South Carolina ADU housing laws and regulations: your local zoning rules explained

South Carolina has no state ADU statute, so whether you can add a garage apartment or backyard cottage depends on the county or city zoning ordinance that covers the parcel. Charleston, Columbia, and Greenville do not follow one uniform rule.

Those ordinances disagree on size caps and owner occupancy. They also differ on parking and whether the unit can ever be listed on Airbnb, and your property-tax bill changes the day a tenant moves in. This guide covers the local rules in eight jurisdictions, the septic and permit sequence with real fee figures, what happens to your 4% assessment ratio, and how renting affects your insurance.

South Carolina ADU laws: the short answer

There is no South Carolina statute that requires a city or county to allow accessory dwelling units, and none that preempts local ADU zoning. As of September 28, 2026, every ADU rule in the state comes from a county or municipal ordinance adopted under the Local Government Comprehensive Planning Enabling Act, SC Code Title 6, Chapter 29. If you searched "South Carolina ADU laws" expecting one state rule on size or owner occupancy, that rule does not exist.

The General Assembly has taken up ADUs twice, both times through the property-tax code rather than zoning. H. 5372, filed in 2024, would have amended § 12-37-220 to exempt certain ADUs from property tax; it was referred to House Ways and Means on April 9, 2024 and died at sine die. H. 3469, introduced January 14, 2025 by Reps. Jones and Cobb-Hunter, offered the same exemption for ADUs kept as affordable housing for at least ten years with Section 8 payments accepted as rent. The Municipal Association report records the session closing May 14, 2026 without it passing.

Neither bill touched local authority. H. 5372 required qualifying owners to "comply with all local zoning ordinances and regulations," and H. 3469 carried the same condition. The South Carolina Association of Counties' 2025 policy positions oppose "legislative preemption of local zoning or other restrictions on local land use regulation" and call counties and municipalities "the only entities vested with the jurisdiction to adopt and enforce zoning ordinances, development regulations, and other land use measures."

The activity is all local. The Post and Courier reported that North Charleston took up a citywide ADU ordinance in January 2025. James Island Town Council voted unanimously on November 20, 2025 to adopt ADU definitions and a registration path for existing units.

What counts as an ADU in South Carolina (and what's just a FROG)?

An ADU, or accessory dwelling unit, is a second self-contained home on a lot that already has one. It has its own kitchen and bathroom, plus sleeping space and an entrance, and it is smaller than and subordinate to the main house. The Town of James Island's § 153.013 defines it as "A dwelling unit providing complete independent living facilities for one or more persons that is separate from and subordinate to the principal dwelling unit, while both units are serviced by one electrical meter," and adds that "This definition includes garage apartments."

Attached and detached units are both ADUs, and ordinances treat them differently. Charleston measures its cap in conditioned floor area. Mount Pleasant sets one limit for attached and interior units and a district-by-district limit for detached ones. Columbia's accessory use table requires a detached unit to stand at least 10 feet from the principal structure.

A FROG, the finished room over the garage that appears in Lowcountry listings, is a bonus room unless it has a kitchen. A bedroom and bath over the garage with no cooking facilities does not meet the "complete independent living facilities" test, so it remains part of the principal dwelling and none of the ADU conditions attach to it.

Add a kitchen and a separate lockable entrance, and the same square footage becomes a dwelling unit subject to the size cap and extra parking space. Owner-occupancy covenants and any STR ban may also apply.

Greenville County drew the line at the kitchen for years. Its former zoning ordinance did not allow detached accessory structures with kitchens at all before the December 2024 rewrite. An in-law suite inside the house that shares the family kitchen is part of the house; a suite with its own kitchen and door is an attached ADU, whatever the listing calls it.

Who writes the rules: state enabling act, counties, municipalities

County councils and city councils write South Carolina's zoning under authority delegated by Chapter 29 of Title 6. §§ 6-29-710 and 6-29-720(B) let a governing body adopt a zoning ordinance only after its planning commission has prepared, and the council has adopted, at least the land-use element of a local plan. Every zoning regulation must follow that plan.

The state supplies the framework. The zoning map and use table are local. So are the ADU conditions.

Chapter 29 also supplies the tools cities use for ADUs. § 6-29-720(C) lists conditional uses and overlay zones among the permitted zoning techniques, along with planned development districts. Charleston permits ADUs as a conditional use in every base district, and unincorporated Charleston County writes its ADU rule into the Sol Legare overlay.

Since 2023 Act No. 57, the housing element of every local plan must analyze nonessential housing regulatory requirements that could be eliminated to encourage private development. ADU allowances tend to surface when a council updates that plan.

The planning commission drafts the ordinance and cannot grant variances or make final zoning decisions under § 6-29-320. The board of zoning appeals hears variance requests and appeals from staff decisions. However, § 6-29-780(B) bars it from granting a variance that would allow a use the district does not otherwise permit.

If your district's use table has no ADU line, the BZA cannot create one. You need a text amendment from council.

Confirm which jurisdiction your parcel sits in before you read any ordinance. James Island has three regulators. The Town of James Island has no operative standards for new ADUs. City of Charleston portions of the island allow them as a conditional use under the city ordinance. The unincorporated Charleston County portion follows the Sol Legare overlay with its own smaller cap. Three sets of rules apply on one island.

ADU rules by South Carolina city and county

Charleston, Columbia, Greenville, and Mount Pleasant publish full ADU standards. Greenville County and Rock Hill do not, at least not in code text that could be confirmed as of September 2026. The same gap applies to Horry County, and James Island has definitions but no standards for new construction. The table reflects each jurisdiction's current ordinance text, with gaps flagged where the official code did not settle the question:

• Jurisdiction | Permitted districts | Max size | Owner occupancy | ADU parking | Short-term rental
• City of Charleston | All base districts, as a conditional use | 850 sq ft conditioned floor area | Required, either unit | 1 additional space; tandem allowed | Prohibited; lots with an ADU cannot get an STR permit
• City of Columbia | T/C, LL-R, RSF-1, RSF-2, RSF-3, RD, RD-MV, RM-1, RM-2, MU-1, MU-2 | Lesser of 1,000 sq ft or 50% of principal dwelling | Required, either unit | At least 1 additional space | Prohibited; no tenancy under 30 days
• City of Greenville | Single-family residential zones | 1,000 sq ft | Required, either unit | Not confirmed in retrieved code text | Not confirmed in retrieved code text
• Greenville County (unincorporated) | Not confirmed under the December 2024 UDO | Not confirmed | Not confirmed | Not confirmed | No ADU-specific rule; owner-on-site STR proposal withdrawn September 2025
• Town of Mount Pleasant | RC-1, RC-2, RR, CC, CL, R-1 through R-4, WG-W, and nine named PD neighborhoods | 850 sq ft attached; detached 600–850 sq ft by district, no cap in RC-1, RC-2, RR | Required, either unit | 1 private space; tandem only if it serves the ADU alone | Permitted with Town STR permit and business license; 2026 renewals closed, waitlist only
• Town of James Island | No operative framework for new ADUs | Not established | Full-time owner residence for registered pre-2012 units | Not established | Not yet regulated
• City of Rock Hill | Not confirmed in retrieved code text | Not confirmed | Not confirmed | Not confirmed | Not confirmed
• Horry County (unincorporated) | Not confirmed; an ADU application process exists | Not confirmed | Not confirmed | Not confirmed (2 spaces per single-family unit generally) | No dedicated STR zoning program found; business license and 3% hospitality fee apply

The code sections behind each row, and the details the table leaves out:

• Charleston's § 54-214, current through Ordinance No. 2024-162 (January 21, 2025), allows one ADU per lot with total dwelling units capped at two. It requires a Declaration of Covenants and Restrictions that the city approves, the owner executes, and the owner records prior to completion of construction of the ADU. The city's ADU page confirms detached units are allowed.
• Columbia's rules sit in § 17-4.3(d)(1) of the Unified Development Ordinance, revised June 2026. The unit must be accessory to a single-family detached dwelling, and the owner's residence must be a "permanent, full-time" one in either unit.
• Greenville's Chapter 19 Development Code took effect July 15, 2023. GVL Homes 4 All explains that it permits carriage houses and garage apartments as detached units. The Greenville Journal reported the 1,000 sq ft cap and owner-occupancy condition. Parking and STR treatment were not established by the retrieved official text, so ask the city planning department before you design.
• Greenville County adopted a Unified Development Ordinance on December 3, 2024 that, in the county's words, allows "diverse housing types such as accessory dwelling units and compact homes." Its status is unsettled. The county's own February 2025 planning report records that "On January 14, 2025, the UDO was reconsidered by County Council and sent to the Council's Committee of the Whole for further review and potential amendments." Treat any countywide ADU allowance as pending and call Planning before you design to it.
• Mount Pleasant's § 156.445, effective May 1, 2025, caps ADU occupancy at three persons and requires certificates of occupancy on both units before an STR permit. The nine PD neighborhoods on the Town's ADU requirements sheet are Carolina Park, Cassina Plantation, Central Mount Pleasant, I'On, Pepper Tract, Pinckney Place, Seaside Farms, Wando Farms, and Watermark.
• James Island's Ordinance #2025-10 (November 20, 2025) added definitions and a registration path for pre-existing units only. The Post and Courier reported that size limits and districts had not been written for new construction as of that vote. Parking and STR rules also remained unwritten.
• Rock Hill's code runs through Ordinance No. 2026-26 (June 8, 2026), and Chapter 5 covers "Land Use: Temporary and Accessory Uses," but the retrieved text did not establish ADU standards. Start with the Planning and Development Department.
• Horry County's Planning and Zoning forms page lists an "Accessory Dwelling Unit Notarized Authorization Letter," so an application track exists. Several 2025–2026 ordinances remained uncodified as of April 2026, which is why the standards themselves could not be confirmed.

Size, setbacks, height, and parking limits

Where a South Carolina ordinance sets a hard ADU cap, the published local caps reviewed here fall between 600 and 1,000 square feet. The exact number depends on whether the unit is attached and which district the lot occupies. Unincorporated Charleston County's Sol Legare overlay sets 800 sq ft, with a BZA special exception available up to 1,500 sq ft.

Columbia's percentage cap excludes carports and garages when measuring the principal dwelling. It also excludes unfinished basements, so a 1,600 sq ft house with a two-car garage supports an 800 sq ft unit, not more.

Charleston trades size for setback relief. A detached unit built under the § 54-506(f) setback exceptions is limited to a 600 sq ft building footprint instead of the standard conditioned-area cap. Mount Pleasant runs the other direction in its rural and conservation districts: § 156.424 sets no detached cap in RC-1, RC-2, or RR, subject only to the district's building coverage limit.

Height starts to cost you setback distance in Mount Pleasant. The Post and Courier explains that Ordinance 25051, adopted February 10, 2026, requires ADUs in Old Mount Pleasant and surrounding neighborhoods to sit at least 6 feet from the property line. The setback increases to 10 feet once the unit reaches 18 feet tall.

Columbia adds a 10-foot separation between the ADU and the main house. Septic setbacks under state regulation add another layer on unsewered lots, covered in the permit section below.

Parking rules differ on one point: tandem spaces. Charleston accepts a tandem space of at least 9 ft × 18.5 ft for the extra stall. Mount Pleasant prohibits tandem parking unless the stacked space serves the ADU only. Horry County's general standard is two spaces per single-family or duplex unit, with no ADU-specific figure confirmed.

Owner-occupancy and rental limits, including short-term rentals

A permitted ADU can produce rental income on land you already own. Owner occupancy controls whether that income model works in several cities. Charleston, Columbia, Greenville, and Mount Pleasant each require the owner to live in either the main house or the ADU as a primary residence.

James Island's registered nonconforming units require a full-time owner on the property. Owners can prove residence with a 4% legal residence tax bill or driver's license. Voter registration and vehicle registration also qualify.

For a portfolio investor, that closes the obvious play. You cannot add an ADU to a pure rental in these cities and lease both units to tenants. The structure that works is buying the property, living in one unit, and renting the other.

Charleston records a Declaration of Covenants and Restrictions against the lot before construction of the ADU is complete. The condition therefore follows the deed to the next buyer.

Greenville County is the exception among the jurisdictions reviewed. The current UDO text did not confirm an owner-occupancy rule. The September 16, 2025 council minutes record a proposed amendment to Section 8:5.12 that would have allowed rentals shorter than 30 days "only ... if the property owner lives on-site and occupies the property during the short-term rental period." Its sponsor withdrew the motion, and the ordinance passed without it.

Long-term leases are the default use everywhere ADUs are allowed. Short-term rental is where the income model breaks. Charleston's ADU page states "Neither the principal dwelling unit nor the ADU shall be utilized for a short-term rental" and "Lots with an ADU are NOT eligible for a Short-Term Rental permit." In Charleston you choose between an ADU and an STR permit; the city will not issue both.

Columbia reaches the same result through the lease term. Its accessory use table bars ADU tenancies under 30 days, even though the city reopened owner-occupied STRs in residential zones under Ordinance No. 2026-013 on March 3, 2026 after repealing its 2025 moratorium.

Columbia's annual STR permit runs $100 for owner-occupied units and $250 otherwise. The city also charges a $50 application fee and $10 zoning fee, and it collects a 3% Tourism Development Fee on rental income monthly.

Mount Pleasant is the one reviewed jurisdiction that allows an ADU to operate as an STR. You need a Town STR permit and business license. Both units must also have certificates of occupancy. The Town's STR page shows renewal applications closed for 2026, with remaining permits going to a waitlist, so a new ADU owner in Mount Pleasant is buying a spot in line rather than a permit.

Along the Grand Strand, unincorporated Horry County has no dedicated STR zoning program in the retrieved code. Operators need a state sales-tax number and a county business license (NAICS 721; $30 minimum for residents, $60 for nonresidents on the 2024 schedule). They also need a hospitality and accommodations account.

Operators must remit a 3% hospitality fee on transient rentals by the 20th of the following month. Rentals of 90 or more consecutive days are exempt.

Inside Myrtle Beach city limits, the planning department states that "Zoning districts that begin with R do not allow short-term rentals, with the exception of the RMV (Residential Multifamily Visitor) Zone." Operating without proper zoning is a misdemeanor carrying up to $500 or 30 days per occurrence.

Two state STR bills sat unpassed at the close of the 2025–2026 session. H. 3861 would bar local governments from banning STRs in residential dwellings. S. 442 would expressly authorize local bans and registration. Until one passes, the Charleston and Columbia ADU prohibitions stand.

Can your HOA ban an ADU your city allows?

Yes. A recorded covenant that bars second dwellings controls even when the zoning ordinance permits an ADU. In Seabrook Island v. Marchland (2004), the South Carolina Court of Appeals rejected the argument that a zoning ordinance supersedes restrictive covenants.

A 1994 appellate decision reached the same place when the City of Charleston classified a bed-and-breakfast as a permitted home occupation. The master deed prohibited it, and the deed won.

Courts enforce the specific language. In Easterly v. Hall (1971), a covenant limiting lots to "one single family private dwelling house" supported a permanent injunction against a duplex. In Arcadian Shores v. Cromer (2007), the court enforced a declaration that expressly prohibited a "garage apartment." Pierson v. Marsh (2018) enforced a covenant against "more than one residence on a subdivided lot."

The language has to be there. Under Taylor v. Lindsey (1998), courts strictly construe restrictive covenants and resolve doubts in favor of free use of the property. An HOA therefore cannot imply an ADU ban from a covenant that never mentions second dwellings.

Read your declaration for the words "one dwelling" or "single family residence." Also look for "garage apartment" and "guest house" before you spend money on drawings.

Even an express covenant has defenses. Hardy v. Aiken (2006) held that a covenant with a stated 25-year term expired on that date and a general amendment clause could not extend it. Nash v. The Tara Plantation (2010) recognized waiver and estoppel where an association had allowed second dwellings without objection.

Buffington v. T.O.E. Enterprises (2009) requires courts to weigh waiver and estoppel before issuing an injunction. Courts must also consider laches and changed conditions, though the changed-conditions bar is high: "so radical as to practically destroy the essential objects and purposes of the covenants," under Shipyard Property Owners' Association v. Mangiaracina (1992).

State law offers no relief. The SC Homeowners Association Act contains no provision limiting an HOA's power over ADUs, guest houses, or rentals. The reviewed materials identified no South Carolina bill through September 2026 that would void covenant bans on ADUs.

That differs from California's ADU law: Civil Code § 4751 overrides covenants that prohibit ADUs. § 6-29-1145 requires a local planning agency to ask about recorded covenants and withhold a permit when it has actual notice of a conflicting one. However, the statute's definitions exclude building permits and covenants restricting the type of structure, so do not expect the county to catch the conflict for you.

South Carolina property tax consequence of renting an ADU

Renting a detached ADU moves that unit from the 4% legal residence ratio to the 6% ratio and strips it of the school operating millage exemption, while the house you live in keeps both. The governing statute is SC Code § 12-43-220(c), which grants the 4% ratio to owner-occupied residential property. Subsection (e) assesses all other real property at 6% of fair market value.

The statute protects only rentals inside your own residence. It reads: "However, if the person claiming the four percent assessment ratio resides in the mobile home or single family residence and only rents a portion of the mobile home or single family residence to another individual as a residence, the foregoing provision does not apply and the four percent assessment ratio must be applied to the entire mobile home or single family residence." A rented bedroom or a kitchen-less FROG falls under that sentence. A separate dwelling does not.

The SCDOR 2014 legislative update states: "If this property has located on it any rented mobile homes or residences which are rented or any business for profit that the 4% value does not apply to those businesses or rental properties."

Charleston County's legal residence application puts it in plain terms: "If the property has additional dwelling(s) or is a duplex/triplex, only dwellings or units occupied by immediate family members qualify for 4% ratio. If rented, the property will be taxed at partial 4% / 6%."

An ADU occupied by your parent or adult child keeps the 4% ratio. A 2022 unpublished Court of Appeals opinion held the statute does not demand continuous occupation by the family member.

The school millage loss compounds the ratio change. SC Code § 12-37-220(B)(47)(a) exempts 4%-eligible property from all school operating taxes, but not debt-service millage. SCDOR's 2025 policy manual states that "if only a portion of the residential property is eligible for the 4% assessment ratio, only that portion will be subject to the exemption for school operating costs." The rented ADU pays school operating millage in full.

SCDOR publishes no allocation formula. The Administrative Law Court has accepted square footage as the split method for owner-occupied duplexes. You can request a private ruling from SCDOR if your assessor's allocation looks wrong.

• The 72-day rule does not rescue an ADU. Under § 12-43-220(c) and SCDOR Revenue Ruling 15-4, an owner's primary residence rented 72 days or fewer per calendar year keeps its 4% status. That rule governs the residence you live in, not a second dwelling on the lot.
• You also get one legal residence. The Administrative Law Court in Guthrie v. Orangeburg County Assessor (2001) held the term "must be construed in the singular number, and must, therefore, be understood to refer to a single dwelling of the taxpayer."
• Tell the assessor within six months of the first lease. Horry County's assessment guide states the six-month change-of-use deadline, and Charleston County requires notice of rental even below 72 days.
• The penalty for an improper 4% claim, as shown on Dorchester County's audit page, is 100% of the tax paid at the 4% rate plus interest at 0.5% per month. The minimum is $30, and the maximum is the current year's taxes.

Permits, septic and sewer, and what it costs: a worked example

Published fee schedules put permit soft costs for a 700 sq ft detached ADU at roughly $600 in the City of Charleston and roughly $1,500 in Horry County before water and sewer. The worked examples below show that utility connection fees can exceed the permit subtotal. A typical approval sequence follows these steps, with the septic-or-sewer requirement depending on the lot:

1. Verify zoning. Confirm that the district allows an ADU and that the lot meets the size and setback rules. Then check for a recorded covenant that blocks it. York County's ADU permit packet (July 2025) shows the typical checklist.
2. Secure wastewater approval before the building permit. On a sewered lot, request a service availability letter and pay the tap and capacity fees. On septic, obtain a Permit to Construct from the SC Department of Environmental Services (SCDES). York County will not issue a building permit without a "Septic Permit (DHEC), Paid Water & Sewer Tap Fee Receipt, or Septic Verification Letter."
3. Submit the building permit application with plans. Valuation-based fees apply in Charleston and Greenville County; per-square-foot fees apply in Horry County.
4. Pass plan review. Published targets run 3 business days in Columbia and 5 in Greenville County. Horry County publishes 7–10 working days, while Mount Pleasant publishes 4–6 weeks.
5. Pay impact fees where they exist. Charleston and Charleston County charge none. Greenville County also charges none, while Horry County charges a size-based fee.
6. Schedule inspections and the final certificate. Charleston schedules inspections requested before noon for the next business day and issues the Certificate of Construction Completion 3 business days after final inspections.

Septic is where rural and suburban ADUs stall. SCDES took over onsite wastewater permitting from SCDHEC on July 1, 2024 under Regulation 61-56. The regulation prohibits construction on a dwelling served by a septic system until a Permit to Construct issues. It also requires an upgrade permit when a second dwelling or added bedrooms increase wastewater flow.

You apply on Form D-1740 through the ePermitting portal with a plat or deed. Stake the corners and clear underbrush within 150 feet of the proposed system. The site evaluation fee is $150, and the Permit to Construct remains valid for five years.

The blocker is the reserve area. Every site must hold a usable repair area equal to at least 50% of the original system. The system needs 5 feet from any building or property line and 75 feet from a private well. It needs 100 feet from a public well and 75 feet from a tidal critical-area line.

SCDES sizes systems at 120 gallons per bedroom per day, with a 1,000-gallon minimum tank for four bedrooms or fewer and 250 gallons per bedroom above four. An ADU footprint or driveway placed over the repair area kills the permit.

SCDES publishes no fixed processing time. Applications run first come, first served, and wet weather delays soil evaluations. The agency's 2026 dashboard sets a 90-day goal, not a deadline.

Here is what the soft costs look like for a 700 sq ft heated detached ADU in three jurisdictions, using each jurisdiction's published fee schedule:

• Cost item | City of Charleston | Greenville County | Horry County
• Valuation basis | $116.15/sq ft heated = $81,305 | $251.10/sq ft heated = $175,770 | $0.50/sq ft flat
• Building permit fee | ~$385 | ~$1,031 | $350
• Plan review fee | ~$193 (half of permit) | Not stated on residential fee sheet | $140 ($0.20/sq ft)
• Application or zoning fee | $40 | None listed | $25
• Impact fee | $0 | $0 | $995 (1,000 sq ft or less)
• Permit subtotal | ~$618 | ~$1,031 | ~$1,510
• Water and sewer connection | ~$11,990 (Charleston Water System, 3/4" tap, 1 ERU) | ~$7,750 (Greenville Water + ReWa, 5/8" meter, 1-BR) | ~$6,440 (GSWSA, 1 REU)
• Soft-cost total before construction | ~$12,600 | ~$8,780 plus plan review | ~$7,950

Sources: Charleston fee schedule (effective October 1, 2019); Greenville permit fees (effective July 1, 2025, including a 20% increase); Horry County permit costs and Ordinance 30-2026 impact fees effective July 20, 2026, as reported by WPDE; Charleston Water System, Greenville Water, ReWa, and GSWSA fees all effective in 2026.

Horry County's impact fee assumes the ADU is classed as single-family; confirm that with Code Enforcement. Greenville County's heated valuation rate is more than double Charleston's, which is why the same building draws nearly triple the permit fee.

Charleston's $0 impact fee reflects an ordinance that expired December 31, 2015, as the Post and Courier reported. Greenville County Council's planning committee voted in February 2026 to end its road impact fee study.

Construction dwarfs all of it. No methodology-driven statewide survey of South Carolina ADU costs exists, so the figures below are builder-published and should be read as vendor quotes. Burch Contracting lists $125,000–$185,000 all-in for 600–800 sq ft in the Upstate. Chonko Construction lists $203–$379+ per sq ft in Columbia with roughly $188,300 typical for 500–900 sq ft. Baldwin Builders lists $170,000–$250,000+ for site-built coastal units and $130,000–$160,000 all-in for a 400–600 sq ft prefab.

The Post and Courier quoted Brad Sundt of Anchored Tiny Homes in July 2024 at roughly $123,000 for a one-bedroom unit and $165,000 for two bedrooms.

On elapsed time, a Charleston sewered lot moves fastest on paper. Charleston Water System returns a service availability letter in 5–10 business days. The city publishes no fixed plan-review target, but it cut its technical review backlog from 67 cases to 5 after 2024 administrative changes. The final certificate follows 3 business days after inspections.

Columbia Water is the outlier on utilities, estimating 12 weeks for a new main-line tap and 6–8 more if the existing stub-out is concealed. Burch Contracting estimates 10–16 weeks from zoning review through utility connections for an Upstate project. Baldwin Builders estimates 4–8 weeks for a Horry County permit package, with OCRM coastal review adding 30–90 days in jurisdictional areas.

H. 3215, which would impose a 45-day deemed-approval deadline on local permit reviews, was still in House committee at session's end.

Already have an unpermitted ADU? Grandfathering and remediation

James Island's § 153.362 is the only South Carolina amnesty path retrieved, and it is narrow. The ADU must have existed on or before October 18, 2012. You carry the burden of proving it with sworn affidavits from adjacent owners and others with personal knowledge, plus any other evidence the Zoning Administrator requires.

Approval is required "in order to continue occupancy," and the ordinance sets no application deadline. No fee appears in the ordinance; the Town Council sets fees by resolution.

Registration under § 153.362 requires all eight of the following:

• Apply for and receive Zoning Administrator approval to continue occupancy.
• Hold no more than one nonconforming registered ADU on the lot.
• Live on the property full time as the owner, documented by a 4% legal residence tax bill, driver's license, voter registration, or vehicle registration.
• Keep both units on one electrical meter; separate meters are prohibited.
• Comply with FEMA flood plain management regulations and the Town's flood ordinance.
• Leave the existing footprint alone; no expansion.
• If the unit has no certificate of occupancy, obtain retroactive building permits from Charleston County Building Services and applicable zoning permits, which may mean updating to current building code, passing inspections, and meeting flood rules.
• Notify and obtain coordination letters from JIPSD, Charleston Water System, 911, and Charleston County Addressing.

Units built between 2012 and 2025 have no path yet. The Town labeled that group Phase 2, and no ordinance creating it had been identified as of September 28, 2026. The City of Charleston has no amnesty program identified, and Charleston County's Sol Legare overlay does not address pre-existing units.

Use the James Island list as your documentation template even outside the Town. Assemble the affidavits and tax bills now. Add utility records because they can help prove the date of construction.

Then price the retroactive permit. Account for code upgrades and flood compliance, as well as inspections. General violations run per day of continued violation under the James Island code, and an unpermitted unit also jeopardizes the insurance and 4% tax treatment discussed in the sections above.

Does North Carolina allow ADUs? How border states compare

Yes. Beginning January 15, 2027, North Carolina's ADU law requires cities with populations of 50,000 or more to allow at least one ADU for every single-family detached home in residential zones. North Carolina ratified Senate Bill 445, the "Regulatory Reform Act of 2026," as Session Law 2026-59. Governor Josh Stein signed it on August 11, 2026.

The NC General Assembly bill page shows the conference report clearing the Senate 37–0 on July 29, 2026 and the House 84–26 on August 4, 2026. A Senate concur motion had failed 0–45 in June.

Section 44 of the ratified text adds G.S. 160D-917. It bars covered cities from setting minimum parking requirements, requiring placement in a conditional zoning district, and charging fees above those for a comparable single-family permit. Size caps cannot fall below 800 or exceed 1,000 sq ft. The statute does not name owner-occupancy directly; it gets there through subsection (b)(1), which bars a city from prohibiting "the use of the primary single-family detached dwelling and the accessory dwelling for long-term rentals by separate households."

Cities may still require setbacks up to 10 feet and side-or-rear placement. They may also require an ADU to be smaller than the primary dwelling. Cities must adopt local ordinances by July 1, 2027, or the law allows ADUs without limitation.

The law excludes historic districts and National Historic Landmarks. It also excludes units lacking water and wastewater connections, and it does not override private covenants. Subsection (h) narrows it further: it reaches only cities of 50,000 or greater "that are not in the coastal area, as that term is defined in G.S. 113A-103," so North Carolina's coastal cities are outside the mandate.

South Carolina allows local governments to impose the requirements that North Carolina bars in covered cities:

• Policy dimension | North Carolina (cities of 50,000+) | South Carolina
• Statewide mandate to allow ADUs | Yes, effective January 15, 2027 | No; enabling authority only
• Owner-occupancy requirement | Barred in effect; cities cannot block long-term rental of both units | Local discretion; Charleston, Columbia, Greenville, Mount Pleasant require it
• Minimum parking | Prohibited | Local discretion; one extra space in Charleston, Columbia, Mount Pleasant
• Permit fees | Capped at comparable single-family fees | No statewide cap
• Size cap | Must fall between 800 and 1,000 sq ft | No statewide rule; local caps of 600–1,000 sq ft
• Local adoption deadline | July 1, 2027 | None

If you searched from Rock Hill or York County, you probably saw Charlotte's ADU pages first. Rock Hill sits in the Charlotte metro, and Charlotte is a covered city under SB 445, so its rules will loosen in 2027. None of that crosses the state line.

Rock Hill's ADU standards come from its own Chapter 5, and South Carolina has nothing resembling the North Carolina mandate. Broader NC bills that would have covered every municipality, HB 627 and SB 495, stalled in Rules committees in 2025.

How Steadily insures ADUs

Once a paying tenant moves into an ADU, confirm that your existing homeowners policy covers the rental use. If it does not, a fire or liability claim in the cottage can become a coverage dispute. An owner-occupied Charleston lot with a rented backyard cottage may need a landlord insurance policy that specifically names the ADU.

Steadily writes ADUs as a named property type in all 50 states. It also writes single-family rentals and multifamily properties, plus condos. Coverage is available for vacant and renovation properties and short-term rentals.

Its DP3 open-peril form is the primary tier, with liability options from $100K to $1M+. Loss of rental income can cover up to 12 months of fair rental value, capped by a sub-limit tied to dwelling coverage. A Mount Pleasant owner running the ADU as a permitted STR can be written the same way. During construction or between tenants, the vacant coverage add-on fills the gap that a standard policy's vacancy window would otherwise open.

Flood and earthquake are excluded. Other exclusions include sewer backup and intentional tenant damage. Normal wear and tear is also excluded. In the Lowcountry, that means a separate flood policy on the ADU, not an assumption that the landlord policy covers rising water.

Premiums scale with rebuild cost. Steadily's range for $100K of dwelling coverage is $500–$1,000 a year, and $300K runs $900–$1,800. The national average is near $1,478.

Steadily's ADU insurance page covers how the unit is written, and the landlord insurance in South Carolina page covers state-specific perils and pricing. Get a quote in minutes at quote.steadily.com. No phone call required.

FAQ

South Carolina has no single statewide ADU rule, so the answers below depend on your local zoning district, wastewater approval, and intended rental use. These questions summarize the main construction, occupancy, rental, size, and timing limits.

Can I build a second house on my lot in South Carolina?

Only if your county or city zoning ordinance allows an accessory dwelling unit in your district, and only if no recorded covenant on your lot bars a second dwelling. Charleston, Columbia, Greenville, and Mount Pleasant allow ADUs with conditions. James Island and Rock Hill had no confirmed standards for new units as of September 2026. The same was true of Horry County. The BZA cannot grant a variance to allow a use your district omits, so an unlisted use requires a council text amendment.

Do I need to live on the property to rent out an ADU?

In Charleston, Columbia, Greenville, and Mount Pleasant, yes. Each requires the owner to occupy either the main house or the ADU as a primary residence. Charleston records that condition as a covenant on the lot. Greenville County's current UDO did not confirm an owner-occupancy rule.

Can I rent my South Carolina ADU on Airbnb?

Mount Pleasant permits it with a Town STR permit and business license. Both units need certificates of occupancy, and remaining 2026 permits were subject to a waitlist. Charleston prohibits STR use on any lot with an ADU, and Columbia bars ADU tenancies under 30 days. Myrtle Beach excludes STRs from residential R districts other than RMV.

How big can an ADU be in South Carolina?

Published local caps reviewed here range from 600 to 1,000 sq ft. Charleston allows 850 sq ft of conditioned floor area, or a 600 sq ft footprint for detached units using setback exceptions. Columbia allows the lesser of 1,000 sq ft or half the main house, while Greenville allows 1,000 sq ft.

Mount Pleasant allows 600 to 850 sq ft by district, with no detached cap in RC-1, RC-2, and RR. Unincorporated Charleston County's Sol Legare overlay allows 800 sq ft, or up to 1,500 with a BZA special exception.

What permits do I need and how long does it take?

You need zoning approval and a building permit with plan review. Before the county issues the building permit, you also need either a paid water and sewer tap or an SCDES septic Permit to Construct.

Published plan-review targets run 3 business days in Columbia and 5 in Greenville County. Horry County publishes 7–10 working days, while Mount Pleasant publishes 4–6 weeks. SCDES sets a 90-day septic goal with no guaranteed deadline.

Builder estimates run 10–16 weeks from zoning review through utility hookup in the Upstate. Coastal OCRM review can add 30–90 days.