projects are usually allowed to build at higher densities or to greater building heights than are typically allowed. In many cases, this balancing act between development and community improvement occurs through a discretionary process that attempts to match the intensity of additional development to the scale and quality of the benefits provided. This can require significant staff time to determine.
One of the newer interpretations of land-use planning, Form-Based zoning regulates development by focusing on the scale, design, and placement of buildings, paying particular attention to their relationship with the street (or other public spaces). Communities that implement form-based zoning codes tend to believe that both the look and arrangement of buildings more strongly define a community’s character than do the actual uses that take place within those buildings. Because they focus on form influencing function, these codes tend to be employed to promote walkability, transit-friendly development, and more compact settlement patterns.
Form-based codes involve prescriptive development standards that may include minimum and maximum setbacks (or ‘build-to lines’), desired proportions for buildings and entryways, and requirements to conceal on-site parking. As such, they represent a significant departure from traditional Euclidean zoning standards.
For example, while a Euclidean district might prohibit buildings from locating closer than 15 feet from the street, a form-based code might require that buildings be located within 5 and 8 feet of the street. While a Euclidean district usually has maximum height limits, a form-based code operating near a transit station might require a minimum height or intensity-level for all new buildings, prohibiting single-family homes from being built on lots more suitable to four-story apartments. Another departure from Euclidean zoning is the highly visual nature of form-based codes, which rely more on 3D imaging and detailed drawings than do traditional codes.
Yet while these zoning innovations create new development opportunities, the highly prescriptive nature of form-based codes sometimes limits their effectiveness. Form-based codes often introduce new concepts or terminology that is unfamiliar to developers and civic administrators, prompting criticism and confusion. Additionally, in auto-dependent communities, there is often a mismatch between the ideals of the form-based code and the realities of existing infrastructure. Despite these challenges, and the fact that form-based codes remain a minority approach to zoning, they have gradually encouraged city governments to reexamine traditional codes, and implement new strategies for shaping community development.
Most modern zoning codes contain elements of the various approaches introduced above. They often employ traditional Euclidean zoning districts (especially in single-family residential areas) while applying performance zoning standards to more intensely-developed neighborhoods. They also tend to introduce incentive zoning to reduce parking and create affordable housing, while implementing form-based regulations in denser downtown areas. This modern practice of combining philosophies is often referred to as Hybrid zoning—an approach that identifies the best elements of each practice and integrates them into a new whole.
Modular (or ‘Composite’) zoning is a specific type of hybrid zoning. It takes three fundamental components of development—use, form, and orientation—and mixes and matches them to create a wide variety of zoning districts. The ‘use’ component establishes the types of land uses (residential, commercial, industrial, etc.) permitted within a zoning district, while the ‘form’ element delineates height limits, entryway typologies, façade design standards, and so on. Finally, the ‘orientation’ component defines how the site is arranged, with standards for where buildings are placed in relation to sidewalks, where landscaping and open space are provided, and where pedestrians are expected to access the site. Any combination of these components creates a zoning district, meaning that zones may be much more intensely customized to the unique needs of each community.