Accessory dwelling units — Sebastian, Florida

Yes: since Ordinance O-25-06 of April 9, 2025, the City of Sebastian allows one accessory dwelling unit per tax parcel alongside a single-family home, but never as a short-term vacation rental.

An accessory dwelling unit, or ADU, is an ancillary or secondary living unit with a separate kitchen, bathroom and sleeping area, inside the same structure as the main home or on the same lot, in the definition used by Florida Statutes 163.31771. Sebastian added the rules as Section 54-2-7.23 of its Land Development Code, and the Municode history note dates that section to Ord. No. O-25-06, April 9, 2025 (Sebastian LDC 54-2-7.23). The section applies to existing single-family residences and to zoning districts where single-family homes are a permitted use.

The 2025 ordinance also closed out the older guest house route. The city ordinance list summarizes O-25-06 as deleting guest houses as conditional uses from the RE-40 and RS-20 zoning districts and deleting the conditional use criteria in Section 54-2-6.4 (City of Sebastian 2025 Ordinances). In practice, a backyard cottage, a garage apartment or an in-law suite in Sebastian is now permitted as an ADU under one set of standards rather than as a guest house heard as a conditional use.

The code states five purposes for Sebastian ADUs: a diverse housing supply, flexible and affordable living accommodations, letting homeowners use excess space to offset the cost of home ownership, room for multigenerational living and aging in place, and repurposing existing structures and developed lots instead of sprawl (Sebastian LDC 54-2-7.23). Aging in place matters in a city where the U.S. Census Bureau puts the median age at 58.2 in its 2020 to 2024 American Community Survey estimate (Census ACS table B01002, Sebastian city).

A Sebastian ADU may cover no more than half of the main house's air-conditioned floor area or 1,000 gross square feet, whichever is less, and no less than 300 gross square feet.

The size cap is measured against the principal dwelling. A 1,600 square foot house under air in Sebastian could carry an ADU of up to 800 square feet (half of 1,600); a 2,400 square foot house reaches the 1,000 square foot ceiling. The gross floor area of the ADU shall not exceed 50 percent of the principal dwelling or 1,000 gross square feet, whichever is less (Sebastian LDC 54-2-7.23).

Height is limited for detached units. A detached ADU in Sebastian shall not exceed one story in height, although the unit may sit on a second story when the first story is used as a garage or storage (Sebastian LDC 54-2-7.23). Otherwise the ADU must meet the setback and lot coverage rules of the district the property lies in.

Rear yards get one exception. Under the accessory structures section, detached structures such as sheds and ADUs in a Sebastian residential district may encroach into a required rear yard, provided they keep a minimum distance of ten feet from the rear property line and stay out of any dedicated easement (Sebastian LDC 54-2-7.5). Two caps that bind sheds and workshops do not bind ADUs: the allowance of five square feet of accessory building area per 100 square feet of lot area, up to 1,000 square feet, excludes ADUs, and so does the planning staff review of accessory buildings over 500 square feet.

For comparison, the RS-10 single-family district, which the Sebastian code describes as low-density development on lots of 10,000 square feet, sets a 9,500 square foot minimum lot size, front setbacks of 25 feet, side setbacks of 10 feet, rear setbacks of 20 feet, 30 percent maximum building coverage and a 1,200 square foot minimum living area for the main house (Sebastian LDC 54-2-5.2.3).

A Sebastian ADU can be lived in or rented long term, but the code bars transient short-term rental, condominium conversion and any ownership separate from the main house.

Three uses are prohibited outright in Section 54-2-7.23(b). The first is leasing the ADU for transient short-term rentals as defined in Section 54-2-7.22(1)(a), the Sebastian vacation rental section, which covers dwellings rented more than three times a calendar year for less than 30 days. The second is converting the ADU into a condominium or any other form of legal ownership distinct from the house. The third is turning the ADU into a primary dwelling, unless it becomes the only dwelling on the lot and meets the district rules for a primary home (Sebastian LDC 54-2-7.23).

Commercial use is also out, with one exception: a home business that has been permitted and complies with the Sebastian home business rules in Section 54-2-7.21. No ADU may be established in conjunction with a multi-family dwelling unit.

Long-term renting comes with a state-law condition. A Sebastian building permit application for an ADU must include an affidavit from the applicant attesting that the unit will be rented at an affordable rate to an extremely-low-income, very-low-income, low-income or moderate-income person, as defined by Florida Statute 163.31771 (Sebastian LDC 54-2-7.23). The statute defines an affordable rental as one where monthly rent and utilities do not exceed 30 percent of the income level for those groups (Florida Statutes 163.31771). The same statute says each ADU allowed under such an ordinance counts toward the affordable housing component of the local comprehensive plan housing element, which is how Sebastian ADUs feed into the city's housing planning.

A Sebastian ADU must share one tax parcel and one street address with the main house, sit on a lot that meets the district minimum or is legally platted, and use city or county utilities where available.

Ownership is kept together on paper. The ADU and the principal dwelling must sit on a single lot or on lots unified under a recorded unity of title and combined into one tax parcel, and the ADU uses the same address as the main structure (Sebastian LDC 54-2-7.23). The Sebastian Community Development Department lists Unity of Title among the development activities it coordinates, along with variances and zoning interpretations (City of Sebastian Community Development).

Density does not block an ADU. A single-family lot proposing one is exempt from the maximum gross residential density set by the Sebastian Future Land Use Map for that parcel. The ADU must be clearly incidental to the house and can only be built with or after the principal dwelling, so an empty Sebastian lot cannot start with the small unit first. Private covenants still govern: the code says its ADU requirements do not supersede property owner or subdivision deed restrictions (Sebastian LDC 54-2-7.23).

Utilities follow what the street has. An ADU in Sebastian is served by centralized water and wastewater if available; otherwise it must meet the health department well and septic requirements, and any new or expanded septic system or well may not make an adjacent vacant lot unbuildable. Adequate on-site parking is required for both the house and the ADU, and the unit is charged an impact fee in the residential category set by Indian River County (Sebastian LDC 54-2-7.23).

Design rules keep the unit residential. The facade and materials of a detached Sebastian ADU must be similar to the main house, with conventional residential windows and doors, and mobile homes or recreational vehicles shall not be used as ADUs; the unit must meet Florida Building Code minimums for a dwelling.

A Sebastian ADU is permitted like other residential construction, through the Building Department at Sebastian City Hall, 1225 Main Street, using the MGO Connect online portal.

The code allows four ways to create the unit: converting existing living area, attic or garage; adding floor area to the house or garage; building a detached ADU on a lot with an existing house; or building a new house with an internal or detached ADU (Sebastian LDC 54-2-7.23). The affidavit on affordable rent goes in with the building permit application.

The Building Department runs online permitting through MyGovernmentOnline, where applicants apply for permits, upload documents, make payments and schedule inspections; inspections need to be scheduled one day in advance (City of Sebastian Building Department). The department phone is 772-589-5537 and its hours are Monday through Friday 8 am to 4:30 pm, closed noon to 1 pm. Owner/builder permits can use the portal, but the initial application has to be made in person at the Building Department at 1225 Main St. in Sebastian (City of Sebastian Online Permits).

Zoning questions such as setbacks, the RS-10 or RS-20 district standards, or a unity of title go to the Community Development Department in the same building, phone 772-589-5330 (City of Sebastian Community Development).

Last verified: October 11, 2026, on the City of Sebastian website.