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Butler County, OH Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Butler County, OH, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

County zoning: None (Ohio has no county zoning)
Governing law: Township zoning, ORC Ch. 519
Who decides: Your township or city
Enabling statute: ORC 519.02
Ask: Township zoning inspector

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Ohio under recent ADU streamlining laws. The Butler County, OH rules below cover local size, height, and setback requirements.

Summary

Butler County has no countywide zoning, so accessory dwelling units are governed by whichever township or city you live in. Ohio townships zone the unincorporated area under ORC Chapter 519; check your township's zoning resolution before adding an ADU.

These county ordinances apply to unincorporated areas of Butler County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

the board of township trustees may regulate by resolution, in accordance with a comprehensive plan, the location, height, bulk, number of stories, and size of buildings and other structures... and the uses of land for trade, industry, residence, recreation, or other purposes in the unincorporated territory of the township.

View official code

Full Breakdown

Ohio law gives no county-wide zoning power to Butler County. Under ORC 519.02 the board of township trustees may 'regulate by resolution... the location, height, bulk, number of stories, and size of buildings and other structures... and the uses of land' in the unincorporated township. So whether a second dwelling, in-law suite, or garage apartment is permitted depends on your township's zoning resolution (e.g. West Chester, Liberty, Fairfield Twp) or your city's code (Hamilton, Middletown, Fairfield, Oxford). Contact your township zoning inspector or city zoning office for lot-size, setback, and owner-occupancy requirements before building.

Violations & Fines

Zoning enforcement is by the township zoning inspector or municipal zoning officer under ORC 519.99 / local code; typically a written violation notice, stop-work, and per-day fines until compliance.

Frequently Asked Questions

Does Butler County approve ADUs?

No. The county has no zoning authority over homes. Your township (unincorporated) or city (incorporated) sets ADU rules.

Which law lets townships regulate this?

ORC Chapter 519 gives township trustees zoning power over unincorporated land, including the size and use of buildings.

Sources & Official References

Other rules in Butler County

Parking Rules: Street Parking LimitsSome Restrictions Noise Ordinances: Quiet HoursSome Restrictions Noise Ordinances: Vehicle NoiseSome Restrictions Parking Rules: Driveway RulesSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Fence Regulations: Material RestrictionsSome Restrictions

All Butler County rules

How Butler County compares: Easiest Cities to Build an ADU·Compare Butler County to another location·View the Ohio accessory structures overview

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