An ADU builder in Charleston is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through Charleston's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in South Carolina.
What ADU Builders Cost in Charleston [7]
Based on our Charleston cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.
| New Detached ADU (all-in) | $150,000-$300,000 |
| Cost per Sq Ft | $180-$400 |
| Garage Conversion | $60,000-$150,000 |
| Prefab / Modular ADU (installed) | $100,000-$200,000 |
| City Permit & Plan Review | Valuation-based building-permit fees, no published flat ADU fee - third-party estimates put total Charleston ADU permitting at roughly $1,500-$3,000 |
| Impact Fees | No ADU-specific impact-fee schedule published - confirm current totals with the Permit Center |
For a full line-item breakdown, see our Charleston ADU cost guide. To confirm what you're allowed to build before you hire, review the Charleston ADU rules (max detached size: 850 sq ft of conditioned floor area; if using the reduced 3 ft side/rear setback exception (Sec. 54-506.f), the building footprint is capped at 600 sq ft; owner-occupancy: Required - the owner must live in either the main house or the ADU as their primary residence, enforced by a recorded Declaration of Covenants that runs with the land; if neither is owner-occupied the ADU cannot be rented separately, and the city can revoke the certificate of occupancy).
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How to Vet an ADU Builder in Charleston
- License: Confirm a current contractor's license in South Carolina and that it's in good standing. Ask for the license number and verify it with the state board.
- ADU-specific experience: Ask how many ADUs they've completed in or near Charleston and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
- Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
- Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
- Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits (Valuation-based building-permit fees, no published flat ADU fee - third-party estimates put total Charleston ADU permitting at roughly $1,500-$3,000), plan check (Standard plan review; in FEMA flood zones an elevation certificate is typically part of the permit package (lowest floor must be 2 ft above Base Flood Elevation for new residential construction since July 2020)), and impact fees (No ADU-specific impact-fee schedule published - confirm current totals with the Permit Center) are included.
- Permit handling: Confirm they manage Charleston's permit process ("Administrative conditional-use approval by the Zoning Administrator - no hearing. Three steps: (1) ADU site-plan application + draft Declaration of Covenants to the Permit Center for Planning and Legal review; (2) building permit application; (3) record the approved covenant with the county Register of Deeds - no certificate of occupancy until the recorded covenant comes back. In historic districts, BAR Certificate of Appropriateness comes first for exterior work visible from the street", typically No official published timeline - expect several weeks to a few months for zoning plus building review; BAR review and flood-zone engineering add cycles) and who is responsible if revisions are required.
- Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.
Questions to Ask Before You Hire
- How many ADUs have you built in Charleston in the last two years?
- Is your bid fixed-price, and what would trigger a change order?
- Are permits, plan check, and utility connection fees included?
- What's a realistic timeline, including permit review (No official published timeline - expect several weeks to a few months for zoning plus building review; BAR review and flood-zone engineering add cycles) and construction?
- Who is my point of contact and how are delays communicated?
- What warranty do you provide on workmanship?
- Can you share three recent South Carolina ADU client references?
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