Overlay Zoning

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How it Works
Implementation
Where It's Been Done
Advantages and Key Talking Points
Challenges

Excerpt of the floodplain overlay from the Garfield County overlay districts map Overlay zoning is used by communities to apply area-specific standards and/or conditions. A base zoning district (such as residential or mixed-use) determines the types of uses permitted and the minimum dimensional requirements of lots and buildings. An overlay district (or overlay zone) applies an additional layer of standards to all areas within a defined overlay boundary, regardless of the underlying base zoning district. For example, an area with single-family homes that is zoned R-1 might also be within a hillside overlay zone. In this example, the permitted uses might allow construction of a single-family home according to the R-1 standards; however, the hillside overlay zone might prevent construction without first obtaining a geo-technical report.

Implementation

To implement an overlay zoning district, many communities first prepare a study or report identifying a problem and linking the benefits of an overlay district to broader community policies or objectives in the comprehensive plan. Often, and particularly in the case of natural hazard mitigation, overlay zoning requires technical analysis and mapping (spatial definition) of the hazard boundary. The community then prepares the ordinance to include standards and procedures that apply to that defined overlay. As with other zoning code amendments, adoption of the ordinance requires approval by the governing body (City Council, Board of Trustees, or the County Commissioners). Overlay districts also can be amended, expanded, and lands reclassified through the rezoning process.

Where It's Been Done

Douglas County adopted a Wildfire Hazard Overlay District as part of their zoning resolution. The first item listed in the purpose statement for the district is “to develop and maintain a map of Douglas County that allows for preliminary identification of Wildfire Hazard Areas.” The regulations and procedures within the overlay district not only apply to those included on the overlay map, but also any land areas field-verified as potential hazard areas. Within the overlay, land use applications must comply with general mitigation and forest management provisions, road and street design criteria, water supply provisions, and structural design elements.

Advantages and Key Talking Points

The primary benefit of overlay zoning is applying a unique set of standards to a specified area without having to amend all other relevant sections of the code. Other benefits include:

Provides additional protection for defined hazard areas without negotiating on a case-by-case basis.
Allows existing zoning regulations to be superseded or complemented to solve a known problem.
Can implement comprehensive plan policies and strategies associated with future land use and the environment.
Relatively easy to maintain over time following initial adoption.

Challenges

Overlay zoning often requires a higher level of technical expertise to administer. For example, enforcement of a floodplain overlay requires detailed knowledge of technical FEMA and NFIP requirements and other local building and engineering requirements. Other challenges include:

Can require trained planning and engineering staff to develop the initial maps and standards.
Adds an additional layer of requirements to the development review process.
To mitigate natural hazards, requires fairly technical mapping of hazard area.
Requires a zoning amendment, which requires formal action by the governing body.
Requires that a community have a zoning ordinance in place, which may present a challenge to some smaller communities in Colorado without zoning.