Ohio ADU Laws: Zoning, Permits, and Local Restrictions

Ohio ADU laws aren’t found in a single state statute. Ohio has no statewide rule that either authorizes or prohibits accessory dwelling units, so whether you can add one to your property, how big it can be, and what approvals you’ll need are decided entirely at the local level. A lot in Cincinnati may qualify under a straightforward city ordinance while a similar lot in an unincorporated township ten miles away allows no second dwelling at all.

Why the Rules Are Local

Municipal control over ADUs traces to Article XVIII, Section 3 of the Ohio Constitution, the home-rule provision that lets cities and villages adopt local police, sanitary, and similar regulations as long as they don’t conflict with state law.¹ Each city council or village board writes its own zoning code defining whether ADUs are allowed, where they can go, and under what conditions. Ohio Revised Code Chapter 713 sets out how municipalities create planning commissions and gives those commissions authority to approve or deny proposed structures and uses.² Your planning commission is the body that will actually review your application.

If your property sits in unincorporated territory rather than inside a city or village, a different statute controls. Ohio Revised Code Section 519.02 authorizes township boards of trustees to regulate the location, size, and use of buildings in unincorporated areas, including lot coverage, setbacks, and density.³ Township residential zoning is often more restrictive than nearby city zoning, so a neighbor’s approval across a municipal line doesn’t tell you what your township allows.

Which Ohio Cities Currently Allow ADUs

Most Ohio cities still don’t permit ADUs. Among those that do, the rules and approval paths differ substantially:

Cincinnati allows ADUs in most zoning districts without a conditional use hearing. The property owner or a designated “responsible person” must live on the property, a restrictive covenant must be recorded with the Hamilton County Auditor, and violating the occupancy requirement carries a $15,000 fine.⁴
Columbus passed Ordinance 2526-2025 in November 2025, launching a pilot program focused on adding affordable ADUs to lots with one existing single-family home.⁵
Westerville permits ADUs by right in the Olde Westerville Special Overlay District. All other residential districts require a conditional use permit, the maximum size is 720 square feet, the owner must live on the lot, and a recorded covenant is required.⁶
Dayton permits ADUs in single-family districts through a conditional use process.
Lakewood allows ADUs with a building permit and requires separate utility taps for water, sewer, and storm connections.⁷

Yellow Springs and Bowling Green also have ADU ordinances. If your city isn’t on this list, start with your local zoning office. The answer might be a flat “no,” or it might be “yes, but only through a conditional use permit,” which is a meaningfully different situation.

What Local Codes Typically Require

Even where ADUs are permitted, local codes impose physical and occupancy standards to keep the second unit subordinate to the main house. The categories look similar across jurisdictions; the numbers don’t.

Size, Height, and Setbacks

Most ordinances cap ADU floor area. Westerville limits ADUs to 720 square feet.⁶ Other jurisdictions set the ceiling at 800 or 1,000 square feet, or peg it to a percentage of the primary home’s area. Height limits for detached ADUs typically run around 25 feet; Cincinnati measures that to the midpoint of the highest gable for pitched roofs and to the top of the cornice for flat roofs.⁴ Detached ADUs usually have to meet the same setback standards as other accessory buildings on the lot, and some codes also require the unit to sit behind the main house.

Owner Occupancy

Many Ohio cities that allow ADUs require the property owner to live in either the main house or the ADU. Cincinnati and Westerville enforce this through a restrictive covenant that must be recorded with the county.⁴⁶ Not every jurisdiction takes this approach. Dayton and Yellow Springs do not impose owner-occupancy. Check your local code before assuming you can build purely as an investment rental.

Parking and Utilities

Parking rules vary between neighboring cities. Westerville requires one additional off-street parking space per ADU.⁶ Cincinnati exempts ADUs from off-street parking requirements entirely, though existing parking required for the main house must stay in place.⁴

Utility connections differ too. Lakewood requires separate water, sanitary sewer, and storm taps for each ADU, meaning individual connections to the city’s lines rather than running off the main house’s plumbing.⁷ Other cities allow shared connections. Separate utility taps typically cost several thousand dollars, so confirm this early.

By-Right Approval vs. Conditional Use Permits

In cities where ADUs are permitted by right, you file for a zoning certificate, meet the physical standards, and move on to the building permit. In cities where ADUs aren’t allowed by right, you’ll need a conditional use permit, which is a heavier lift because it requires a public hearing before the planning commission or zoning board.

A conditional use application includes a site plan, a legal description of the property, and a statement explaining why the proposed use fits the neighborhood. The commission then evaluates whether the ADU would be compatible with the surrounding area, adequately served by public infrastructure, and not detrimental to neighboring property values. Some cities require applications to be filed at least 30 days before the hearing date. If neighbors object, the process can turn adversarial, and approval isn’t guaranteed even when your plans meet every physical standard. The commission retains discretion to deny an application it finds would change the essential character of the area.

The Building Permit and Inspection Process

Once you’ve confirmed your zoning district allows the ADU, either by right or through conditional use approval, the construction side requires a building permit from your local building department. Lakewood requires separate building, electrical, plumbing, and mechanical permits.⁷ Cincinnati routes everything through its Department of Buildings and Inspections.⁸

The documentation package generally includes a site plan showing all existing structures and the proposed ADU location with distances to property lines, exterior elevations, and plans showing how utilities will reach the unit. Some cities also require landscape plans, color renderings, and specifications for exterior materials. Filing fees range from under $100 for a simple zoning certificate in some townships to several hundred dollars for a full building permit.

Ohio law requires building departments to review permit applications within 30 days of submission.⁸ In practice, initial reviews often come back with correction requests, and the 30-day clock restarts each time you resubmit revised plans. Budget for back-and-forth, and longer if your building department is backlogged.

Residential permits in Ohio are reviewed against the Residential Code of Ohio rather than the commercial building code. During construction, inspectors visit at key stages to check foundation, framing, electrical, plumbing, and mechanical systems. After the final inspection confirms the completed structure matches the approved plans, the building department issues a Certificate of Occupancy. You cannot legally allow anyone to live in the ADU until that certificate is in hand.

HOA and Deed Restrictions Can Still Block You

Clearing your local zoning office doesn’t guarantee you can build. If your property is subject to a homeowners association or recorded deed restrictions, those private covenants can independently prohibit ADUs. Unlike California, which has passed laws preempting HOA interference with ADU construction, Ohio has no such statute. A restrictive covenant banning secondary dwellings on your lot is generally enforceable in Ohio courts even if your city’s zoning code allows ADUs.

Before spending money on architectural plans, pull your deed and review your HOA’s CC&Rs. Look for language restricting the number of structures on a lot, prohibiting rental activity, or limiting the property to single-family use. If you find restrictive language, your options are negotiating an amendment with the HOA board or getting a legal opinion on whether the specific covenant is enforceable as written.

Property Tax and Insurance Consequences

Adding an ADU increases your property’s assessed value and therefore your property taxes. Ohio county auditors conduct full reappraisals on a six-year cycle with a triennial update in between, but new construction typically triggers a reassessment outside that schedule. The auditor’s office will generally value the ADU based on construction costs and add that figure to your existing assessment. Ohio assesses residential property at 35% of market value, so the increase to your tax bill depends on your local millage rate and the auditor’s valuation approach. Ask your county auditor’s office for a rough estimate before you break ground.

Your standard homeowner’s policy may not automatically cover an ADU, particularly a detached structure or one you plan to rent. Many policies include “other structures” coverage set at around 10% of your dwelling coverage, which often isn’t enough to rebuild a detached ADU after a fire or storm. Basement conversions and additions above an attached garage are more likely to fall under your existing dwelling coverage, but confirm this with your insurer before construction. Renting the ADU almost always changes the insurance picture; most carriers require a landlord endorsement or a separate landlord policy to cover tenant-related liability and loss of rental income. If the ADU has its own address or separate utility meters, some insurers classify it as a standalone structure needing its own policy.

If You Plan to Rent the ADU

Renting the ADU makes you a landlord subject to Ohio’s landlord-tenant laws. Ohio Revised Code Section 5323.02 requires owners of residential rental property to file registration information with the county auditor where the property is located.⁹ Failing to register can create complications during property transfers and tax filings. You’ll also need to comply with Ohio’s habitability standards, provide proper notice before entering, follow security deposit rules, and use the correct legal process for evictions. Some cities layer their own rental registration or inspection requirements on top of the state baseline.

Federal fair housing law applies to ADU rentals, though an exemption exists for owner-occupied dwellings with four or fewer units that allows some flexibility in tenant selection. That exemption does not apply to advertising; you cannot make discriminatory statements in rental listings regardless of how many units you own. No exemption under any law protects racial discrimination in housing.

When Your Lot Doesn’t Fit the Rules

If your property can’t meet the standard zoning requirements, say your lot is too small for the required setbacks or the only workable location sits closer to a property line than the code allows, you can apply for a variance from your local board of zoning appeals. Ohio courts evaluate area variances using a seven-factor test known as the Duncan Factors, which weigh your practical difficulties against the impact on surrounding properties. A variance isn’t a rubber stamp. You’ll need to show that strict compliance creates a genuine hardship specific to your property, not a general preference to build something the code doesn’t allow.

1
Ohio Legislative Service Commission. Ohio Constitution Article XVIII Section 3 – Municipal Powers
2
Ohio Legislative Service Commission. Ohio Revised Code Chapter 713 – Planning Commissions
3
Ohio Legislative Service Commission. Ohio Revised Code Chapter 519 – Township Zoning
4
City of Cincinnati. Accessory Dwelling Units
5
City of Columbus. Housing For All
6
Westerville Code of Ordinances. Westerville Code 1175.06 – Residential Accessory Structures
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City of Lakewood, Ohio. How to Apply for an ADU
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City of Cincinnati. Permit Review Process
9
Franklin County Auditor. Rental Registration