Short answer: In the Town of Mount Pleasant, the kitchen decides it. A finished room over a garage (FROG) is livable space without a kitchen, and the Town says it can have its own sleeping and bathroom areas. Once the space has its own outdoor entrance and its own kitchen and bathroom, the Town treats it as an accessory dwelling unit (ADU), which brings zoning conditions, a recorded covenant and, where it applies, the Town's Building Permit Allocation System. Either way, a permit expires if work does not start within 180 days of issue or stops for 180 days.
Where the Town draws the line
The Town of Mount Pleasant's Building Inspection FAQ defines an ADU as a separate living arrangement within, attached to or detached from a house, with "its own dedicated entrance from the outdoors and a kitchen and bathroom separate from those contained within the principal structure". A FROG is "livable space over a garage that does not contain a kitchen", and it "can have dedicated sleeping and bathroom areas".
The kitchen test is broader than most people expect. The Town says a range, an oven, or a utility connection suitable for one establishes a kitchen, but that it is "no longer the sole factor" in deciding whether a space is an ADU; the definition it quotes is an area used or designated for preparing food, and every kitchen area has to have a sink. Leaving the range out of a plan with a food-prep counter, a sink and an outside door does not automatically make it a FROG. Ask the Town before the plans are drawn.
What you can settle yourself first
- Check your covenants. The Town says ADUs must be allowed by your neighborhood covenants and restrictions, and tells owners to check with the HOA. For an ADU it also requires a signed Recorded Covenant Affidavit certifying that no covenant prohibits one.
- Check your zoning and neighborhood. The Town's ADU handout lists the zoning districts where ADUs are allowed, and names the Planned Development neighborhoods that allow them: Carolina Park, Cassina Plantation, Central Mount Pleasant, I'On, Pepper Tract (including Pepper Plantation and Tupelo), Pinckney Place, Seaside Farms, Wando Farms and Watermark.
- Email the Building Inspection Division. The Town invites exactly this question at [email protected] or 843-884-5184. You do not need to hire anyone to ask whether your plan is a FROG or an ADU.
When it becomes an ADU: the extra rules
The Town's ADU handout, quoting its zoning code, sets conditions a FROG does not have:
- One ADU per lot, subject to lot coverage.
- A conditioned floor area limit (the handout says 850 square feet); for an ADU above a detached garage, the handout says the garage footprint limits take precedence.
- A height limit for detached ADUs (the handout says 25 feet).
- One extra off-street parking space.
- A recorded covenant that the house or the ADU is owner-occupied as the owner's primary residence, that no more than three people live in the ADU, and that the property is never converted to a horizontal ownership regime.
- Building plans signed and sealed by a South Carolina registered design professional.
Handouts change, so confirm the current numbers with the Department of Planning before you design around them.
The allocation system and the 180-day clock
Mount Pleasant's residential Building Permit Allocation System (BPAS), started January 8, 2019, runs six-month allocation cycles that include accessory dwelling units, with half of each year's allocation opening January 1 and half July 1, first come, first served; Carolina Park and Liberty Hill Farms are excluded. Under BPAS, an application listing the contractor as "to be determined" is not accepted. The Town's BPAS page describes the program as running five years from 2019 and also as currently operating, so ask the Division whether your ADU needs an allocation today.
The expiry rule applies to every permit. The Town's FAQ says a permit becomes invalid if work does not start within 180 days of issue, or if it sits inactive for 180 days; outside the allocation program the Building Official can grant 180-day extensions, while an allocation permit is voided and you reapply. A garage apartment that stalls for six months can go back to the start of the queue.
What is left after the trade fix
A room over a garage needs framing, a plumber, an electrician and HVAC. Somebody still has to decide early whether the plan is a FROG or an ADU, get covenant and zoning sign-off, have the plans sealed where the Town requires it, keep the permit active so it never hits the 180-day line, and coordinate every inspection through the final. That is the general contractor's job. See our in-law suites page and the Mount Pleasant permit guide.
Local notes: fees and owner-builders
The Town bases building permit fees on the total cost of construction, including materials, labor, overhead and profit, and says impact fees may apply. You can act as your own builder only after recording a Non-Licensed Builder Disclosure at the Register of Deeds, and not if the house is deeded to a trust, LLC or similar entity. The Town also warns that if a contractor asks the homeowner to pull the permit, "we advise that you reconsider". The SC licensing threshold explains who needs a licence.
Sources
- Town of Mount Pleasant — Building Inspection Division FAQ (FROG vs ADU, 180-day expiry, owner-builder, fees): tompsc.com/1111/Frequently-Asked-Questions…
- Town of Mount Pleasant — Building Permit Allocation System: tompsc.com/1100/Building-Permit-Allocation…
- Town of Mount Pleasant — Accessory Dwelling Unit requirements and plan review checklist: tompsc.com/DocumentCenter/View/1116/Planni…
General guidance for homeowners in Charleston and York County, South Carolina, written from what we see on jobs. Conditions vary house to house; anything structural, gas or electrical is licensed work in South Carolina and should be looked at in person.
Frequently Asked Questions
Can a FROG in Mount Pleasant have a bathroom?
Yes. The Town defines a FROG as livable space over a garage without a kitchen, and says it can have dedicated sleeping and bathroom areas.
What makes a room over a garage an ADU in Mount Pleasant?
Its own dedicated entrance from the outdoors plus its own kitchen and bathroom, separate from the main house, so it functions as a complete living unit. A range, an oven or a range hookup establishes a kitchen, but the Town says that is no longer the only factor.
Do Mount Pleasant ADUs need a permit allocation?
The Town's Building Permit Allocation System lists accessory dwelling units as an allocated category, excluding Carolina Park and Liberty Hill Farms. The program was described as running five years from January 2019, so confirm with the Building Inspection Division whether your ADU needs an allocation now.
How long is a Mount Pleasant building permit good for?
A permit expires if work does not begin within 180 days of issue or after 180 days of inactivity. Permits outside the allocation program can be extended in 180-day increments by the Building Official; allocation permits are voided and must be reapplied for.