Overlay zoning districts can be a valuable tool
Overlay zoning districts is a valid tool in some conditions. But be careful not to overuse it when more traditional zoning techniques can do the job.
A zoning ordinance will always include a zoning map that shows the municipality, or county, divided up into zoning districts. There may be residential, commercial, office, industrial, rural residential, and working lands (agriculture, forestry) zoning districts. Each zoning district has its own distinct list of permitted uses, special uses, and regulations. For example, a residential district may include dwellings and duplexes as permitted uses; apartment buildings as possible special uses; and other regulations such as minimum parcel size, setbacks, building height, and so on.
An overlay zone would be an additional zoning district that is laid over the top of two or more zoning districts – usually to introduce an additional standard(s) or regulation(s) along some feature. It is a second layer of district(s) on top of the zoning district map. Think of the standard colors of a zoning map illustrating where different zoning districts are located. Then think of a transparent plastic sheet laid on top of the zoning map, showing an additional boundary, to illustrate the overlay district.
In the zoning ordinance, the overlay district text might have additional, or different, regulations that apply within the overlay district shown on the zoning map. For example, an overlay district along the entire length of a river, that flows through several different zoning districts, may require a vegetation buffer and larger setback from the riverbank. The overlay district text in the zoning ordinance is where the larger setback and requirement for the vegetation buffer is written. The alternative would be to add those two regulations into each underlying zoning district – often making it necessary to have the same text in the zoning ordinance several times, once for each zoning district the river flows through.
The overlay district tool can be used for several different things. It can be an overlay around an airport (height restrictions along the runway approach); municipal wellhead protection zones (around public water supply wells to prohibit certain polluting activities, to have stricter secondary containment to protect area from accidental spills); both sides of a river or lake; vegetation buffer areas; greater setbacks (along/around a lake shoreline, high risk erosion setbacks); DNR Critical Dune additional regulations; beach protection; along a scenic road or highway (aesthetic regulations, greater setbacks); historic districts (facade plan reviews, historic integrity/preservation regulations); commercial corridor (driveway access management, landscaping standards); and more.
Common standards or regulations in an overlay zone may include building setbacks, density standards, lot sizes, impervious surface reduction, vegetation requirements, and building floor height minimums. Modification of the list of permitted uses or possible special uses is normally not a part of an overlay zone. There is increasing interest in using overlay zones for utility-scale renewable energy. A handful of Michigan communities adopted solar overlay zones, based on an evaluation of factors such as slope, ground cover, soil types, and the absence of wetlands/forests. Huron County was the first in Michigan to adopt a wind energy overlay zone.
An overlay zoning district is a zoning tool that can work well for certain situations, but maybe best avoided for other situations. If a proposed overlay district is only on top of one underlying zoning district, then creating an overlay district may not be the best approach. If it only affects one zoning district, then the additional text can just be added to that one zoning district. Adding it to the existing underlying zoning district is less work and makes for a more streamlined zoning ordinance. If the overlay is on top of two or more underlying zoning districts, then creation of the one overlay district may be less work than amending two or more underlying districts and makes for a more streamlined zoning ordinance.
If the regulation being thought about for a proposed overlay district is about changing the types of permitted uses, or possible special uses, then it may be more appropriate to create a new underlying zoning district for that territory. This is a judgement call, but usually when creating an area with different uses that will be allowed, it should be within its own underlying zoning district. An example of this would be a territory along a river that has very unique characteristics – such as a wide river valley, lots of wetlands, geologic features, and so on. The land along the river is more than just a ribbon along both sides of the river, it includes much more territory. That area deserves its own unique parcel sizes, setbacks, and specific list of permitted uses and special uses. That describes a new underlying zoning district, not an overlay district.
In another scenario, an overlay district around public water well would be drawn to mimic the area around the well where contaminants from the surface of the ground could move into the drinking water of the municipal water system. Often this overlay district will have additional site plan review requirements for secondary containment of chemicals, no ground discharges, and may prohibit some high-risk land uses that would otherwise be allowed in the respective underlying zoning districts. This example may be a situation where an overlay district does include modification of what the allowed land uses are. This would be the appropriate exception, not the rule.
Michigan State University Extension land use educator provide various training programs on planning and zoning, which are available to be presented in your county. Contact your land use educator for more information.