Building an ADU in Miami

What changed in 2025

Florida leaves ADUs to cities (see our Florida ADU law page). Before 2025, Miami's ordinance says, "ADUs are only allowed in T3-L and T4." On June 17, 2025, the City Commission adopted Ordinance 14375 "with modification(s)," which took effect ten days after adoption. It added Section 3.18, "Ancillary Dwelling Unit (ADU) Standards," to the Miami 21 Code and renamed outbuildings "Ancillary Buildings."

The Planning Department's staff report proposed widening ADUs "from T3-L to all T3 Lots that contain a single-family home" and to lots with a single-family home in T4, T5, T6, CI-HD and D1. Before the vote, a substitution memo removed T3-R "from the proposed allowable locations for ADUs" and added the 500-square-foot cap for internal and attached ADUs. Confirm your zone with the Office of Zoning.

These rules are for the City of Miami. Unincorporated Miami-Dade County and other cities in the county have their own codes. [1][2][3][5][6]

What counts as an ADU

Miami 21 defines an ADU as "A secondary Dwelling Unit that shares ownership and utility connections with a Principal Building and contained on the same Lot." It has its own sleeping or living area, shower or bathroom, and a kitchen with a sink, food-prep countertop and refrigerator, all separate from the main home. An ADU does not count toward the zone's maximum density.

An ADU may be inside the main house or in an ancillary building, attached or detached. Accessory structures such as sheds and summer kitchens can only hold non-habitable uses. [2]

Size, height and placement

Size (Article 6, Table 13). Minimums: 275 square feet for an efficiency, 450 for one bedroom, 550 for two bedrooms. Maximums: a detached ADU can be "ten (10) percent of the Lot Area, up to 800 square feet," and an ADU within or attached to the house ten percent of the lot area, up to 500 square feet. "No Waivers shall be applied to maximum unit size."

Height. "Ancillary Buildings shall be limited to two (2) Stories," with one story in T3-R, and "shall be no taller than the Principal Building."

Placement. A one-story ancillary building may be attached or detached and follows the setbacks for ancillary buildings. A two-story detached ancillary building must be at least 10 feet from the house and follow ancillary building setbacks; a two-story attached one follows the main building's setbacks. Setback distances vary by zone, so ask the Office of Zoning for yours. [2]

Design rules

Section 3.18 requires:

• a separate entrance from the main unit;
• if the ADU is in the main house, the building must look like one single-family home and the ADU entrance "shall not face the street";
• an ancillary building "visually harmonious with the architecture of the Principal Building";
• on a second story facing an abutting property, only clerestory windows no more than 24 inches tall.

Awnings, canopies or an outdoor area are encouraged. [2]

Parking

In T4 zones, Miami 21 Table 4 requires "Minimum of 1 parking space per Ancillary Dwelling Unit," and "Within a TOD or Transit Corridor no parking is required." Ask the Office of Zoning for the requirement in your zone.

If an existing legal house keeps the ADU's space from fitting in the second or third layer of the lot, Section 3.18 lets it go in the first layer (the front), exempts it from driveway separation and some paving rules, and requires parking strips. [2]

Renting your ADU: homestead and registration

Section 3.18 says the house and ADU "shall be under the same ownership," and "An ADU may only be rented if the property has current proof of Homestead status." Homestead means the property is the owner's primary residence and qualifies for Florida's homestead exemption.

City Code Section 2-214 (adopted July 10, 2025) sets the registration process. To rent, you need an approved building permit with a notarized "ADU owner disclosure statement," a certificate of occupancy, and an "ADU registration certificate." Registration includes an inspection and is renewed every year. Fees are $300 for initial registration and inspection, $250 for annual renewal and $75 per re-inspection. Operating without a certificate means double fees and a zoning violation. If homestead status changes, you must tell the Office of Zoning within 30 days.

ADUs "shall only be used as predominately permanent housing," and renting one "as transient or temporary lodging" is a reason to deny or revoke the certificate. A denial or revocation can be appealed within 15 days. Florida law separately limits local vacation-rental rules adopted after June 1, 2011 (see our Florida ADU law page); ask the Office of Zoning if you have questions about short stays. [2][4][7]

Legalizing an existing unpermitted ADU

Section 10-77 created an ADU amnesty program for properties with existing violations, and for owners who come forward on their own. You can book an optional pre-submittal meeting with the Office of Zoning ($250) to review whether the unit can be legalized; approval "is not guaranteed." Participants then follow the Section 2-214 registration steps, and the city waives the "double permit fee plus fine" for the unpermitted work. [4][8]

Fees, flood zones and building code

The staff report says ADUs "are subject to Impact Fees" and that adding one "may impact the value or homestead status of a property." Ask the building department for your permit and impact fee estimate, and see our ADU cost guide.

ADUs must meet the Florida Building Code. Plans submitted on or after December 31, 2026 must follow its 9th (2026) edition. If you are in a flood zone, FEMA treats improvements costing 50% or more of a building's market value as a substantial improvement; check FEMA's Flood Map Service Center. [2][5][9][10]

Permit steps in Miami

1. Find your transect zone

   Look up your property's Miami 21 zone with the city's zoning category lookup. ADUs are allowed only on lots with a single-family home in zones that list them in Table 3, and not in T3-R. [2][3][11]

2. Ask the Office of Zoning about your lot

   Call 305-416-1495 or email miamizoning@miamigov.com. All zoning functions close to the public at 2:30 p.m. Ask about setbacks, size and parking for your zone. [11]

3. Design to Section 3.18

   Put the ADU inside the house or in an ancillary building, with its own entrance. Keep the ancillary building no taller than the house, and use only clerestory windows (24 inches tall or less) on a second story facing a neighbor. [2]

4. Apply for the building permit

   Apply through the city's electronic plan review (ePlan); see All Things ePlan. If you plan to rent, submit a notarized ADU owner disclosure statement to the Office of Zoning with the building permit. [4][11]

5. Get a Certificate of Occupancy

   An approved certificate of occupancy (CO) is required before you can register the ADU for rent. [4]

6. Register before renting, and renew every year

   Register with the Office of Zoning for an ADU registration certificate, show proof of homestead exemption, and pass a virtual or in-person inspection. Renew annually with a new inspection and homestead proof. [4]

Who to call

• City of Miami Office of Zoning

  Miami 21 zoning questions, ADU owner disclosure statements and ADU registration (miamizoning@miamigov.com)

  305-416-1495

  Miami Riverside Center, 444 SW 2nd Avenue, 2nd Floor, Miami, FL 33130

  [11]

Questions people ask