ADU interest is growing in Florida. Tight housing supply, insurance-driven costs and demand for multigenerational space have kept accessory dwelling units popular, even as rents in Miami, Tampa and Orlando have flattened or dipped in 2025–26. Tampa, for example, reports 28 ADU applications and 7 completions since expanding its program in 2024. But the question every homeowner and investor asks first is the same: how much does it actually cost?
Below is what we're seeing on Hivesta bids and projects from 2025–26 — not internet averages. These numbers assume a permitted, code-compliant build with a licensed general contractor.
Florida ADU costs at a glance
| ADU Type | Typical Size | All-In Cost | Per Sqft |
|---|---|---|---|
| Garage conversion | 400–600 sqft | $70K – $130K | $160 – $230 |
| Attached ADU (addition) | 500–800 sqft | $120K – $220K | $220 – $290 |
| Detached ADU (stick-built) | 600–1,000 sqft | $160K – $310K | $240 – $340 |
| Detached ADU (prefab) | 400–900 sqft | $110K – $240K | $200 – $280 |
What actually drives the cost?
1. Site conditions
Sloped lots, removal of large trees, septic upgrades, and underground utility runs from the main panel are the most common cost surprises. A flat, in-fill lot in an urban Florida neighborhood will almost always come in at the low end of our range.
2. Foundation & connection type
Detached ADUs need their own foundation and utility tie-ins (water, sewer, electric, sometimes gas). Attached ADUs share walls and utilities with the main home — often $30K–$60K cheaper in our projects as a result.
3. Finish level
A rental-grade finish (LVP floors, IKEA-style cabinets, builder-grade fixtures) versus a luxury short-term rental finish (quartz, custom cabinetry, designer lighting) can swing the budget by $40–$80 per square foot in our experience.
4. Prefab vs. stick-built
Modular and panelized prefab options (we partner with HapiHomes for several of these) can cut overall schedules by roughly 20–50% (McKinsey) and lock in pricing earlier. Site prep and permitting costs don't change much, but the structure itself is faster and more predictable.
Permits and timeline
- Building permit review: often 6–14 weeks once the application is complete (Miami-Dade and Broward trend longer). Florida law (s. 553.792) gives local building departments 30 business days to act on a complete single-family permit under 7,500 sqft. Zoning review and resubmittals add time, so total approval can run several months; our city pages give local ranges.
- Site work + foundation: 3–5 weeks.
- Vertical construction (stick-built): 12–20 weeks.
- Vertical construction (prefab): 4–8 weeks once on-site.
- Total project time: typically 6–10 months from contract to certificate of occupancy on Hivesta projects (phase durations above are typical in our experience).
ROI: what does an ADU actually return?
In our Florida markets, a permitted ADU typically rents for $1,200–$2,500/month long-term, depending on metro and size (2026 listing data). Short-term rental income varies widely by market and local STR rules, and many cities restrict STRs, so model it with AirDNA or local comps. On a $180K all-in build, those long-term rents pencil out to roughly an 8–17% gross yield; net yield after property taxes, insurance and maintenance is materially lower. ADU comps are also increasingly available to appraisers, which can support property value.
Common mistakes to avoid
- Skipping the feasibility study. Zoning, setbacks, and impact fees vary block-by-block.
- Using a contractor who's never permitted an ADU in your specific city. Each jurisdiction has quirks.
- Under-budgeting utilities. Bringing a new sewer lateral can run $8K–$20K.
- Choosing finishes for resale instead of rental. Renters wear out high-end finishes fast.
- Not running the rental numbers before you build. Build for the cash flow, not the look.
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Frequently asked
Are ADUs legal everywhere in Florida?
No single statewide rule applies. Florida law lets, but does not require, cities and counties allow ADUs (s. 163.31771), so rules are set locally. For example, the City of Orlando and unincorporated Miami-Dade allow them broadly, while the City of Tampa limits them to certain neighborhoods. A 2026 bill to require ADUs statewide (SB 48) did not pass. Setbacks, height limits, and parking requirements also vary by city. A feasibility study confirms what's allowed on your exact parcel.
Can I finance an ADU?
Yes. Most homeowners use a HELOC, cash-out refi, construction-to-perm loan, or a renovation loan. Some lenders now underwrite the projected ADU rental income as part of qualifying. FHA, for example, counts 75% of estimated rent from an existing ADU, and 50% of projected rent for an ADU built under a Standard 203(k).
How long does an ADU take to build in Florida?
On typical Hivesta projects, plan on 6–10 months from signed contract to certificate of occupancy, with permitting being the most variable phase.
Is prefab cheaper than stick-built?
It can be — up to roughly 20% cheaper on the structure in some cases, but savings aren't guaranteed, and McKinsey notes overruns of up to 10% when logistics or materials go wrong. The bigger win is usually speed and price certainty.
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