Accessory dwelling units are one of the fastest-growing project types in St. Johns County. Whether you call it a guest house, in-law suite, mother-in-law apartment, or ADU, the concept is the same: a separate living space on your existing property. Wilson & Co designs and builds ADUs across St. Johns County — from compact garage conversions in Nocatee to full detached guest houses in St. Augustine.
Are ADUs Legal in St. Johns County?
Yes, with conditions. St. Johns County allows accessory dwelling units in most residential zoning districts. Key requirements include:
- Size limit: Typically 50% of the primary dwelling’s heated square footage or 1,000 square feet, whichever is less
- Setbacks: Must meet standard setback requirements for your zoning district (typically 25’ front, 7.5’ side, 20’ rear)
- Height: Generally limited to 35 feet or the height of the primary dwelling
- Parking: One additional off-street parking space may be required
- Owner occupancy: The property owner must occupy either the primary dwelling or the ADU
- Utilities: Must connect to the same utility services as the primary dwelling (separate metering may be available)
These requirements are subject to change. Wilson & Co researches the current regulations for your specific parcel before beginning design.
ADU Types We Build
Detached Guest Houses
A standalone structure built from the ground up on your property. This provides the most privacy and flexibility but costs the most and requires the most lot space.
Cost: $150-$300 per square foot Size range: 400-1,000 sq ft Timeline: 4-6 months construction after permitting
Garage Conversions
Converting an existing attached or detached garage into living space. The most cost-effective ADU option since the structure, roof, and foundation already exist.
Cost: $50,000-$100,000 Timeline: 2-3 months construction
Attached In-Law Suites
A new addition to your existing home with a separate entrance, kitchenette, and bathroom. Shares a wall with the main house but functions as an independent unit.
Cost: $100,000-$200,000 Timeline: 3-5 months construction after permitting
What Does an ADU Cost in St. Johns County?
| ADU Type | Size | Cost Range |
|---|---|---|
| Garage Conversion | 400-600 sq ft | $50,000–$100,000 |
| Attached Suite | 500-800 sq ft | $100,000–$200,000 |
| Detached Guest House | 500-1,000 sq ft | $90,000–$275,000 |
These costs include design, permitting, construction, and all finish work. They do not include furniture, landscaping, or separate utility metering (if desired).
The ADU Building Process
- Feasibility study — We research your lot’s zoning, setbacks, utility access, and HOA rules to confirm an ADU is buildable
- Design — Architectural plans optimized for your lot, including floor plan, elevations, and material selections
- Permitting — Complete permit package submission to St. Johns County including engineering, impact fee calculation, and utility coordination
- Construction — Ground-up build or conversion, including foundation, framing, mechanical systems, and interior finishes
- Certificate of Occupancy — Final inspections and CO issuance, making the unit legally habitable
Can I Rent My St. Johns County ADU?
Long-term rental is generally permitted in most St. Johns County residential zones. Short-term rental (less than 30 days) may face additional restrictions depending on your specific location and any HOA rules. Always verify current regulations before planning a rental ADU.
Start Your ADU Project
Call Wilson & Co at (904) 792-6175 for a free feasibility consultation. We will research your property’s ADU potential and provide a preliminary cost estimate.
Ready to Start Your Project?
Contact Wilson & Co Design Build for a free consultation on your remodeling project.