ADU Permit Requirements in St. Johns County, FL
St. Johns County Building Services issues all residential permits (building, electrical, mechanical, plumbing, roof, pool) for unincorporated county land outside the City of St. Augustine and City of St. Augustine Beach. Codes in force: Florida Building Code 8th Edition (2023) residential and building, NEC 2020, ASCE 7-22 wind design. County is in the wind-borne debris region (not HVHZ, which is only Miami-Dade and Broward). Impact-rated windows and doors or approved storm shutters required for residential openings. Septic permits handled by Florida Department of Health in St. Johns County at (904) 506-6081. Driveways on county roads go through St. Johns County Road and Bridge; driveways on US-1 or I-95 require FDOT approval. Historic district overlays may apply in some areas. Licensed FL CILB contractors required for most trades; owner-builder allowed under F.S. 489.103(7) for homesteaded primary residence with personal supervision affidavit.
By Joey, Founder · Last verified April 20, 2026 · How we research →
When you need a ADU permit in St. Johns County
A detached accessory dwelling unit (ADU) requires building, plumbing, electrical, and mechanical permits. Confirm ADUs are allowed in the parcel's zoning district with St. Johns County Building Services at (904) 827-6800. Septic capacity must be reviewed by the Florida Department of Health in St. Johns County at (904) 506-6081.
An attached ADU (in-law suite, garage conversion with kitchen) requires building, plumbing, and electrical permits. Septic capacity must be reviewed by the Florida Department of Health in St. Johns County at (904) 506-6081 if on septic.
ADU Permit Costs: St. Johns County vs. Nearby
St. Johns County comes in on the low side for Florida. You're looking at $500 – $2,000 here, compared to the state average of $765 – $3,983.
| City | Estimated Fee |
|---|---|
| St. Johns County | $500 – $2,000 |
| Jacksonville | $500 – $5,000 |
| Miami | $500 – $5,000 |
| Tampa | $500 – $5,000 |
Fees shown are estimates based on local building code data. Actual fees may vary based on project scope and valuation. See all St. Johns County permit costs →
Zoning & HOA Considerations
ADU regulations vary dramatically by state and city. Many states (CA, OR, WA) have preemption laws that override local zoning restrictions. Check both state law and local zoning before designing.
If you live in an HOA community: hOAs have traditionally restricted ADUs, but state preemption laws in CA, OR, WA, and other states now limit HOA authority over ADUs. Check your state's ADU laws, your HOA may not be able to block construction even if CC&Rs appear to prohibit it.
Estimated Project Timeline in St. Johns County
Here's a typical timeline for a adu project in St. Johns County, FL:
Timeline is based on St. Johns County's typical about 4 weeks permit processing time. Actual timelines vary by project complexity, completeness of application, and current department workload.
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Frequently Asked Questions
Estimated permit fees for ADU projects in St. Johns County, FL range from $500 – $2,000. Fees vary based on project scope and valuation.
It depends on the specifics of your project. Some smaller ADU projects may be exempt from permit requirements, while larger ones typically require a permit. Use our free lookup tool to check your specific situation.
Working without a required permit in St. Johns County can result in fines, stop-work orders, being required to remove completed work, and complications when selling your home. It's always best to check first.
Typical approval time for ADU permits in St. Johns County is about 4 weeks. More complex projects may take longer if plan review is required.
If you live in an HOA community, you may need architectural review approval in addition to a building permit. HOA rules and city building codes are separate, you may need to satisfy both. Review your CC&Rs and submit to your HOA's architectural review committee before starting work.
Learn More About ADU Permits
Read our complete guide covering permit requirements, costs, common exemptions, and the application process.
Read ADU Guide →