These rules apply to UNINCORPORATED Hillsborough County - communities like Brandon, Riverview, Town 'n' Country, Valrico, and Carrollwood - not the City of Tampa, which has its own separate ADU rules. The county has quietly allowed accessory dwellings since 2006 under Land Development Code Sec. 6.11.02: up to 900 sq ft of living space on lots of 7,000 sq ft or more, approved administratively against fixed standards with no public hearing. The catches are real, though - the main home must stay owner-occupied (a rule the code says cannot be varied), one ADU per lot, and principal-building setbacks apply. Florida has no statewide ADU mandate (both 2025's HB 943 and 2026's SB 48 died), so these county rules fully govern - and despite what several builder blogs claim, there is no 'SB 943 mandate' or 750 sq ft state rule.
Zoning & Size Requirements [1][2][3]
Yes — unincorporated Hillsborough County allows ADUs. A detached ADU can typically be up to the county's size limit under Florida state law and the County's zoning code.
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| Where ADUs Are Allowed | Agricultural districts (AM, A, AR, AS, ASC) and single-family RSC districts (RSC-2/3/4/6, RSC-9 with a 7,000 sq ft lot); certain RDC/RMC/SPI districts only where the parcel has an owner-occupied single-family home (LDC Sec. 2.02.02); Planned Developments follow their PD conditions |
| Max Size (Detached) | 900 sq ft of living space (measured to outside faces of exterior walls; garages, unconditioned attics, and covered patios don't count). A variance up to 1,200 sq ft or 25% of the main home's living space (whichever is less) is possible only on lots of 14,520+ sq ft |
| Max Size (Attached) | Same 900 sq ft living-space cap - the ADU may be attached or detached (same variance path on 14,520+ sq ft lots) |
| Max Size (JADU) | No JADU category - Florida has no junior-ADU framework; the 900 sq ft accessory-dwelling rules are the only path |
| Max Height | No ADU-specific cap - district height limits apply (35 ft in the RSC single-family districts). An ADU above a detached garage is allowed only where the main home is two or more stories |
| Max Units | One ADU per lot, on the same lot as the principal dwelling - cannot be varied. Other detached structures may not be used for independent living or sleeping, even for guests. |
Setback & Parking Requirements [1][2][3]
Unincorporated Hillsborough County requires a rear setback of about 25 ft for a detached ADU, and parking requirements vary by unit size or location. Owner-occupancy is required.
| Rear Setback | Principal-building setbacks apply (e.g., 25 ft rear in RSC-4, 20 ft in RSC-9) - an ADU above a detached garage may use accessory-structure side/rear setbacks instead |
| Side Setback | Principal-building side setbacks (7.5 ft in RSC-4, 5 ft in RSC-9) |
| Front Setback | Principal front setback; a detached ADU placed in a functional front yard must sit back twice the required front-yard depth or 50 ft (whichever is less) - a rule that cannot be varied |
| Parking Required | No ADU-specific requirement in the county parking schedule (single-family homes need 2 spaces) - confirm any added-space interpretation with Development Services |
| Owner Occupancy | Required and non-variable: the principal single-family home on the lot must be owner-occupied (LDC 6.11.02.B - 'these requirements shall not be varied') |
| Min Lot Size | 7,000 sq ft minimum lot (conforming or legal non-conforming), unless a Planned Development expressly permits smaller; 14,520+ sq ft to seek the size variance |
Permit Process & Fees [4]
An ADU in unincorporated Hillsborough County is approved administratively — no public hearing — within a standard building-permit review cycle (no published ADU-specific timeline); permit fees are standard county building-permit plus impact/mobility fees (no ADU-specific schedule published - get an estimate from Development Services before budgeting).
| Approval Process | Administrative 'Conditional Use' - approval against the fixed standards of LDC Sec. 6.11.02 through standard development/building-permit review, with NO public hearing. Apply through the HillsGovHub permit portal; size variances go through the county variance process |
| Review Timeline | a standard building-permit review cycle (no published ADU-specific timeline) |
| Permit Fees | standard county building-permit plus impact/mobility fees (no ADU-specific schedule published - get an estimate from Development Services before budgeting) |
| Impact Fees | County impact and mobility fees apply to new dwelling space - no ADU exemption exists in Florida; confirm current amounts with Development Services |
| Plan Check | Standard plan review via HillsGovHub; the 900 sq ft living-space measurement (exterior-wall faces, excluding garage/patio) is worth confirming on your drawings up front |
| Pre-Approved Plans | No county pre-approved ADU plan program as of mid-2026 |
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Construction Costs [5]
Building an ADU in unincorporated Hillsborough County typically costs $130,000-$260,000 (Tampa-metro market estimate) ($170-$330 (market estimate) per sq ft); a garage conversion runs $65,000-$150,000 (market estimate).
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Construction costs in unincorporated Hillsborough County mirror the surrounding Inland Empire market. Rural parcels can cost more due to septic, well, access, and fire-hazard (WUI) requirements, so treat these as planning ranges and get local bids.
| Average Build Cost | $130,000-$260,000 (Tampa-metro market estimate) |
| Cost per Sq Ft | $170-$330 (market estimate) |
| Garage Conversion | $65,000-$150,000 (market estimate) |
| Prefab ADU (Installed) | $100,000-$220,000 (market estimate) |
Finance Your ADU Project
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Rental Income Potential [6]
| Avg Rent (1 Bedroom) | $1,250-$1,750/mo (Tampa-metro market) |
| Avg Rent (2 Bedroom) | $1,550-$2,250/mo |
| Short-Term Rental | The county ADU ordinance doesn't restrict short-term rental, and Florida preempts post-2011 local vacation-rental bans - but state DBPR licensing and tourist taxes apply under 30 days, and the main home must stay owner-occupied |
| Est. Annual ROI | 6-8% annual return (market estimate) |
Recent Law Changes
What's Changed Recently
- No county ADU code changes since Ordinance 20-17 (effective October 2020, which added the front-yard placement rule); the code is current through Ordinance 25-43 (August 2025) with Sec. 6.11.02 unchanged
- 2025: Florida's statewide ADU mandate attempt HB 943 died (laid on the table April 29, 2025); the Live Local Act amendments that passed instead contain no ADU mandate
- 2026: successor bill SB 48 (ADUs in all single-family zones) advanced in the Senate but died in March - Florida still has no statewide ADU mandate, so the county's 2006-era rules fully govern; watch for a 2027 refile
- Accuracy note: builder and prefab marketing blogs widely claim a 'Florida SB 943' ADU mandate 'effective July 1, 2025' with 750 sq ft caps - no such law passed; the county's 900 sq ft and owner-occupancy rules remain in force
Tips for Building an ADU in Unincorporated Hillsborough County
- Brandon, Riverview, Town 'n' Country, Valrico, and Carrollwood are unincorporated - these County rules apply, not City of Tampa rules (Tampa's ADU program covers designated city neighborhoods only)
- The owner-occupancy rule is non-negotiable - the code explicitly bars variances - so an ADU here works for family or rental income only while you live in the main house
- Measure the 900 sq ft to the outside faces of the exterior walls, excluding the garage and covered patios - a design that reads '900 sq ft' inside may bust the cap outside
- Lot at least 14,520 sq ft (a third of an acre)? You can seek a variance up to 1,200 sq ft or 25% of the main home's size
- Don't trust blog posts citing 'SB 943' or a Florida 750 sq ft state rule - the mandate never passed; check the county code or this page's sources
ADU Builders in Hillsborough County
Looking for an ADU builder in Hillsborough County? ADU projects need a contractor experienced with local zoning, the permit process, and utility connections — not every general contractor has built one. We match Hillsborough County homeowners with experienced local ADU contractors who provide free, no-obligation quotes. Getting at least three bids typically saves 20-40% on the same scope.
Cities Within Hillsborough County
If your property is inside one of these incorporated cities, follow that city's ADU code — not the County rules above:
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- Hillsborough County LDC Sec. 6.11.02 - Accessory Dwelling Standards Planning Department — Accessed 2026-07-30
- Hillsborough County LDC Sec. 2.02.02 - Allowable Uses in Zoning Districts Planning Department — Accessed 2026-07-30
- Hillsborough County LDC Sec. 6.01.01 - District Area, Height, Bulk and Placement Schedule Planning Department — Accessed 2026-07-30
- Hillsborough County - Residential Accessory Structure Requirements (HillsGovHub) Planning Department — Accessed 2026-07-30
- Angi - ADU Construction Cost Data Market Data — Accessed 2026-07-30
- HUD Fair Market Rents Government Data — Accessed 2026-07-30
- F.S. 163.31771 - Accessory dwelling units (permissive state framework) Government Data — Accessed 2026-07-30
- Florida Senate - SB 48 (2026) bill analysis Government Data — Accessed 2026-07-30
Frequently Asked Questions
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