Harrison County, MS Accessory Structures: ADU Rules (2026)

Harrison County handles accessory dwelling units through local zoning ordinances under MS Code Ann. §17-1-1 et seq. Mississippi has no statewide ADU legislation similar to California's SB 9/SB 10 or Oregon's HB 2001, so all regulation is local. Some Harrison County municipalities permit ADUs in certain residential zones through conditional use permits (CUPs), while others prohibit them outright in single-family zones. Common requirements include: maximum size limits (typically 600-1,000 square feet or 40-50% of the primary dwelling), owner-occupancy of either the primary or accessory unit, separate utility connections (or legal sub-metering), off-street parking (usually 1-2 additional spaces), compliance with setback and lot coverage rules, and standard building code compliance. FEMA flood zone elevation requirements add major cost in coastal Harrison County: any new habitable space in AE/VE zones must be elevated above Base Flood Elevation (BFE), often 12-17 feet. This makes traditional backyard cottage ADUs impractical in many beachfront areas; above-garage ADUs are more common. Post-Katrina housing pressure and growing workforce housing demand is driving Biloxi and Gulfport to consider more ADU-friendly policies. Manufactured housing and mobile homes used as ADUs face additional restrictions. HOAs in developments like Diamondhead and Grand Bayou typically prohibit ADUs entirely.