Martin County, FL Accessory Structures: ADU Rules (2026)
ADU rules in Martin County, FL, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Countywide Rule
- Nonresidential developments only (LDR 3.51)
- Countywide Cap
- Three ADUs per lot maximum
- CRA Rule
- One ADU per single-family lot
- CRA Size Limit
- 850 sq ft or half primary
- Sale
- Cannot be conveyed separately
Summary
Martin County treats accessory dwelling units two ways. Countywide, LDR 3.51 allows them only as part of a nonresidential development, capped at three per lot. Inside a designated Community Redevelopment Area, LDR 12.1.04.7.a allows one ADU on a single-family or townhouse lot.
Housing; Authorizing a landlord to accept reusable tenant screening reports and require a specified statement; requiring, rather than authorizing, local governments to adopt, by a specified date, an ordinance to allow accessory dwelling units in certain areas; authorizing a local government to provide a density bonus incentive to landowners who make certain real property donations to assist in the provision of affordable housing for military families; requiring the Office of Program Policy Analysis and Government Accountability to evaluate the efficacy of using mezzanine finance and the potential of tiny homes for specified purposes, etc.
Full Breakdown
Under LDR 3.51.A, accessory dwelling units shall be established only as part of a nonresidential development such as a marina, residential storage facility or manufacturing use, and 3.51.B caps them at three on a single lot. The Community Redevelopment Code sets a different rule inside the county's six formally designated CRAs: 12.1.04.7.a.i permits one ADU on a lot with a detached single-family dwelling or townhouse, but not on a duplex lot; the ADU may be a second-floor garage unit, a freestanding cottage or attached to the principal dwelling; it may not exceed the lesser of 850 square feet or half the primary dwelling; and it may not be sold separately.
Violations & Fines
Building or occupying an unpermitted dwelling unit is a chapter 21 violation, a second-degree misdemeanor under Sec. 21.12, and the special magistrate may impose fines up to $1,000.00 per day under Sec. 1.97.
Frequently Asked Questions
Can I build an ADU in Martin County?
Can I rent out my ADU?
Sources & Official References
Other rules in Martin County
How Martin County compares: Easiest Cities to Build an ADU·Florida rules heatmap·Compare Martin County to another location·View the Florida accessory structures overview
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