Scope

• Zoning districts and their regulations are set by each local ordinance and differ widely. Always verify the municipal code's definitions and the current zoning and map for the project parcel
• Covers how districts are organized, how to read a district's use and dimensional tables, and how districts differ from building code occupancy groups
• Use-specific detail is in the permitted, conditional, and accessory uses note, and the dimensional controls are in their own notes

Terminology

• Base district: the primary zoning classification of a parcel, such as a single-family residential district
• Zoning map: the adopted map that assigns every parcel to a district
• Euclidean zoning: use-based zoning that separates land uses into districts; by far the most prevalent form in the US
• Performance zoning: zoning that regulates the effects of a use (noise, traffic) instead of listing uses
• Form-based zoning: zoning that regulates building form and the relationship to the street rather than use
• Incentive zoning: zoning that allows added height or density in exchange for public benefits
• Mixed-use district: a district that allows residential and commercial uses together
• Use table (use matrix): table listing uses against districts and showing whether each is allowed
• Dimensional standards table: table of lot size, setbacks, height, coverage, and floor area ratio by district
• Rezoning (zoning map amendment): a legislative change of a parcel's district

Classification

District families

• Residential: single-family, two-family, and multifamily districts, usually ordered from lowest to highest density
• Commercial: neighborhood, general, and downtown districts, from small-scale retail to large mixed uses
• Industrial: light and heavy industry, distribution, and manufacturing
• Agricultural: farming and rural districts
• Open space: parks, conservation, and institutional campuses

Codes and naming

• District codes often start with R, C, or I, but there is no consistent system; the same code can mean multifamily housing in one city, five units per acre in another, and 5,000 sq ft lots in a third
• Always read the district's purpose statement and its tables rather than inferring from its code

Mixing uses

• Strict use separation limits mixed uses in many cities; in a survey of 25 cities, less than 5 percent of land allowed mixed residential and commercial uses
• Mixed-use districts, form-based codes, and overlays are the usual tools for allowing mixed development

Requirements

Reading a district

A district's rules sit in two places:

1. Use table: lists each use and marks whether it is permitted by right, requires a conditional or special approval, is an accessory use, or is not allowed
2. Dimensional standards table: minimum lot area and width, setbacks, maximum height, maximum lot coverage, and floor area ratio, sometimes by building type

• Supplemental sections cover parking, landscaping, signs, fences, and standards for particular uses
• Footnotes to the tables modify the entries; read every footnote
• Overlay districts add or replace rules for parcels they cover

Zoning versus building code

• Zoning decides the use, location, and size of buildings; the building code decides how a building is built and made safe
• Zoning uses its own use categories (such as restaurant or office), while the building code classifies by occupancy group (such as A-2 or B); one use can map to different groups depending on size and occupant load
• A project meets both sets of rules, and zoning approval usually comes before building permit review

Worked examples

Reading a use table

An illustrative use table for three districts, with P for permitted, C for conditional approval, and a dash for not allowed.

Reading a dimensional table

An illustrative dimensional row for an R-1 district.

Coordination

• Survey and title: confirm the parcel's district on the official map and the lot area from the survey
• Planning staff: ask for a zoning verification or interpretation when the use is unusual
• Program: match the program's uses to the use table early, including accessory spaces such as home offices or detached units
• Overlays: check for overlay districts; they change both uses and dimensions
• Building code: classify the occupancy for each use at the same time; zoning use and occupancy group do not match one to one
• Future changes: pending rezonings and plan amendments can change the district during a long project

Common issues

• Assuming the code letter means the same thing everywhere: read the district purpose and tables
• Missing footnotes: footnotes change setbacks, heights, and allowed uses
• Confusing permitted and conditional: conditional uses need a hearing, time, and fees
• Ignoring overlays: a parcel in a base district may also sit in a historic, floodplain, or design overlay
• Treating a use as accessory: the accessory category has its own size and location limits
• Lot area differences: zoning may use net lot area after dedications while the survey shows gross area

Standards

• Local zoning ordinance and map: the controlling documents
• Comprehensive plan: the adopted policy that guides the district map

Sources

• Wikipedia: Zoning in the United States, https://en.wikipedia.org/wiki/Zoning_in_the_United_States
• Wikipedia: Special-use permit, https://en.wikipedia.org/wiki/Conditional-use_permit
• Wikipedia: Floor area ratio, https://en.wikipedia.org/wiki/Floor_area_ratio