ADU Guide · Verified 2026
Building an ADU in Ohio
Ohio has no statewide ADU mandate. Each city and county sets its own rules, and Columbus is generally the most permissive major city in the state.
Quick Facts
Statewide floors set by No statewide ADU law; local zoning controls. Your city may be more generous but cannot go below them.
The Three Types of ADU
No state floor to rely on
Ohio has never passed a statewide ADU law of any kind. Every rule, whether an ADU is allowed at all, its maximum size, its setback and parking requirements, comes from the specific city or county where the property sits.
Columbus leads the state, locally
Columbus is the Ohio city most commonly cited as ADU-permissive, but that permissiveness comes entirely from its own local zoning code, not any statewide requirement, and doesn't extend automatically to neighboring cities or counties.
What people get wrong
The most common mistake is assuming a rule that works in Columbus applies broadly across Ohio. With no state floor, the local zoning office is the only reliable source for any specific Ohio property.
From Idea to Move-In: The Timeline
Who Administers It
Counties With Their Own Rules
These Ohio counties have verified, county-specific ADU rules that add to the state baseline:
Building It Yourself? Here's What You'll Need
Planning an ADU? Tools homeowners use in the design and layout phase:
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Check Your Local Rules
Your city may allow more than the state floor
State law sets the minimum; many Ohio cities and counties are more generous. Browse the full directory of 88 counties and every city in Ohio for local rules, fees, and building department contact details.
Browse the full Ohio directory →Not sure if your project needs a building permit, a zoning approval, or both? See our guide to building permits vs. zoning approval.
Official Sources
ADU law changes frequently and local ordinances add detail. This guide is general information, not legal advice, always confirm with your local building department. Reviewed by the StateDataIndex Editorial Team · Updated September 2026.