What's Required in Miami
- Allowed by right on single-family lots in T3-L, T3-O, T4, T5, T6, CI-HD and D1; not in T3-R (Miami 21 Table 3, Section 3.18)
- Size: minimum 275 / 450 / 550 square feet by bedrooms; maximum 10 percent of lot area up to 800 square feet detached or 500 square feet attached, no Waiver
- Detached unit at the ancillary setbacks (5 feet side and rear, 20 feet front in T3); two-story detached units 10 feet from the house; no taller than the house
- Separate entrance not facing the street; house designed as one single-family residence; clerestory windows only, max 24 inches, on upper walls abutting neighbors
- One parking space per ADU, none within a TOD or transit corridor
- Master building permit at 0.5 percent of cost plus electrical, plumbing and mechanical trade permits, $40 application each, $0.11 per square foot energy surcharge, $105 certificate of occupancy
- City impact fees per new dwelling unit (single-family detached row: $164 police, $704 fire, $413 general services, $6,818 parks) plus county road and school impact fees
- Same ownership as the house, predominately permanent housing; rental only with homestead and a $300 registration renewed yearly at $250
- Contractor must hold a Florida license or Miami-Dade certificate of competency, or the owner files as owner-builder under FS 489.103(7)
Can You Build an ADU in Miami?
Yes, since Ordinance 14375 rewrote the Miami 21 rules effective October 1, 2025. An Ancillary Dwelling Unit is a second unit with its own sleeping and living area, bathroom and kitchen, allowed by right on any lot with a single-family residence in T3-L, T3-O and every T4, T5 and T6 zone (plus CI-HD and D1), but not in T3-R. It does not count toward density. Sizes come from Article 6, Table 13: a minimum of 275 square feet for an efficiency, 450 for one bedroom and 550 for two, and a maximum of 10 percent of the lot area, capped at 800 square feet detached or 500 square feet inside or attached to the house, with no Waiver of the maximum. The ADU may sit inside the house or in an Ancillary Building at the ancillary setbacks (5 feet side and rear, 20 feet front in T3); a two-story detached building needs 10 feet of separation and is limited to two stories, one in T3-R, never taller than the house. It needs its own entrance not facing the street, second-story walls abutting a neighbor may have only clerestory windows no more than 24 inches high, and one parking space is required unless the lot is in a TOD or transit corridor.
The house and ADU stay under one ownership, the ADU must be predominately permanent housing, and it may be rented only while the property has homestead status, with annual registration under City Code 2-214.
Miami ADU Permit Rules by Scenario
| What you are doing | City filing | Rule |
|---|---|---|
| Detached ADU up to 800 sq ft on a T3-L, T3-O or T4-T6 single-family lot | Master building permit + electrical, plumbing and mechanical trade permits | Miami 21 Table 3 and 3.18; City Code 10-18 |
| ADU inside the house or attached, up to 500 sq ft | Building permit with trade permits | Miami 21 Table 13 maximum sizes |
| Any ADU on a T3-R lot | Not permitted | Miami 21 Table 3: ADU blank in T3-R |
| ADU larger than 10 percent of the lot or the cap | Not approvable; no Waiver of maximum size | Miami 21 Table 13 |
| Renting the ADU | Permit, certificate of occupancy ($105) and $300 registration, $250 yearly | City Code 2-214; homestead required |
| Legalizing an existing unpermitted ADU | Amnesty program: $250 pre-submittal meeting, double-fee penalty waived | City Code 10-77 |
| ADU on a lot with a duplex or no homestead | Not eligible as of right / cannot be rented | Miami 21 3.18; City Code 2-214 |
How Much Does an ADU Permit Cost in Miami?
Permit fees are the smaller half. The master building permit is charged 0.50 of the estimated construction cost, read as one-half of one percent (the commercial rate in the same section is one percent), with a $110 minimum; each electrical, plumbing and mechanical trade permit is charged the same way on its own scope with its own $110 minimum. Every permit adds a $40 application fee and state surcharges of 1 percent and 1.5 percent of its fee; the master permit also pays the solid waste surcharge of $0.22 per $100 (capped at $600) and the energy conservation surcharge of $0.11 per square foot of new construction. A residential certificate of occupancy is $105 per unit, and a Miami-Dade County code-compliance surcharge of unstated rate applies.
Worked example, a $150,000 detached 600 square foot ADU: building permit $750 + $40 + solid waste $330 + energy $66 + state surcharges $18.75 = $1,204.75; three trade permits at $110 + $40 + $4 = $154 each; CO $105; permits total about $1,771.75. A $250,000 two-story 800 square foot unit: building permit $1,250 + $40 + $550 + $88 + $31.25 = $1,959.25, plus the same trades and CO, about $2,526.25.
City Code Chapter 13 charges impact fees on every new dwelling unit; the single-family detached row is $164 police, $704 fire-rescue, $413 general services and $6,818 parks, $8,099 together, and the Zoning department decides which land-use row an ADU falls in. Miami-Dade County separately collects road and school impact fees countywide (the city collects its own fire fee), at rates not stated in any city document. That is why a detached ADU lands at $10,000 and up once impact fees are included.
Who Builds It and What Comes After?
Contractors need a Florida license or a Miami-Dade County certificate of competency; an owner-occupant may file as owner-builder under Florida Statute 489.103(7). After the CO, renting requires a notarized ADU owner disclosure statement, proof of homestead and an ADU registration certificate at $300 for the first inspection and $250 each year, with $75 re-inspections; operating an unregistered rental ADU doubles those fees. Existing unpermitted units can enter the ADU amnesty program, which waives the double-fee penalty for a $250 pre-submittal meeting.
How to Get a ADU Permit in Miami
Confirm the transect zone and lot math
Check that the lot is T3-L, T3-O or T4-T6 with a single-family house, then size the unit at no more than 10 percent of the lot area and the 800 or 500 square foot cap.
Design to Miami 21 3.18
Ancillary setbacks, height under the house, separate entrance away from the street, clerestory windows on abutting upper walls, and one parking space unless in a TOD.
File the master permit with three trade permits
Each carries a $40 application fee; the up-front fee of $2.80 per $1,000 of value is 80 percent credited later. Submit the notarized ADU owner disclosure statement if you plan to rent.
Pay permit fees and impact fees before issuance
Building permit at 0.5 percent of cost plus surcharges and the energy surcharge, the trade permits, and the city and county impact fees the Zoning department assesses.
Inspect, obtain the CO, then register
After the $105 certificate of occupancy, register the ADU with the Office of Zoning ($300, then $250 a year with an inspection) before renting; homestead proof is required.