In plain words

South Carolina has no statewide ADU law. An ADU, or accessory dwelling unit, is a small second home on the same lot as a house. It might be a backyard cottage, a garage apartment, or a suite inside the house. Because the state has not set rules, each city, town and county decides through its zoning. Zoning is the local rulebook for what can be built where. Some places allow ADUs widely. Others allow them only in certain zones, or not at all. Rules can even differ between a city and the county land around it. Owner occupancy means the owner lives on the property, in the house or in the ADU. Two of the state's biggest cities require it. The City of Charleston can approve an ADU in any zoning district. It caps them at 850 square feet and requires the owner to live on site. It also blocks short-term rentals on lots with an ADU. Columbia allows one ADU next to a single-family home. It caps the size at 1,000 square feet or half the house, whichever is smaller. It requires an owner on site, one extra parking space, and rentals of at least 30 days. A 2007 state law asks local plans to study affordable housing ideas, and it names accessory dwellings as one option. It does not force any town to allow them. A bill offering a property-tax break for affordable ADU rentals has stalled. Before you plan, check your local code and your HOA rules. You may be able to build only if local rules and your property allow it.

The rules at a glance

State ADU lawNo. Each city, town or county decides.
Owner living on siteTowns may require the owner to live on the property.
ParkingState law doesn’t set this. Local rules vary; for example, Columbia requires one extra off-street space for an ADU, and the City of Charleston requires three spaces on a lot with a house and an ADU.
SizeState law doesn’t set this. Local caps vary: 850 sq ft of conditioned space in the City of Charleston; the lesser of 1,000 sq ft or half the main home in Columbia; up to 1,500 sq ft of heated space in rural unincorporated Charleston County.
Lot size and setbacksState law doesn’t set this. Cities and counties set lot size, setback and placement rules in their own zoning codes.
FeesState law doesn’t set this. Permit and impact fees are set locally.
Short-term rentalsState law doesn’t set this. Local rules vary; the City of Charleston does not issue short-term rental permits for lots with an ADU, and Columbia bars renting an ADU for less than 30 days.

What to do next

  1. Find out whether your property is inside city or town limits or in unincorporated county land; your county GIS map shows this, and it decides whose zoning code applies.
  2. Look up your zoning district and read the ADU or accessory-dwelling section of that local code, or call the planning and zoning office and ask.
  3. Ask specifically about owner-occupancy rules, size caps, parking, and whether short-term rentals are allowed, since these vary the most across South Carolina.
  4. Read your deed and any HOA covenants; private restrictions can ban a second unit even where zoning allows one.
  5. If the property uses a septic system, check with the state septic permitting office early, because a second unit may need a larger or new system.
  6. Get building and zoning permits before construction, and expect a recorded covenant or affidavit where owner occupancy is required.

What your town still decides

There is no state rule that makes cities or counties allow ADUs. Local governments zone under the South Carolina Local Government Comprehensive Planning Enabling Act of 1994 (S.C. Code Title 6, Chapter 29), and each one decides whether ADUs are allowed, in which zones, at what size, whether the owner must live on site, and how much parking is needed. Rules differ between a city and the county around it, so the first question is whether a property sits inside city limits or in unincorporated county land. Since 2007 the Priority Investment Act has asked local plans to study barriers to affordable housing and incentives such as accessory dwellings, but it creates no mandate. Private covenants and HOA rules can also ban ADUs. A 2026 state law (Act 241 of 2026, H.5113) protects replacement of nonconforming manufactured homes and narrows modular-home standards, but it does not address ADUs.

Examples of local rules

  • City of Charleston: Since a September 2020 ordinance, ADUs may be approved as a conditional use in any base zoning district, one per lot, with no more than two homes on the lot in total. The ADU is capped at 850 square feet of conditioned space. The owner must live in either the house or the ADU under a recorded covenant, the lot needs three off-street parking spaces, and lots with an ADU cannot get a short-term rental permit. Source
  • Columbia: UDO Sec. 17-4.3(d)(1) allows one ADU as an accessory to a single-family detached home in residential districts, subject to standards. The owner must live full time in the house or the ADU. Size is limited to 1,000 square feet or half the main home's floor area, whichever is less. Detached units must be 10 feet from the house; manufactured homes and RVs cannot be used. One extra parking space is required, rentals under 30 days are banned, and the ADU must share the house's address, utilities and driveway. Source
  • Charleston County (unincorporated): One ADU per lot, and a zoning permit is required before converting an accessory building into an ADU. In rural areas the ADU can have up to 1,500 square feet of heated space, but the lot must be at least 50% larger than the district's minimum lot size. ADUs must meet district setback and coverage rules, and attached ADUs cannot have a separate electric meter. Source

What we’re still confirming

  • Whether North Charleston adopted the citywide ADU rules it proposed in January 2025 isn't confirmed; check with the city.

Laws, bills and citations

The laws behind this (1)
  • Housing element and 'market-based incentives' in local comprehensive plans (S.C. Code §6-29-510(D)(6) and §6-29-1110(3); 2007 Act No. 31 (Priority Investment Act), signed January 1, 2007, in effect May 23, 2007). Requires each local comprehensive plan to include a housing element that looks at rules adding needless cost to affordable housing and at incentives that could encourage it. The law's definition of those incentives lists design flexibility that promotes infill, mixed use and accessory dwellings as one example. It encourages towns to consider ADUs but does not require anyone to allow them. Read it
Proposed and failed bills (2). None of these is law.
  • H.3469 (2025-2026): in committee as of October 3, 2026. The Accessory Dwelling Unit Affordable Housing Incentive Act would exempt an ADU's value from property tax if the owner earns under 250% of area median income, rents to a tenant earning 80% or less of it, accepts Section 8, follows local zoning, and keeps the unit affordable for 10 years. It has sat in House Ways and Means since January 14, 2025. The regular session ended May 14, 2026, so it is not expected to move before the two-year session closes. Bill page
  • H.5372 (2023-2024): died as of October 3, 2026. An earlier version of the same ADU property-tax break, introduced April 9, 2024. It never left House Ways and Means and died when the session ended. Bill page

Sources

  1. S.C. Code §6-29-510(D)(6) and §6-29-1110(3); 2007 Act No. 31 (Priority Investment Act) · official source
  2. H.3469 (2025-2026) Accessory Dwelling Unit Affordable Housing Incentive Act, bill page · official source · checked 2026-10-03
  3. H.5372 (2023-2024) Accessory Dwelling Unit Affordable Housing Incentive Act, bill page · official source · checked 2026-10-03
  4. H.5113 (2025-2026) Manufactured and modular homes, Act 241 of 2026 (no ADU provisions) · official source · checked 2026-10-03
  5. H.4293 / S.530 (2025-2026) Zoning enforcement bills (no ADU provisions) · official source · checked 2026-10-03
  6. S.883 (2025-2026) Sine die resolution, regular session ended May 14, 2026 · official source · checked 2026-10-03
  7. City of Charleston, Accessory Dwelling Unit (ADU) · official source · checked 2026-10-03
  8. City of Charleston, Backyard Homes (2020 ordinance background) · official source · checked 2026-10-03
  9. Unified Development Ordinance of the City of Columbia (compiled June 30, 2026), Sec. 17-4.3(d)(1) · official source · checked 2026-10-03
  10. Charleston County Zoning & Planning, Code Enforcement (ADU rules) · official source · checked 2026-10-03
  11. Post and Courier, North Charleston looks to allow accessory dwelling units · checked 2026-10-03

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.