ADU Miami-Dade: Zoning, Permits, and Underwriting in 2026

Last updated: August 2026

An accessory dwelling unit is legal on some Miami-Dade single-family lots and illegal on others. The dividing line is which government has jurisdiction over the parcel. In unincorporated Miami-Dade, Section 33-22 of the county code permits one accessory unit per lot in the AU, EU, and RU zoning districts inside the Urban Development Boundary, plus GU parcels trended to those districts [1]. The county's standards follow its Comprehensive Development Master Plan: a minimum lot area of 7,500 square feet, with habitable area between 400 and 800 square feet in RU-1 [1][2]. A permitted ADU may be rented for a fee provided the rental term is not less than one month, and it may carry electric, water, and gas meters, a house address, and a mailbox separate from the principal dwelling [1]. It may not be sold separately from the principal dwelling, and it may not be used as a standalone vacation rental [1].

If the parcel sits inside a municipality, none of that governs it. City of Miami parcels fall under Miami 21, and every other incorporated city writes its own rules. Florida law does not make accessory units legal statewide: Fla. Stat. 163.31771 authorizes a local government to adopt an ADU ordinance, it does not require one [3]. Verify with your own building and zoning department before you underwrite anything.

What the unincorporated county code actually allows

Section 33-22 caps the property at one accessory unit and draws a hard line between two kinds. An ADU can be rented separately. A guesthouse cannot, and is barred from separate meters, address, or mailbox [1]. If the thesis is rental income, only the ADU designation gets you there.

Dimensional rules track the principal structure. Detached units over one story and all attached units carry the same minimum setbacks and maximum lot coverage as the principal dwelling. Detached single-story units follow accessory-structure setbacks for the district, cannot exceed the height of the principal dwelling, and cannot sit in front of it [1]. Parking is one space beyond what the principal dwelling already requires, in a driveway, designated area, or the swale directly in front where allowed. Parcels within 660 feet of a CDMP-designated major corridor served by transit are exempt from that off-street provision [1].

The operating obligation is a certificate of use, renewable annually and obtainable only by the owner of the principal dwelling. It records unit type, size, attachment, and occupancy, with occupant names updated on turnover [1]. Failure to obtain a CU, or other violation of Section 33-22, carries civil penalties of $500 for a first offense, $1,000 for a second, and $2,500 for each subsequent offense [1].

Municipal codes differ, and that is the underwriting risk

The county ordinance covers unincorporated Miami-Dade only. City of Miami parcels are governed by Miami 21, which handles ancillary units through its transect zones rather than Section 33-22, and the city has been amending which T3 sub-zones qualify. For [Coral Gables](/neighborhoods/coral-gables) and [Pinecrest](/neighborhoods/pinecrest), the governing text, the minimum lot area, and the rentability question are separate determinations. Some municipalities allow a second structure but prohibit renting it separately, which converts the asset from an income unit into owner-use square footage.

Before you write an offer that depends on accessory-unit income, get the jurisdiction in writing. A zoning verification letter is cheap relative to the assumption it protects.

Septic versus sewer is a common hard stop

Adding a full kitchen and bathroom adds plumbing fixture units, and the sanitary capacity review is where many otherwise workable projects die. Miami-Dade's Division of Environmental Resources Management reviews onsite sewage systems under Ordinance 22-83, and conventional septic systems are no longer permitted for new or total replacement installations. Performance-based treatment systems are required instead [4].

On a sewered lot the added load is usually a capacity and connection question. On a septic lot it can trigger a system upgrade costing a large fraction of the unit itself. Price that review before you price the build.

How an appraiser treats a permitted unit versus an unpermitted one

Fannie Mae defines an ADU as additional living area independent of the primary dwelling with facilities for living, sleeping, cooking, and bathroom use on the same parcel. When one exists, the appraisal report must describe it, analyze its effect on value and marketability, and show the improvements are acceptable for the market [5].

Where zoning does not allow the unit, the property can still be eligible, but the conditions are demanding: the lender must confirm the existence will not jeopardize a future insurance claim, the use must conform to the neighborhood and market, the property must be appraised on its current use, the report must state that the use does not comply with zoning, and it must include at least three settled sales showing the non-compliant use is typical [5].

That is why an unpermitted conversion destroys value. You are asking an appraiser to build an evidentiary case, an underwriter to accept insurance risk, and the next buyer's lender to repeat both. Many decline. The unpermitted unit also produces the fact pattern the county code treats as a rebuttable presumption of illegal use: two or more meters or mailboxes, more than one address, or advertising showing more than one dwelling unit, with no valid CU [1].

How lenders count accessory-unit rental income

Fannie Mae allows rental income from an accessory unit on a one-unit principal residence, on purchase and limited cash-out refinance transactions. Qualifying rental income from the ADU is limited to 30 percent of total qualifying income, only one unit's income counts, and it is documented with Form 1007 or Form 1025 showing market rent [6].

Two implications follow. The cap bounds the additional borrowing capacity the unit can support. And the appraiser's market rent opinion, not your pro forma, is the number that reaches the file, so build the model off Form 1007 logic from the start.

Property tax and homestead consequences

An accessory unit adds assessed improvement value, and new construction is generally assessed at just value in the year it is added rather than inheriting the capped assessment on the homestead. Separately, Fla. Stat. 196.061 provides that rental of all or substantially all of a dwelling previously claimed as homestead constitutes abandonment, tied to rental exceeding 30 days per calendar year in two consecutive years [7]. The Property Appraiser cautions owners against jeopardizing the exemption through rental and notes improper exemptions can be recovered with back taxes, interest, and penalties [8]. Renting a detached unit while still occupying the principal dwelling is a different fact pattern, but that is a determination for the Property Appraiser, not for a blog and not for your contractor.

Insurance

Tell the carrier what you built. A detached rented structure changes the exposure, may require a separate other-structures limit, and may push that portion of the policy toward a landlord form. Carriers can deny claims on undisclosed structures, and Fannie Mae makes insurance-claim risk an explicit eligibility condition for a non-conforming unit [5]. Get a firm quote before committing capital.

A hypothetical yield framework

This is a structure, not a forecast. No return is promised or implied.

Start with all-in delivered cost, not construction cost: design, permit and review fees, impact fees, site work, utility connections, and any sanitary system upgrade. Then build annual net operating income for the unit alone:

Market rent supported by a Form 1007 style analysis, not asking rents
Less vacancy and collection allowance
Less utilities you keep paying if the unit is not separately metered
Less the incremental insurance premium quoted, not estimated
Less incremental property tax on the newly assessed improvement value
Less maintenance reserve, CU renewal, and inspection costs

Divide that net figure by all-in delivered cost for an unlevered yield on cost, then compare it to what the same capital earns elsewhere. If you finance the build, run the levered case with a rate pulled live from the Freddie Mac Primary Mortgage Market Survey on the day you model it, and treat any rate printed in an article as a placeholder. Then rerun at a rent 15 percent below base case and a cost 20 percent above it. If it only works in the base case, it is a construction project wearing an investment costume.

To run this against a specific address, start with a [listing valuation](/listing-valuation) or a [buyer consultation](/buyer-consultation).

Frequently asked questions

Is an accessory dwelling unit permitted on any Miami-Dade single-family lot?

No. Section 33-22 applies to unincorporated Miami-Dade and to specified districts inside the Urban Development Boundary [1]. Incorporated municipalities set their own rules, and Fla. Stat. 163.31771 is enabling legislation rather than a statewide mandate [3]. Confirm with the building and zoning department that has authority over the parcel.

Can the accessory unit be metered and rented separately in unincorporated Miami-Dade?

An ADU may have separate electric, water, and gas meters, a separate address or unit number, and a separate mailbox, and may be rented for a fee provided the term is not less than one month. A guesthouse may do none of those. Neither may be sold apart from the principal dwelling or used as a standalone vacation rental [1].

How much accessory-unit rent will a lender let me use to qualify?

On a one-unit principal residence, Fannie Mae limits qualifying rental income from the accessory unit to 30 percent of total qualifying income, counts only one unit, and requires Form 1007 or Form 1025 support [6]. Other loan programs set their own rules, so confirm with the specific lender.

What happens if the existing unit was never permitted?

The appraisal must state that the use does not comply with zoning, the lender must confirm it will not jeopardize a future insurance claim, and the report must include at least three settled sales showing the non-compliant use is typical [5]. Expect fewer eligible buyers and a longer marketing period, plus county exposure under the Section 33-22 penalty schedule [1].

Gabriel

Sources

Gabriel A. Moyers, PA. eXp Realty. Florida License #3407280. Equal Housing Opportunity. This article is general information as of August 2026 and is not legal, tax, or financial advice. Verify current figures against authoritative sources before acting.