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How big a backyard home (accessory dwelling unit) can be in Monroe County, who can build one, and who to call to confirm — from the county's published rules.
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| ADUs allowed? | Yes, with conditions |
|---|---|
| Maximum ADU size | 800 sq ft or 40% of the main home, whichever is less |
| Minimum lot size | 3,000 sq ft |
| Owner must live on site? | Not confirmed in our records |
| Manufactured home as an ADU? | Often allowed, subject to the county's ADU and zoning rules |
SPECIAL CASE — the Florida Keys. New dwelling units (incl. ADUs) require a permit allocation under the competitive ROGO/NROGO Rate-of-Growth system, which is severely capped, plus a tier-based environmental score. An ADU needs a min 3,000 sq ft lot and is capped at 800 sq ft / 40% of the principal structure, max 2 bedrooms. NOTE: affordable/replacement units must meet current Florida Building Code and CANNOT be a mobile home. Also HVHZ + coastal flood construction. Islamorada, Key West, Marathon, Layton self-govern. Expect long waits and heavy restrictions.
Source: Monroe County LDC Ch. 138 (ROGO) + Sec. 22.16.050; verified Jul 2026.
Before You Build
ADU rules are set by each county and city — Florida law (Fla. Stat. 163.31771) lets local governments allow ADUs but doesn't require it — and they can change, so always confirm the current rule with Monroe County before you build.
Confirm with Monroe County: 305-289-2500 · zoning department website ↗
Zoning is set locally and changes often. Answers are guidance only, not a permit guarantee. Always confirm with the local building/zoning department before purchase.
Common Questions
Yes, with conditions. SPECIAL CASE — the Florida Keys. New dwelling units (incl. ADUs) require a permit allocation under the competitive ROGO/NROGO Rate-of-Growth system, which is severely capped, plus a tier-based environmental score. An ADU needs a min 3,000 sq ft lot and is capped at 800 sq ft / 40% of the principal structure, max 2 bedrooms. NOTE: affordable/replacement units must meet current Florida Building Code and CANNOT be a mobile home. Also HVHZ + coastal flood construction. Islamorada, Key West, Marathon, Layton self-govern. Expect long waits and heavy restrictions.
800 sq ft or 40% of the main home, whichever is less.
Our records don't confirm an owner-occupancy requirement for Monroe County — ask the county zoning department before you buy.
Often yes — many Florida counties allow a manufactured or modular home as an accessory dwelling unit, subject to Monroe County's ADU size, lot, and setback rules. Confirm with the county for your parcel.
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