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How big a backyard home (accessory dwelling unit) can be in Nassau County, who can build one, and who to call to confirm — from the county's published rules.
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| ADUs allowed? | Yes |
|---|---|
| Maximum ADU size | 800 sq ft or 50% of the main home, whichever is less |
| Owner must live on site? | Yes — in the main home or the ADU |
| Manufactured home as an ADU? | Often allowed, subject to the county's ADU and zoning rules |
Allowed BY RIGHT in all residential districts that permit single-family homes. One per parcel. Max height 25 ft; detached units min 6 ft setback. If the ADU is rented, the main home must be the owner's primary residence with an active homestead exemption. Fernandina Beach (Amelia Island) has its own rules.
Source: Nassau County LDC Sec. 28.15; 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 Nassau County before you build.
Confirm with Nassau County: 904-530-6300 · 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. Allowed BY RIGHT in all residential districts that permit single-family homes. One per parcel. Max height 25 ft; detached units min 6 ft setback. If the ADU is rented, the main home must be the owner's primary residence with an active homestead exemption. Fernandina Beach (Amelia Island) has its own rules.
800 sq ft or 50% of the main home, whichever is less.
Yes. Nassau County requires the owner to live on the property, in either the main home or the ADU.
Often yes — many Florida counties allow a manufactured or modular home as an accessory dwelling unit, subject to Nassau County's ADU size, lot, and setback rules. Confirm with the county for your parcel.
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