St. Petersburg permits accessory dwelling units (ADUs) in the NS-1 and NS-2 Neighborhood Suburban single-family districts (a permitted use in the Use Permissions Matrix, LDR Sec. 16.10.020.1), and the ADU may be in a detached structure. The controlling standards are LDR Sec. 16.50.010, as amended by Ordinance 611-H (July 10, 2025); the city's 2022 ADU handout predates that amendment. unverified
Size. Gross floor area may not exceed 800 square feet, and all areas under roof may not exceed 67 percent of the floor area of the principal dwelling, whichever is more restrictive. For a detached ADU the limit applies to the combined ADU plus any accessory living space in the same building, excluding up to 300 square feet per required enclosed parking space (maximum three).
Lot standards (all NS districts). The lot must meet one of: (a) at least 10,000 square feet of lot area; (b) on an alley with at least 4,500 square feet; or (c) a corner lot meeting the district minimum lot area and width (NS-1 residential minimums: 5,800 square feet and 75 feet of width, Sec. 16.20.020.6). One ADU per single-family dwelling, only after the principal building exists, and no transient (short-term) use. unverified
Placement. A detached ADU is allowed only if the legal front and rear of the lot match the front and rear yards of the block face. Side setback: 10 feet minimum, reduced to 7.5 feet on an alley lot. Rear yard for accessory buildings in NS-1: 10 feet where the roofline begins at 24 feet or less. Height: accessory buildings max 20 feet to the beginning of the roofline and 30 feet to the roof peak.
Parking. One space for units up to 2 bedrooms (plus 0.5 per additional bedroom); at least one space must be unobstructed and exclusive to the ADU. The requirement is waived only if ALL of: within 660 feet of a high-frequency transit route, unit 600 square feet or less, on an alley, all house parking accessed from the alley, and no front-loading driveway.
What is NOT required. Owner-occupancy or homestead of either unit is not required. If both units are rentals, a Business Tax Certificate is required.