Important Zoning Definitions NEED TO EDIT

1 Important Definitions


Accessory use/accessory dwelling unit

An accessory use is a structure or improvement that enhances or is required by the primary use of the lot. Accessory uses do not have to follow the same rules as structures permitted under conventional zoning, since they are not the primary purpose of the lot, and are usually much smaller and less noticeable than the main building. Examples of accessory uses include garages and vending machines.  

The most discussed accessory use of late has been accessory dwelling units (ADUs), also known as in-law suites, backyard cottages, or granny flats. Particularly popular following loosened restrictions in housing-starved West Coast cities including Vancouver, Portland, and Los Angeles, ADUs are small housing units built in the garage, attic, basement, or backyard of another building.

ADUs tend to be cheaper to build than a traditional housing unit—one study found that ADUs in the Pacific Northwest cost an average of $156,000 to construct, excluding land costs—and their more modest visual impact makes them an easier sell to change-averse neighbors. Rental income from an ADU can help homeowners afford to remain in increasingly expensive cities, or keep multi-generational families together. Still, ADUs remain bureaucratically difficult to build, if not completely illegal, throughout most of the country.


Also known as zoning categories or symbols, these letter-number combinations represent the nuts and bolts of what is and isn’t allowed on any given parcel in a city. There is no universal standard for zoning classifications, but many cities indicate the use with a letter or combination of letters (R for residential, C for commercial, and I for industrial, for instance), and the density or intensity of development with a number.

In addition to use and density, zoning categories also serve as shorthand for a number of key design requirements, including height limits, setbacks, and floor-to-area ratio (FAR), as indicated in the table below. Zoning classifications can be incredibly specific: Jacksonville, Florida, for instance, has 11 different categories for lowdensity residential parcels alone.

Euclid v. Ambler

The facts of the case: Ambler Realty owned 68 acres of land in Euclid, a Cleveland suburb. Euclid adopted a zoning code in 1922 that split the land into separate districts and prevented Ambler from developing some of it for industrial purposes. So the company sued, arguing that the zoning had significantly reduced the value of the land, and violated the Fourteenth Amendment’s protections of liberty and property.

In a 6 3 ruling, the court decided against Ambler, finding that the zoning ordinance did not exceed the local government’s power. While Ambler had hoped to develop industrial uses on its land, the decision was partly a referendum on the social value of apartments. “[V]ery often the apartment house is a mere parasite,” Justice George Sutherland wrote in his opinion, bringing “disturbing noises incident to increased traffic and business” and “depriving children of the privilege of quiet and open spaces for play.”


Exclusionary zoning

Even after the passage of the Fair Housing Act in 1968, zoning continues to be used to maintain racial and economic segregation by preventing less expensive types of housing, often in desirable neighborhoods. Requirements such as large lot sizes and parking minimums make it hard or impossible to build smaller, less expensive housing that middle- and lower-income residents would be able to afford. This often translates to a neighborhood’s high-quality public schools and proximity to jobs being “off limits” for people without the means to buy in. So exclusionary zoning works to concentrate poverty in areas that lack such strict rules.

Floating zones

Floating zones are a type of spot zoning that change the zoning laws for a particular area with conditions that “float” until a developer proposes a plan that can meet those conditions. Floating zones can be used to encourage specific types of land uses in a particular area, including affordable housing, commercial districts, or environmentally friendly developments.

Floor area ratio (FAR)

Floor area ratio (FAR), or the ratio of floor area to lot area, is a metric for regulating the number of square feet that can be developed on a parcel without specifying the exact shape and size of the structure. For example, a FAR of 5.0 means that a builder can develop five times as much square footage as exists on the lot. FAR is a metric within a rubric known as performance zoning, which includes other dimensional ratios to preserve open space, light, and air.

FAR requirements do not by themselves prescribe a particular building shape. A parcel with a FAR of 1.0 could include a two-story building covering 50 percent of the lot area, or two two-story buildings each covering onequarter of the lot.* These requirements often exclude basements, attics, and parking garages, and are usually coupled with more specific regulations pertaining to setbacks and height.

FAR is particularly relevant in New York City, where it is part of the formula for determining the transferable development rights, commonly known as “air rights,” for new towers. If a lot is currently improved with a building smaller than the allotted FAR, the owner of that building can sell those air rights—or excess FAR—to the developer of an adjacent property. By cobbling together air rights from other properties, a developer can build much higher than the allotted FAR on their lot.

This “cap-and-trade” system has been a driving force in the development of supertall towers in Manhattan. Critics of these policies have released a series of reports called “Accidental Skyline,” which criticize the city’s policies for supertall towers, like by-right approvals and the mechanical voids loophole, which the city recently reformed.

Form-based code

Rather than focusing on land use, form-based zoning codes regulate design elements, including the size, style, and placement of buildings. Form-based codes tend to promote walkability and more compact development patterns, since they allow different land uses to be closely intermingled.

Whereas Euclidean zoning often deals in minimums or maximums—like maximum height limits or minimum setbacks or parking requirements—form-based zoning is more prescriptive, requiring specific ranges for height, bulk, setbacks, and even more minute design details like signage, landscaping, and architectural ornamentation. Form-based zoning has been championed by New Urbanist architects and planners, who are interested in creating denser pedestrian neighborhoods, often with a traditional architectural vernacular.

Denver’s zoning code includes several “neighborhood contexts,” including suburban, urban edge, urban, general urban, and urban center. They are distinguished by building placement and height; “street, alley, and block patterns;” and “diversity of mobility options.” The adoption of these form-based codes in 2010 did not eliminate Euclidean codes: Of the city’s 25 neighborhood-context districts, 12 are exclusively residential, according to Sonia Hirt.

Incentive zoning

This permits greater density, fewer parking spaces, and other developer perks in exchange for contributions to the public good, like parks, transportation infrastructure, or affordable housing, as in inclusionary zoning policies. Incentive zoning can be used to guide developers to certain outcomes without making them legally mandatory. Successful incentive zoning usually requires land values to be sufficiently high for developers to be willing to incur additional costs.

Inclusionary Zoning (see Incentive zoning)


Minimum lot size (see Lot coverage)


Mixed-use zoning (see History)


Lot coverage

Lot coverage is the bird’s-eye-view footprint of a structure—in other words, the proportion of its lot that it covers up. Unlike FAR regulations, lot-coverage rules do not regulate the livable square footage of a building, but rather how much space it takes up at ground level.

Lot-coverage maximums mandate that a development’s footprint cannot exceed a certain percentage of the lot. In the affluent Bay Area suburb of Tiburon, for example, houses in R1 zones can only cover 30 percent of the lot. These restrictions maintain a semi-rural character in many suburban neighborhoods, and can also provide environmental benefits related to fire protection and water drainage.

Similar to lot-coverage maximums, minimum lot sizes are in force in many suburban neighborhoods and towns wishing to preserve a natural feel. Parts of Greenwich and Stamford, Connecticut, have minimum lot sizes of three acres or more. Despite providing some environmental benefits, these kinds of restrictions have the effect of increasing car dependence by ensuring buildings are far apart from one another; they have also been criticized for being a tool of segregation, wherein all potential residents must be able to afford a massive lot.

Nonconforming use

A nonconforming use is a structure or design element that is not legal under current zoning. Many nonconforming uses—like an apartment building in a neighborhood that was zoned for lower density, or a store in an exclusively residential zone—are grandfathered in. But if a building is destroyed, whether by demolition or disaster, itcan’t always be rebuilt to the same density or for the same use.

ADUs are a common nonconforming use that is increasingly being legalized. In some cities and states that have relaxed ADU rules, property owners with previously nonconforming ADUs can pay a fee, get their property inspected, and get it legalized.

Overlay zone

An overlay zone or district enacts special zoning rules in a designated area that supersede or alter the existing zoning. Usually, overlay zones are more strict than the existing zoning and are intended to protect sensitive local environmental or design features. For example, overlay zones can be implemented in flood-prone areas, adding special vegetation requirements or impervious surface maximums.

Parking minimums

Parking minimums are the number of off-street parking spaces required for a new development. Different uses trigger different parking requirements: In Los Angeles, the first city in the nation to adopt parking minimums, yms, restaurants, nightclubs, and coffee shops must provide one off-street parking spot per 100 square feet. Single-family homes require two off-street spots, and apartment buildings with more than three units must include one parking spot per unit. However, various incentive-zoning policies and special zoning districts make these requirements fungible in many circumstances.

Parking minimums began popping up in the 1920s and ‘30s when the availability of parking started to become a major issue in cities. These laws, which exist in virtually every city with a zoning code, have remained largely unchanged until recently, when a convergence of trends has caused cities to rethink their efficacy.

In expensive cities, the $25,000 to $50,000 for each off-street parking spot only serves to make housing more expensive while limiting the amount of space that can be devoted to housing. And in dense urban areas, the rise of ride-hail apps, car-share, and bikeshare, combined with good old-fashioned walking and transit, have made personal car storage a less urgent issue.

As “a fertility drug for cars,” in the words of UCLA professor and parking guru Donald Shoup, parking minimums induce demand for driving, amplifying all of the other challenges associated with cars, including traffic, safety, and greenhouse gas emissions.

San Francisco made national news last year when it eliminated parking minimums, but Hartford and Buffalo had quietly done so the year before. (Many cities have eliminated parking minimums in downtown neighborhoods an other special districts, but not throughout the entire city.) In Sandpoint, Idaho, the developer of a three-story office building realized it would be more cost effective to buy and demolish neighboring historic commercial buildings to accommodate the project’s required 218 off-street parking spaces than to include them in the new building, according to the organization Strong Towns. The events in Sandpoint caused the city to revise its parking minimums, enabling at least four new developments that would not have been allowed under the previous rules.

Performance zoning (see Floor area ratio)


Planned unit development (PUD)

Planned unit developments are developments that are not subject to standard “by right” zoning, but are allowed greater flexibility by the local government. Developers may submit a project as a PUD to be able to build more densely or on a challenging parcel of land, in exchange for providing community benefits such as affordablehousing units or a park. In Washington, D.C., PUDs have taken off in recent years, and so have lawsuits aiming to block them.


Setbacks are the minimum distance a structure must be from the edges of the property line. Not to be confused with setbacks as an architectural element (like those that became popular in New York City following its 1916 zoning ordinance), setbacks in zoning parlance are a key part of the ground-level experience of the city. Setbacks provide a sense of uniformity to a city block, and ensure that windows receive adequate light and air. As is the case in many jurisdictions, Santa Clara County, California’s setback requirements include exceptions for elements like awnings, bay windows, decks, basement light wells, and ADA-accessible infrastructure. R1 singlefamily home zones with 5,000-square-foot lots in unincorporated Santa Clara County or in cities without their own zoning ordinance have front and rear setbacks of 25 feet apiece, and side setbacks of five feet.

Spot zoning

Spot zoning is a negatively charged phrase that refers to a rezoning for a particular parcel or project that does not conform to a city’s zoning code. It gives developers a way around the long and arduous process of changing the zoning ordinance. Critics see spot zoning as a corrupt strate y to bypass traditional planning processes and provide special advantages to favored developers. Instances of spot zoning have often been successfully challenged in court, according to Hirt: Legislators have to prove that such zoning changes are in the public interest, and must be compatible with the existing zoning code in its impact on the community, if not according to its design specs.


Upzoning is the rezoning of land to allow for more intense use (e.g., a higher FAR) or a change in use (e.g., from residential to mixed residential/commercial). It is often framed as a strate y to combat exclusionary zoning. Minneapolis eliminated R1 zoning in its 2040 plan, allowing residential buildings of up to three units in all residential areas, and Oregon just passed a similar statewide law. California’s SB50, an upzoning bill that prioritized transit and employment hubs for more density, stalled out in the state legislature this May. (Want less density? That’s downzoning.)


A variance is a zoning change that is granted to a developer by a government body on a discretionary basis, often following public hearings. Developers might ask for relief from certain requirements, citing project-specific financial or practical difficulties. Variances are often related to architectural details. One Chicago apartment developer recently requested a variance to exceed the parcel’s height limit by 6 feet to include higher ceilings in the five floors of apartments below.

Source: Schneider, B. (2019, August 6). How to Understand Municipal Zoning Codes. Bloomberg.Com.



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