ADU rules in North Charleston

Since Ord. No. 2025-002 (adopted 1-30-2025), a detached accessory dwelling unit is a listed conditional use in the R-1 Single-Family Residential district, and the R-1A, R-2 and R-3 districts carry every R-1 use, so it is allowed citywide on residential lots of at least 4,500 square feet, one per lot. North Charleston's 'conditional uses' are uses 'permitted ... subject to the stated conditions' checked by the zoning administrator, not a board hearing. The code defines an ADU as 'a separate, detached dwelling unit', and existing accessory buildings may be converted even if they are nonconforming as to height or setbacks. In the Olde North Charleston Historic and Neighborhood Conservation Districts the R-1 condition does not apply; those overlays separately allow one apartment over a detached garage.

The ADU provisions cover only detached units: §3-2 defines an accessory dwelling unit as 'a separate, detached dwelling unit', so an internal or attached apartment in a single-family home in R-1 is not an ADU and has no permit route there. A second unit inside or attached to a house is possible only as a duplex, which is a permitted use in the R-2 Multi-Family district (and in R-3, which allows all R-2 uses), subject to the R-2 lot area of 1,500 square feet per multi-family unit. In the Olde North Charleston overlays the only accessory unit form named is an apartment over a detached garage.

The ADU must be subordinate to the principal dwelling: no more than two-thirds of the principal dwelling's size and never more than 800 square feet. In the rear yard (which accessory buildings and ADUs may cover up to 40 percent of), the ADU may not exceed the height of the existing residence and must sit at least 6 feet from the house, 3 feet from interior lot lines and 5 feet from any right-of-way; an ADU above a detached garage may reach 24 feet to the ridge when the house is a single story. The lot must be at least 4,500 square feet, with one ADU per lot. Side-yard placement is possible only when the zoning administrator finds the rear yard impracticable, and ADUs are barred from front yards.

Neither the ADU conditions in §5-1(b)8 nor the §3-2 definition require the owner to live on the property, at application or afterward. Owner occupancy matters only in the short-term rental rules (room rentals in owner-occupied homes assessed at the 4 percent ratio are exempt from the STR permit cap), and ADUs are barred from STR permits altogether. South Carolina has no state ADU statute, so the local text is the whole rule.

Condition (v) requires 'one (1) additional off-street parking space' on the lot for the ADU, on top of what the principal dwelling needs. The code allows no waiver for transit proximity or street parking.

ADUs are a 'conditional use' that the code defines as permitted 'under conditions specified in the zoning ordinance'. The zoning administrator reviews the objective conditions (lot size, size cap, parking, setbacks) with the building permit under §7-1. Unlike public recreation facilities in the same list, the ADU entry calls for no council or board hearing. In the Olde North Charleston Historic and Conservation overlays, an apartment over a detached garage also needs a historic district or conservation district permit, which the planning director approves when the design standards are met (§10-30).

Condition (vi) of the ADU use states that 'ADUs shall not be eligible for short-term rental permits', so an ADU may not be rented for stays of 29 consecutive days or fewer. Nothing in the code restricts long-term rental of an ADU or requires the owner to live on site, and the definition lets an ADU have its own electric, gas, water and sewer meters. For the principal home, STRs are a conditional use under §4-21: an annual city STR permit ($350, renewal $250), a business license, accommodations taxes, at most 8 guests, off-street parking, and a cap of 60 permits per council district (owner-occupied room rentals are exempt from the cap). The code does not address selling an ADU separately; the conditions tie it to one lot with its principal dwelling.