As of October 2026, one 2026 Florida cost guide estimates a 600 sq ft detached ADU in Miami at about $105,000 for basic finishes to $280,000 for high-end. Garage conversions usually cost less. Impact-rated openings, flood elevation and permits are the Miami-specific costs that most often move the total.
What do published estimates say?
We did not find a public source that tracks completed Miami ADU prices. The closest published figures, as of October 2026:
- Detached, 600 sq ft, Miami: about $105,000 basic, $165,000 mid-range, $280,000 high-end (CostToBuildHouse, 2026 Florida ADU cost guide).
- Garage conversion, Florida: about $60,000 to $145,000 (same guide).
- Attached ADU, Florida: about $120,000 to $200,000 (same guide).
- Detached ADU, national: about $150 to $250 per sq ft (HomeGuide).
These are publisher estimates, not bids. The Florida guide does not list its underlying data, so treat it as a rough starting point.
What makes Miami ADUs cost more than the national average?
- Hurricane code. Miami-Dade is in the High-Velocity Hurricane Zone. Approved impact windows and doors, roof systems and structural connections cost more than in most of the country.
- Flood elevation. In a flood zone, raising the floor to the base flood elevation plus one foot can mean a taller stem wall, fill, steps or a ramp.
- Utilities. Panel upgrades, a new sewer line or septic work, and a dedicated AC system are common line items.
- Fees. The county lists impact fees for unincorporated ADUs, on top of permit fees.
Is a garage conversion always cheaper?
Usually, because the slab, walls and roof already exist. The exception is a garage whose floor sits below the required flood elevation, or whose roof would need replacing to meet wind code. Then the savings shrink.
When does the price depend most on your lot?
It depends on what the lot already has. Two 600 sq ft units can differ by tens of thousands of dollars if one lot is in a flood zone, needs a new sewer connection or has no room for a crane or delivery truck. That is why we visit, measure and check the flood data before writing a price.
Related
Sources, as of October 2026: CostToBuildHouse, "2026 Florida ADU Cost Guide"; HomeGuide, "How much does it cost to build an ADU?"; Miami-Dade County ADU and guesthouse page; Florida Division of Emergency Management flood guidance. These numbers are third-party estimates, not bids from us.
Updated October 2026