What's Required in Louisville
- One ADU per single-family lot in R-R, R-E, R-1 through R-5 and U-N districts (LDC 4.3.27).
- Maximum size is 800 sq ft or 30% of the house's gross floor area, whichever is greater.
- The owner must live in the house or the ADU.
- The ADU must sit beside or behind the house and meet the applicable setbacks.
- A detached ADU may not be taller than the house.
- No short-term rental under the by-right standards.
- File the Office of Planning ADU application ($50) before the building permit.
- Plumbing needs a state permit; building, electrical and HVAC permits come from Construction Review.
- Deed restrictions or HOA declarations that ban ADUs still apply.
Can You Build an ADU in Louisville?
Yes, in most single-family zones. Land Development Code Section 4.3.27 permits accessory dwelling units in the R-R, R-E, R-1, R-2, R-3, R-4, R-5 and U-N districts, attached or detached, if they meet its special standards:
- One ADU per single-family dwelling per lot.
- Size: up to 800 square feet or 30 percent of the gross floor area of the house, whichever is greater.
- Location: beside or behind the house. An attached ADU meets the house's setbacks; a detached one meets accessory-structure setbacks.
- Height: an attached ADU no taller than the house; a detached ADU no taller than the accessory-structure limit and never taller than the house.
- Owner occupancy: the owner must live in either the house or the ADU.
- No short-term rental under these standards.
- Off-street parking per LDC Chapter 9, and no new habitable floor area on environmentally constrained parts of the lot.
A property with a zoning, property maintenance or building code violation in the prior 12 months needs sign-off from the Planning and Codes and Regulations directors. The section does not override deed restrictions or HOA declarations that ban ADUs. If you cannot meet a standard, you can apply to the Board of Zoning Adjustment for a conditional use permit (CUP). In August 2026, for example, staff recommended a CUP for a 1,024 square foot ADU on a lot owned by an LLC.
Louisville ADU Permit Rules by Scenario
| What you are doing | City filing | Rule |
|---|---|---|
| ADU meeting every LDC 4.3.27 standard | Office of Planning ADU application ($50), then building permit | LDC 4.3.27; Planning fee schedule |
| ADU over 800 sq ft and over 30% of the house | Conditional use permit, $550 | LDC 4.2.3; Planning fee schedule |
| Owner will not live on the property | Conditional use permit, Board's discretion | LDC 4.3.27.J; 26-CUP-0099 |
| Renting the ADU short term | Not allowed under 4.3.27 | LDC 4.3.27.F |
| A second ADU on the lot | Not allowed | LDC 4.3.27.A |
| New plumbing in the ADU | State plumbing permit, $50 + $14 per opening | 815 KAR 20:050 |
| HOA or deed bans ADUs | City approval does not override it | LDC 4.3.27.K |
How Much Does an ADU Permit Cost in Louisville?
There is no single ADU fee; you pay each office. The Office of Planning's ADU application is $50. Construction Review prices new floor area at $.105 per square foot for one- and two-family residential and alterations at $50 plus $2.50 per $1,000, $75 minimum. Electrical wiring of a new one- or two-family residence is $200 with three inspections; other wiring work over $750 is $100. HVAC is $105 for the first system. Plumbing is a state permit at $50 plus $14 per opening.
Worked example, new 800 sq ft detached ADU with six plumbing openings: planning $50; building 800 x $.105 = $84; electrical $200; HVAC $105; plumbing $50 + 6 x $14 = $134. Total: $573. If it needs a CUP, add $550 for $1,123. Garage conversion valued at $30,000: planning $50; building $50 + 30 x $2.50 = $125; electrical $100; HVAC $105; plumbing $134. Total: $514. Sewer and water connection charges are separate and not covered here.
How to Get a ADU Permit in Louisville
Check zoning and deed
Confirm your zoning district on the LOJIC Land Development Report and read deed and HOA restrictions.
Apply to the Office of Planning
Submit the ADU application, letter of explanation and dimensioned site plan with the $50 fee.
Seek a CUP if needed
If you miss a standard, apply to the Board of Zoning Adjustment for a conditional use permit ($550).
Get the building and trade permits
File the building, electrical and HVAC permits with Construction Review and the plumbing permit with the state.
Build and pass inspections
Schedule Metro building, electrical and HVAC inspections and state plumbing inspections.