Building an ADU in Ohio

Ohio has no statewide ADU law

No Ohio law makes cities, villages, townships or counties allow ADUs. A search of the Ohio Revised Code on the state's official code site finds no section that uses the phrase "accessory dwelling." Your local zoning code decides whether you can add a backyard cottage, garage apartment or basement unit, and on what terms.

Ohio cities and villages zone under their own powers. The Ohio Constitution gives municipalities "authority to exercise all powers of local self-government and to adopt and enforce within their limits such local police, sanitary and other similar regulations, as are not in conflict with general laws." State law also lets a city's planning commission propose zoning districts that regulate "the height, bulk, and location" of buildings, yards and open space, and "the uses of buildings and other structures," and lets the city council adopt them.

Outside city and village limits, township trustees and county commissioners "may regulate by resolution" the "location, height, bulk, number of stories, and size of buildings" and the "uses of buildings" and land in unincorporated areas. So if you live in a township, the township's zoning resolution (or the county's) is usually the place to look. [1][2][9][10][11][12]

ADU bills in the 2025-2026 legislature

A search of the Ohio Legislature's 136th General Assembly (2025-2026) bills for "accessory dwelling" finds four bills: HB 96, SB 145, HB 313 and HB 585. None of them would require local governments to allow ADUs, and as of October 10, 2026, only HB 96 (the state budget) had become law, without an ADU provision.

• SB 145 (Sens. Reynolds and Craig) would rename the Department of Development the "Department of Housing and Development." It would require the department to publish an "Ohio housing toolkit" with "information and guidance specific to alternative forms of housing such as accessory dwelling units," and a list of local governments that allow them. It was referred to the Senate Housing Committee on March 19, 2025, with no later action.
• HB 313 (Reps. Mathews and Isaacsohn) would create a grant program for townships and municipalities that adopt at least three pro-housing policies, with $50 million a year for fiscal years 2026 and 2027. "Allow accessory dwelling units" is one of the listed policies. It was referred to the House Development Committee on June 4, 2025, with no later action.
• HB 585 (Reps. Odioso and Lett) concerns state money that helps county boards of developmental disabilities buy or build housing for people in supported living. The House-passed version says that money may be used for "accessory dwelling units," among other housing types. It passed the House on June 10, 2026 and was referred to the Senate Finance Committee on September 30, 2026.

SB 145, HB 313 and HB 585 are proposals, not law. Check the bill pages linked above for later action. [3][4][5][6][9][13][14][15][16]

State housing grants: what passed in the 2025 budget

The House version of the 2025 budget bill (HB 96) included a pro-housing grant program similar to HB 313, with "Allow accessory dwelling units" on its list of policies. The law that took effect is different. Ohio Revised Code 122.636, enacted by HB 96 effective September 30, 2025 and amended by HB 434, offers Department of Development grants to counties, townships and municipalities within 20 miles of a "major economic development project" (at least 700 new jobs or $700 million in private investment) that adopt pro-housing development policies and approve a "major workforce housing project" of at least 100 units.

The policies it lists include faster permit review, lower impact and plan review fees, zoning for "higher density, small lot size, and minimum setback requirements," minimal parking requirements and "non-traditional building structures such as modular or manufactured homes." ADUs are not on that list, and the grants go to local governments, not homeowners. [13][17]

Building codes and manufactured homes

Ohio's state residential building code, the Residential Code of Ohio (Ohio Administrative Code 4101:8, the version effective July 1, 2019), applies to "every one-, two-, or three-family dwelling" and "any accessory structure incidental to that dwelling house." It does not need approval for a one-story detached shed, playhouse or similar structure of 200 sq ft or less, though that work must still meet the code. A local government may adopt additional residential rules that do not conflict with the state code. It must notify the Ohio Board of Building Standards of them, anyone may ask the board to decide whether a local rule conflicts, and the board must decide within 60 days of the notice.

Ohio law also says a "permanently sited manufactured home" is "a permitted use in any district or zone in which a political subdivision permits single-family homes." To qualify, the home must be built to the federal HUD manufactured home standards and must be on a permanent foundation and connected to utilities, be at least 22 feet wide and 22 feet long at one point with at least 900 sq ft of living area (not counting garages, porches or attachments), have at least a 3:12 roof pitch, conventional residential siding and a 6-inch eave overhang, have been made after January 1, 1995, and not be in a manufactured home park. The local government can still apply the zoning rules that apply to all single-family homes (except roof-pitch rules), and deed restrictions can still bar manufactured homes. [18][19][20][21]

Examples: Columbus and Cincinnati

Columbus. The city's ADU Handbook says ADUs are allowed in all residential (R), apartment residential (AR) and mixed-use (MU) zoning districts, but not in a Planned Community District or Planned Unit Development. An ADU may be "1,000 square feet or 65% of the net floor area of the principal building, whichever is greater," can't be larger than the main home, and needs no additional parking; the handbook lists a 25-foot height maximum. The rules are in Section 3332.355 of the Columbus zoning code (Ordinance 2526-2025, November 24, 2025). It allows one ADU on a lot with a single-unit home in residential districts, one on a lot with a one- or two-unit home in an R-2F district, and two in an R-4 district (up to five units on the lot). The code also says an ADU must not exceed "the height of the principal dwelling, or 25 feet," so confirm the height limit for your lot with the city. Questions go to Building and Zoning Services at zoninginfo@columbus.gov or (614) 645-7433.

Cincinnati. According to the city's ADU page, ADUs have been legal since October 2, 2023 on lots that allow single-family use and have a single-family home; lots with duplexes or apartment buildings can't add one. Only one ADU is allowed per lot, and it needs its own exterior entrance. Under the zoning code, an ADU can't be larger than the main house, and a detached ADU can be up to 25 feet tall. The owner, or a designated "responsible person," must live in the house or the ADU, and the owner must record a restrictive covenant and register the ADU with the city. No extra parking is required, and short-term rentals are allowed if registered. The rules are in Section 1421-06 of the Zoning Code; the Zoning Division is at (513) 352-2430.

These are summaries of each city's own guidance. Confirm the current rules with the city before you design anything. [7][8][22][23]

What to check with your city, village or township

Because the rules are local, ask your zoning office:

• Whether your zoning district allows an ADU, second unit or two-family home, and the minimum lot size.
• The maximum ADU size, height and setbacks, and whether it can be detached.
• Whether the owner must live on the property.
• How many parking spaces you need.
• Whether you can rent the ADU, including short term.
• Which building department issues permits for your address, and the permit, plan review and utility connection fees.

Check your deed restrictions and any homeowners' association rules too. Our ADU permit process guide, garage conversion guide, ADU cost guide and tiny house guide cover the general steps. [1][2][12][20]

Ohio laws to know

• Ohio Constitution, Article XVIII, Section 3 (home rule)

  Gives municipalities "all powers of local self-government," including local police regulations that do not conflict with general laws. [10]

• Ohio Revised Code 713.06 and 713.07 (municipal zoning)

  Let a city or village divide its land into zoning districts and regulate building height, bulk, location, yards and uses, which is where city ADU rules come from. [1][11]

• Ohio Revised Code 519.02 and 303.02 (township and county zoning)

  Let township trustees and county commissioners regulate the size, location and use of buildings in unincorporated areas. [2][12]

• Ohio Revised Code 3781.184 (manufactured homes)

  Makes a manufactured home built to federal HUD standards that meets the "permanently sited" conditions in section 3781.06 a permitted use in any zone where single-family homes are allowed. [20][21]

• SB 145 (2025), proposed (in committee)

  Would rename the Department of Development and require a state housing toolkit with guidance on ADUs; it has been in the Senate Housing Committee since March 19, 2025. [4][14]

• HB 313 (2025), proposed (in committee)

  Would create grants for townships and municipalities that adopt pro-housing policies, one of which is allowing ADUs; it has been in the House Development Committee since June 4, 2025. [5][15]

Questions people ask