County · Florida
ADU rules in St. Johns County
These are the primary sources for accessory dwelling unit regulations in St. Johns County: the county's own zoning code, planning department pages, and permit guides. Start here before talking to anyone: the rules below are what your permit reviewer will apply.
Unincorporated areas only
County zoning applies only outside city limits. If your property is inside a city or town, that municipality's own ADU ordinance governs instead, even though it sits within St. Johns County.
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The LDC defines an Accessory Family Unit as living quarters located within the main use Structure or on the same Lot as the main use Structure, and Sec. 2.02.04.B allows accessory uses to be situated on the same Lot with, but detached from, the principal use. A detached unit must meet the same required yards as the main structure. If a manufactured/mobile home is used as the unit, the lot must be at least 2 acres and zoned to allow a manufactured/mobile home.
Land Development Code Sec. 2.02.04.B.16.e-f; Art. XII definition of Accessory Family UnitAn Accessory Family Unit may be contained within the main use Structure; when it is, it must be constructed with permanent interior accessibility from the main use portion of the structure.
Land Development Code Sec. 2.02.04.B.16.jSec. 2.02.04.B.16.d caps the unit at the lesser of thirty five percent (35%) of the square footage of the main use Structure, up to two thousand (2,000) square feet of living quarters, except that the Accessory Family Unit may be at least eight hundred (800) square feet. The 800 sq ft clause acts as a floor for small homes where 35 percent would fall below 800 sq ft.
Land Development Code Sec. 2.02.04.B.16.dThe unit is limited to Family members of the owner(s) of the main use Structure, which must be declared, and continue to be declared, as homestead by the Property Appraiser. A homestead declaration requires the owner to reside on the property, so the main home must be the owner's primary residence.
Land Development Code Sec. 2.02.04.B.16.aSec. 2.02.04.B.16.g requires the Accessory Family Unit to provide adequate parking as reasonably determined by the County Administrator. The provision sets no numeric parking ratio for the unit.
Land Development Code Sec. 2.02.04.B.16.gAn Accessory Family Unit is an allowable Accessory Use in all residential and OR (Open Rural) zoning districts, subject to continual compliance with the listed conditions; no special use permit is required. Review of accessory uses is the same as required for the principal use, and the unit must comply with all other zoning and permitting requirements.
Land Development Code Sec. 2.02.04.B.16 and Sec. 2.02.04.A.1Sec. 2.02.04.B.16.b states the unit shall be non-rental and shall not be sold separately from the main use Structure, and B.16.a limits occupancy to Family members of the owner(s). Family is defined in Article XII as persons related by blood, marriage, adoption, legal guardianship, or a similar formal caregiving relationship recognized by Florida law, allowing an additional group of up to three unrelated persons. This is an in-law suite allowance, not a rentable ADU: neither long-term nor short-term rental of the unit is permitted.
Land Development Code Sec. 2.02.04.B.16.a-b; Art. XII definitions of Accessory Family Unit and FamilyThe fine print: 6 caveats that can change the picture
- St. Johns County calls this use an Accessory Family Unit; it is an in-law suite provision for family of the homesteaded owner, not a rentable accessory dwelling unit, and the code contains no separate rentable-ADU pathway
- These county rules apply only in unincorporated St. Johns County; St. Augustine, St. Augustine Beach, and other municipalities have their own codes
- The unit is not counted as a separate Dwelling Unit only while all conditions are continually met; discontinuance of the use triggers full compliance with the Land Development Code (Sec. 2.02.04.B.16.i)
- The unit must sit on the same lot as the main home and cannot be subdivided onto a separate lot (Sec. 2.02.04.B.16.c)
- A manufactured/mobile home used as the unit requires a minimum 2-acre lot and zoning that allows manufactured/mobile homes (Sec. 2.02.04.B.16.f)
- A separate Guest House accessory use (Sec. 2.02.04.B.2) allows only intermittent occupancy by non-paying guests (max 30 days per tenant per calendar year, limited kitchen, no rental) and is distinct from the Accessory Family Unit
Summarized from St. Johns County's ordinance text, read July 2026; every row links the code section it came from. Rules often vary by zone and lot, so treat this as orientation, not a permit determination, and confirm with the planning department before you commit to a design.
ADU regulations
Florida statewide law also applies
Florida sets baseline ADU rights at the state level. Where local rules are stricter than state law allows, state law usually wins, so both are worth reading.
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