In unincorporated Miami-Dade, often yes, if the lot and unit meet the county ADU rules. As of October 2026, the county process covers legalizing as well as building an ADU, with a building permit, site plan review, impact fees and a renewable Certificate of Use. Inside a city, that city's rules apply instead.
Which properties qualify?
The same as for a new ADU in unincorporated areas: a single-family lot of at least 7,500 sq ft in AU, EU or RU zoning inside the Urban Development Boundary, one ADU per lot, and a unit of 400 to 800 sq ft in RU-1 districts. A guesthouse over 800 sq ft cannot be used as an ADU.
What does the county require?
- A building permit to legalize the unit, with plans showing it meets the Florida Building Code.
- Administrative site plan zoning review.
- Zoning approval for any setback violation or a second nonconforming residence.
- Impact fees and an ADU owner disclosure statement.
- Proof of notice to your HOA, if you have one.
- An interior inspection, then a Certificate of Use that must be renewed.
The county also says the existing structure must be legal and not under construction when you apply.
What work is usually needed?
Most unpermitted efficiencies need some combination of hurricane-approved windows and doors, fire separation and smoke alarms, an emergency escape opening, electrical corrections and plumbing that can be inspected. Walls sometimes have to be opened so inspectors can see what was built.
Will it change my taxes?
The county notes that an ADU may raise assessed value and affect homestead status and senior exemption eligibility when rented. Ask the Property Appraiser before you finish the process.
When is legalizing not realistic?
It depends on the lot and the build quality. A lot under 7,500 sq ft, a unit over 800 sq ft, a floor below flood elevation or framing that cannot meet wind code may make legalizing impractical. Some owners convert the space back to part of the main house instead. We inspect and tell you which way makes sense.
Related
Sources, as of October 2026: Miami-Dade County ADU and guesthouse page; National Association of Counties article on the Miami-Dade ADU ordinance.
Updated October 2026