ADU rules in Lexington County

The Lexington County Zoning Ordinance has no accessory dwelling unit use; a second detached home is simply another principal dwelling (a site-built Residential Detached unit, a Tiny Home of about 400 square feet or less, or a Mobile Home), and the ordinance regulates how many homes a parcel may hold through density rather than a one-house-per-lot rule. Residential Detached is listed in every district, and Section 22.30 caps density at 2 dwelling units per acre in R1, D and RA, 3 in R2 and 4 in R3 (4 is also the countywide ceiling), with the street classification cap applying when it is lower (1 per acre on Residential Local One and Two streets). In practice a second house needs roughly 1 acre in R1, D or RA, two-thirds of an acre in R2, half an acre in R3 or the commercial districts, and 2 acres on an RL1 or RL2 street, which rules out most suburban lots. Secondary units are barred outright in Residential Detached (Limited) patio-home developments, and a pre-existing undersized lot may support only one dwelling.

There is no attached or internal accessory unit use. A second unit inside or attached to a house makes the building a Residential Attached - Duplex (two dwelling units in one structure separated by a common wall), which Section 21.31 allows only in R3, RD, C1, C2, ID and LR, not in the R1, R2, D or RA districts that cover most single-family land. Duplexes also need a street classification that allows them (Arterial, Collector, Local, RL6, RL5 or Boulevard, not RL4, RL2 or RL1) and must meet the same Section 22.30 density as detached homes. The ordinance's definition of attached also sweeps in units joined to the house by a covered walkway.

Because the county treats a second home as a full principal dwelling, there is no square footage cap relative to the main house. The Tiny Home use is defined as units generally 400 square feet or less excluding lofts, and a Mobile Home must be a HUD-code manufactured home. Any second dwelling must meet the Residential Detached buffering restrictions in Section 23.60 (10 feet from adjoining property lines, 20 or 30 feet from the road right-of-way) and the density limits of Section 22.30.

Nothing in the ordinance requires the owner to live on a parcel with two dwellings. Owner residence matters only for a third manufactured or tiny home: three mobile and/or tiny homes within 1,000 feet of one another count as a Mobile Home or Tiny Home Park (a Board of Zoning Appeals special exception) unless the property owner lives in one of the three as a legal residence. The county's Zoning FAQ states the same rule (two mobile homes, or three if the owner resides in one).

Section 22.20 sets minimum off-street parking per dwelling unit by activity: Residential Detached 3 per dwelling unit, Residential Detached (Limited) 2, Residential Attached 2, Mobile Homes 2 per unit and Tiny Home 2 per dwelling unit. A second dwelling therefore adds its own full requirement; there is no reduced ADU ratio.

Where the parcel's district, street classification and density allow the additional dwelling, approval is a staff-issued zoning permit from the Zoning Administrator under Section 171.10, followed by a building permit; the chart marks only asterisked uses (such as Mobile Home or Tiny Home Parks) as Board of Zoning Appeals special exceptions. Anything beyond the density limit would need a rezoning or variance rather than a routine permit. In the Limited Restriction (LR) district, which covers the county's lightly regulated areas, residential activities are permitted without review for compliance with the ordinance's specific provisions.

The ordinance's definition of dwelling expressly includes units rented or leased, and nothing limits long-term rental of a second home. Since January 1, 2025, Article 13 requires an annual Short-Term Rental Zoning Permit for every short-term rental (1 to 29 consecutive days), owner-occupied or not, with no grandfathering; the % rows of Section 21.31 allow STRs wherever the residential use itself is allowed. Operating rules include a two-night minimum stay, a booking guest at least 25 years old, maximum overnight occupancy of two persons per bedroom, the permit number in every listing, a local contact who can be on site within 45 minutes, neighbor notification, a septic Good Operating Condition report, and 1 parking space per bedroom; two violations within 365 days revoke the permit, with reinstatement only through the Board of Zoning Appeals. The county does not issue business licenses, so the zoning permit is the county-level license.