Zoning ordinances, the most prominent form of local land use regulation, are laws that group compatible land uses together. These ordinances may preserve quiet and safety in residential areas, minimize and manage traffic, reduce fire risks, maintain open space and views . . . you get the idea.

A typical zoning code has two parts: a textual ordinance that specifies the regulations for all the different zoning district designations and a zoning map that shows the zoning district designation for each parcel of land throughout the city or county.

Zoning ordinances traditionally regulate the following:

  • Use: They limit the uses permitted on certain land.

  • Height: They limit the size of buildings on the land.

  • Bulk: They limit the size of lots and the placement of buildings on those lots.

Modern zoning regulations may include other types of restrictions as well, such as architectural design regulations that are intended to ensure new buildings are architecturally compatible with existing buildings in the area.

The terminology may vary, but a typical zoning ordinance designates residential, commercial, industrial, and agricultural zoning districts. Within each of these categories, an ordinance may include a number of different zoning designations with increasingly permissive use restrictions. For example, a simple zoning ordinance may contain the following residential districts:

  • An R1 zoning district allowing only single-family homes

  • An R2 district allowing one- or two-family homes

  • An R3 district allowing multiple-family dwellings

An ordinance may further refine these zoning designations by specifying different height and bulk limitations in different zones. Common bulk limitations include

  • Floor-area ratio (the ratio of floor space to lot size)

  • Minimum floor space

  • Minimum lot size

  • Requirements that buildings be set back a minimum distance from lot boundaries

An ordinance may specify several zones allowing the same uses but with different combinations of height and bulk restrictions. For instance, it may specify an R1-21 zone that allows single-family homes on lots no smaller than 21,000 square feet.

The traditional zoning ordinance is cumulative, meaning that higher uses (those that are less intensive and less likely to be objectionable) are allowed in lower-use zones. For example, a single-family house may be built in a commercial zone, but a commercial building may not be built in a residential zone.

However, modern ordinances commonly make uses noncumulative or exclusive, meaning that higher uses aren’t allowed in lower-use zones. For example, even if they want to, landowners can’t build single-family houses in a noncumulative or exclusive commercial zone.