Hillsborough County

Permits for ADUs on unincorporated Hillsborough County parcels are issued by Hillsborough County Development Services, which combines zoning, building, and floodplain review under one intake. Unincorporated Hillsborough is the second-largest unincorporated population in Florida and includes many dense suburban communities that operate de facto like cities. Incorporated municipalities (Tampa, Temple Terrace, Plant City) handle their own permits.

Process overview: A Hillsborough County ADU permit is a combined zoning/building review: (1) pre-application zoning determination to confirm the district permits the accessory unit and the applicable size/setback/owner-occupancy conditions; (2) site plan, floor plan, and construction drawings via Accela; (3) zoning and floodplain review (unincorporated Hillsborough has significant AE-zone exposure along the Alafia, Hillsborough, and Little Manatee rivers and around Tampa Bay); (4) building-code plan review against the Florida Building Code 8th Edition (2023); (5) mechanical/electrical/plumbing sub-permits; (6) issuance, inspections, CO.

Impact fees: Hillsborough County assesses school, transportation, parks, and fire impact fees per the adopted schedule; ADUs on existing single-family parcels face a reduced assessment relative to a new single-family dwelling unit. (schedule)

The Hillsborough County Property Appraiser maintains parcel-level assessment records for all real property in Hillsborough County, including parcels within Tampa, Temple Terrace, and Plant City. ADU additions are assessed as improvements to the host parcel. Florida's Save Our Homes 3% cap applies to the primary dwelling's assessment; ADU improvements are added at full just value in the completion year. § 193.703 FS 'granny-flat' 20% assessment reduction is available for qualifying senior-family additions on application.

Assessment policy: Building-permit data from Development Services feeds the Property Appraiser. Homestead exemption remains on the owner-occupied primary dwelling; ADUs do not carry independent homestead unless owner-occupied.

Hillsborough County administers flood, coastal-high-hazard, airport-approach, and wellhead-protection overlays that cut across jurisdictions. Tampa Bay and three major river systems (Hillsborough, Alafia, Little Manatee) produce extensive AE-zone coverage, and the Tampa International Airport approach zones constrain height across much of the western half of the county.

• FEMA Special Flood Hazard Areas (SFHA) — AE- and VE-zone mapping is extensive along Tampa Bay, the Hillsborough River, the Alafia River, the Little Manatee River, and associated tributaries. ADUs in SFHA require elevation above BFE plus county freeboard, flood vents, and flood-resistant materials. VE-zone exposure on Tampa Bay produces pile-foundation or breakaway-wall requirements on affected parcels.
• Coastal High Hazard Area (CHHA) — Under state law, the CHHA is the area below the elevation of the Category 1 storm surge line as defined by the SLOSH model. Hillsborough's CHHA covers substantial portions of the Tampa Bay shoreline and limits certain intensification of residential development; ADUs in CHHA face heightened review under the Coastal Element of the comprehensive plan.
• Tampa International Airport (TPA) Approach & Height Zoning — Parcels within TPA approach and transitional surfaces face height limitations. A two-story ADU may require FAA Form 7460 notice on high-exposure parcels; the practical effect on one-story accessory units is limited.
• Southwest Florida Water Management District (SWFWMD) Wellhead Protection — Hillsborough parcels within mapped wellhead-protection zones face enhanced septic-siting review. Many unincorporated eastern Hillsborough parcels are on private septic and are affected.
• MacDill Air Force Base Accident Potential & Noise Zones — South Tampa parcels near MacDill AFB fall within Air Installation Compatible Use Zones (AICUZ) with accident-potential and noise-attenuation requirements. New residential construction — including ADUs — in designated APZ areas is restricted; parcels in the noise-attenuation zone require sound-insulating construction.
• Wildland-Urban Interface (WUI) — Practical WUI exposure in urbanized western Hillsborough is low. Eastern Hillsborough rural tracts abutting undeveloped pine flatwoods are higher-hazard; enforcement intensity is still maturing.