Clear, accessible definitions for common urban planning terms.

What Is a Non-Conforming Use?

4 minute read

A non-conforming use is an existing building that would not be built under current land use regulations. While esoteric, the term is nonetheless critical to understanding the changes in development regulations over time.

Side-by-side brick duplexes pictured on a sunny day.

The stacked duplexes shown here in Omaha would currently be illegal to build in most U.S. zoning codes. | Missing Middle Housing

A non-conforming use is any building, structure, or other kind of development that would not be entitled or permitted under current land use regulation, but is allowed to remain in its existing form and function with restrictions on how it can be renovated or modified. 

Uses and structures may become nonconforming when rules and regulations, such as zoning codes, change, or when a property changes jurisdiction (such as by annexation or incorporation). Non-conforming uses are sometimes referred to as "grandfathered in," to borrow a phrase used commonly in non-planning contexts. In effect, non-conforming uses provide tangible evidence of how zoning and other development regulations change over time—in almost every historic U.S. city, non-conforming are commonplace and even highly valued. Missing middle housing—buildings ranging in size and density between a single-family detached home and a mid-rise apartment building, but built on a scale comparable to a single-family house—are one example of a common type of non-conforming use in relatively old neighborhoods in some U.S. cities.

Depending on the jurisdiction, the longer terms such as "legal non-conforming use" or a "legal non-conforming structure," can be used to describe the same critical concept: many zoning codes no longer allow the built forms and uses of history, and some land uses and developments out-live the regulatory environment under which they were built.

Regulatory Nuances

The definition of non-conforming uses can vary depending on the specifics of the zoning code (and building code) of a given jurisdiction. For example, zoning codes and other development regulations set a variety of limitations and conditions on the expansion, enlargement or intensification of a non-conforming use. 

With few exceptions, most non-conforming uses are allowed to persist only when stable in their present use, and the zoning code or other regulations will regulate or prohibit any expansion or enlargement of that existing non-conforming use. Once a non-conforming use has been abandoned, many zoning and building codes will prohibit the future resumption of the non-conforming use. To prevent non-conforming uses from descending to blight zoning codes generally allow for routine maintenance and repair—again, with specific limitations in place.

In some cases, an existing non-conforming use can be converted to another non-conforming use of “like nature"—if a planning authority determines that the change does not increase development impacts, such as traffic, parking, or noise. Authority to approve those changes varies by jurisdiction, but will usually require a site development permit (if the changes involve new buildings or structures) or a special use permit (if the change does not involve new construction). 

Renovations and other alterations of non-conforming uses that supersede the limitations and conditions set by each jurisdiction will require either zoning variances or other forms of discretionary approval to achieve entitlements. In such a case, the property would no longer be considered non-conforming—even if it varies from the zoning code, the project's entitlement would be current. Renovations or other alterations that bring the previously non-conforming use into conformity with the current zoning code could be approved as a by-right development.

Non-Conforming Uses and Zoning Reform

Multiple contemporary planning innovators, such as New Urbanists, YIMBYs, and smart growth advocates, will often cite non-conforming uses as an example of U.S. planning and zoning going to far in restricting the kind of historic building stock upon which many older U.S. cities were built—ensuring only car-centric planning, sprawl, and a perpetual lack of affordable housing options. Non-conforming uses are commonplace in historic urban areas, and, in many cases, are both highly-valued in the local housing market (i.e., historic residential neighborhoods are among the most expensive in the urban core of many U.S. cities) and a critical source of relatively affordable housing in some neighborhoods. 

These advocates argue that allowing the kinds of missing middle housing and other forms of residential density that were once common in cities would be one way to increase housing supply, including the supply of naturally occurring affordable housing, thus contributing to other desirable planning outcomes—such as reduced carbon emissions and increased access to jobs and public transit. Zoning codes should be changed, according to these advocates, to allow and provide incentives for more housing and building types that are now only available in finite supply in U.S. cities as non-conforming uses.

The YIMBY and New Urbanism movement cite non-conforming uses as a way for the history of urbanism could inform the future. The preceding and current era of planning, however, has been defined by planning policies that actively and thoroughly sought to ban and remove non-conforming uses. An APA Planning Advisory Service (PAS) report from 1949, for example, provided explicitly guidance on the use of planning tools to eliminate non-conforming uses. 

Despite some advancements for missing middle housing and other forms of zoning reform in recent years, most of the zoning codes in the United States block the construction of housing and building types that currently exist as non-conforming uses in some parts of the country.

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