What's Required in Cincinnati
- Lot with single-family use and a single-family house; one ADU per lot; separate exterior entrance.
- Detached ADU: 25 ft maximum height; footprint 15% of lot or 800 sq ft (lots of 4,000 sq ft or more); accessory-structure setbacks; not in the front yard.
- ADU floor area no larger than the finished area of the main house; no more than two accessory buildings on the lot.
- Owner or responsible person must reside on the property; covenant recorded with Hamilton County; registration through ezTrak renewed every odd year.
- Sewer and water availability requests to MSD and GCWW, and a new address from DOTE, before applying for permits.
- Building permit with full plans (site plan, floor plans, elevations, sections, structural), $49 processing fee at application.
- Separate HVAC, plumbing and IBI electrical permits; OCILB-licensed trade contractors registered with the city.
- State-required inspections from soil through finals; certificate of occupancy ($65) after the covenant is recorded.
Can you build an ADU in Cincinnati?
Yes, since October 2, 2023, on any lot that allows single-family use and contains a single-family house. Zoning Code 1421-06 allows one accessory dwelling unit per lot, inside the house, as an addition, or detached, and lots with duplexes, triplexes or apartment buildings cannot add one. The unit must have its own exterior entrance. A detached ADU may not exceed 25 feet in height, measured to the midpoint of the highest gable, and its footprint on a lot of 4,000 square feet or more is capped at 15% of the lot or 800 square feet, whichever is greater; on a smaller lot the house and ADU together may cover 60% of the lot or 800 square feet. The ADU may not be larger than the finished floor area of the main house, counts toward the two-accessory-building limit, must be permanent construction with permanent utilities (no tiny homes on wheels or RVs), and is exempt from off-street parking. Converting an existing garage is allowed even if it breaks the coverage or setback rules, as long as the footprint does not grow.
The condition that matters most: the owner, or a designated responsible person, must live in either the house or the ADU for as long as the ADU exists. You record a covenant approved by the City Solicitor, register the ADU with the Zoning Administrator through ezTrak, and renew the registration by December 31 of every odd-numbered year. Breaking the occupancy rule is a Class F civil offense with a $15,000 fine. The city will not issue the certificate of occupancy until the covenant is recorded.
How much does a Cincinnati ADU permit cost?
The building permit is priced by the value of the building work on the schedule effective July 1, 2026: $1,065 at $50,000 and, above that, $1,065 + $11.59 for every $1,000 of valuation, plus the $49 processing fee and five surcharges (3% technology, 1% training, 1% financial recovery, 5% planning, 1% state), about $11 per $100. Then the trades. A new HVAC installation is valuation based too, $369 at $8,000 plus $49 processing. New plumbing fixtures are $97 for the first, $130 for two, $229 for five. The Inspection Bureau, Inc. (IBI), which issues every electrical permit in the city, charges $60 processing plus $85 for a new single-family unit or multi-room addition, pre-calculated at $146.45. The residential certificate of occupancy is $65.
Worked examples: a $60,000 garage conversion is $1,065 + $11.59 x 60 = $1,760.40, plus $49, about $2,008 with surcharges; add HVAC ($369 + $49, about $464), five plumbing fixtures ($229, about $254), IBI $146.45 and the $65 certificate: roughly $2,937. A $150,000 new detached ADU is $1,065 + $11.59 x 150 = $2,803.50, plus $49, about $3,166 with surcharges; with the same trades the total is roughly $4,095. Zoning registration, the covenant and the new address are separate steps.
| What you are doing | City filing | Rule |
|---|---|---|
| Basement or attic apartment with its own exterior door, $40,000 of work | Building permit about $1,053 + trades | $900 + $49 + surcharges; setbacks do not apply inside the existing house |
| Garage conversion, $60,000 of work | Building permit about $2,008 + trades | $1,065 + $11.59 x 60 + $49 + surcharges; footprint may stay as is |
| New detached ADU, $150,000 of work | Building permit about $3,166 + trades | $1,065 + $11.59 x 150 + $49 + surcharges; 25 ft height cap |
| New heating and cooling system, $8,000 | HVAC permit about $464 | $369 + $49 processing + surcharges; new RCO installation column |
| Kitchen sink, lavatory, toilet, shower, water heater | Plumbing permit about $254 | 5 new fixtures $229 + surcharges |
| Electrical for the new unit | IBI permit $146.45 | $60 processing + $85 new single-family or multi-room addition |
| Certificate of occupancy | $65 | Issued only after the owner-occupancy covenant is recorded |
Steps before the building permit
The city's ADU flowchart front-loads the checks: call the Zoning Division at 513-352-2430 for your district's rules, submit the free sewer and water availability requests to MSD and Greater Cincinnati Water Works, and email a site plan to the transportation department for a new address, which must exist before you apply for permits. Plans for a one- to three-family property need no architect's seal but must show the site plan, floor plans, elevations, sections and structural details. Residential plan review targets 10 working days, revisions 5.
Who builds it
An owner-occupant of a one- to three-family home may act as their own builder if they will live there a year; hired contractors need the $131.25 city registration, and electrical, plumbing and HVAC work must be by OCILB-licensed contractors registered with the city. Inspections run from soil and foundation through rough trades, framing and insulation to finals from plumbing, IBI and mechanical, then the certificate of occupancy.
How to Get a ADU Permit in Cincinnati
Check zoning and utilities
Call the Zoning Division, submit the free MSD sewer and GCWW water availability requests, and request an address from DOTE.
Design the unit
Prepare site plan, floor plans, elevations, sections and structural details that meet the 1421-06 size, height and setback limits and the Residential Code of Ohio.
Register and draft the covenant
Sign the ADU Owner Acknowledgement, register the ADU in ezTrak and email the draft occupancy covenant to zoninginfo@cincinnati-oh.gov for review.
Apply for permits
File the building permit with the $49 processing fee at the Permit Center, then HVAC and plumbing with the department and electrical with IBI.
Build, inspect, record, occupy
Pass soil, foundation, rough trade, framing, insulation and final inspections; record the covenant with the County Recorder and receive the $65 certificate of occupancy.