ADU rules in Louisville

A detached ADU (a converted garage or new accessory building) is a permitted use with special standards in the single-family districts R-R, R-E, R-1, R-2, R-3, R-4, R-5 and U-N, approved by Office of Planning staff when it meets every standard of LDC 4.3.27: one ADU per single-family lot, located to the side of or behind the house, meeting accessory-structure setbacks, with its entrance facing the house or side yard. A detached ADU that cannot meet a standard can still be sought through a conditional use permit from the Board of Zoning Adjustment under LDC 4.2.3. New habitable floor area may not be built on environmentally constrained parts of a lot.

An attached ADU (converted living space, an attached garage, a basement or attic, or an addition) is allowed on the same terms as a detached one in R-R, R-E, R-1 through R-5 and U-N, with one ADU of either type per single-family lot. It must meet the principal structure's setbacks, sit to the side of or behind the house, and any exterior staircase to an upper-story ADU may not be on the front facade. Relief from these standards requires a conditional use permit under LDC 4.2.3.

LDC 4.3.27.B caps an ADU at 800 square feet or 30 percent of the gross floor area of the principal structure, whichever is greater, so a 3,000 sq ft house can carry a 900 sq ft ADU. An attached ADU may not exceed the height of the principal structure; a detached ADU may not exceed the accessory-structure height limit of the form district (LDC Chapter 5) and may not be taller than the house. Larger or taller units need a conditional use permit with written justification under LDC 4.2.3.

LDC 4.3.27.J requires that the owner of the property reside in either the principal dwelling or the ADU; the standard is written as a continuing condition of the use, not only an application test. The Office of Planning's ADU page states that if the owner does not live on the property a permit may not be issued through the pre-approved plan process and that the permit description must indicate ownership. A conditional use permit under LDC 4.2.3 can in principle request relief from a 4.3.27 standard, but the Board of Zoning Adjustment decides case by case. Kentucky has no state ADU statute, so no preemption applies.

LDC 4.3.27.H says only that off-street parking shall meet Chapter 9. Table 9.1.3B has no ADU row: its single-family and duplex row sets no minimum in the Traditional form districts (Traditional Neighborhood, Marketplace Corridor, Workplace), and Table 9.1.3A makes minimums inapplicable Downtown and in Urban Center Neighborhood, while Suburban form districts carry a minimum of 2 spaces per unit, with garages and carports counting. The LDC does not say whether an ADU counts as a unit for that minimum (the ADU definition excludes it only from density calculations), and the nonconforming-parking rule in 9.1.3.B.1 exempts structures at least 50 years old from the minimums. Confirm the count with the Office of Planning for a suburban lot.

Uses in LDC Chapter 4 Part 3 are processed under the Category 2 review procedure (LDC 11.6.3), in which the Planning Director approves the plan if it complies with the code, followed by a building permit; applications now go through the Louisville Metro Business Portal. Ordinance No. 92, Series 2021 (LDC Reform, effective on passage, approved 7-8-2021) created this administrative route; before it, accessory apartments needed a conditional use permit. Waivers and variances of 4.3 special standards are not allowed (LDC 4.3.1), so any deviation goes to a Board of Zoning Adjustment conditional use permit hearing under LDC 4.2.3. Sites with zoning, property maintenance or building code violations in the prior 12 months need sign-off from the directors of planning and codes, and properties in local preservation districts need a certificate of appropriateness.

LDC 4.3.27.F states that ADUs approved under that section shall not be used as a short term rental (a tenancy under 30 consecutive days), so the ordinary staff-approved ADU may be rented only for 30 days or more, with the owner living in the house or the ADU. The Office of Planning reads this as no short-term rentals without a conditional use permit; the route is an ADU conditional use permit under LDC 4.2.3 seeking relief, layered on the short-term rental rules of LDC 4.2.63 and 4.3.23 (owner primary residence for six months before applying, 600 ft spacing between conditional-use rentals, occupancy caps). Every short-term rental must also be registered annually under Metro Code §115.516 (Chapter 115 as amended by Ord. 130-2023). The LDC contains no clause on separate sale of an ADU.