What is a backyard ADU?
It is a complete, separate dwelling on your lot: a bedroom or two, a bathroom, a kitchen and its own front door. In Jacksonville it is the type that gives a tenant or relative the most privacy, and it lets us set the floor height from scratch, which matters on a low lot.
How large can it be in Jacksonville?
As reported when the City Council passed Ordinance 2022-0448 in November 2022, the ADU's footprint is limited to 25% of the main home's gross floor area or 750 sq ft, whichever is less. On a 2,000 sq ft house, that works out to a 500 sq ft footprint. A bigger main house raises the cap until it reaches 750 sq ft.
Where on the lot does it go?
- Behind the main house, with a visual relationship to it.
- No taller than the main house.
- Outside the setbacks for your zoning district; we confirm the exact distances with the Zoning Section for each lot.
- Clear of easements, drainage swales and septic fields.
How does flood zone affect a detached ADU?
On a lot in a FEMA special flood hazard area, the lowest floor of new living space has to sit at or above the elevation the floodplain rules require. That can mean stem walls, a raised slab or piers. Because a detached ADU is new construction, we can design for that from the start. See flood and wind rules for Jacksonville ADUs.
What about hurricane design?
Every new ADU follows the Florida Building Code's wind provisions for its location: engineered roof-to-wall and wall-to-foundation connections, approved windows and doors, and opening protection where the site is in a wind-borne debris region. The 9th edition of the code takes effect December 31, 2026.
When is a backyard ADU the wrong choice?
It depends on the yard. A shallow lot, a septic drain field across the back, or a big live oak can leave no legal footprint. In those cases an in-law suite or a garage apartment may fit where a cottage cannot.
Related
As of October 2026. Sources: Jacksonville Daily Record on Ordinance 2022-0448; ICC on the 2026 Florida Building Code; FEMA floodplain basics. Confirm your lot with the City of Jacksonville.