ADU Rules in Bismarck, North Dakota

Bismarck is North Dakota's capital city and the county seat of Burleigh County, located on the east bank of the Missouri River. The city anchors the Bismarck-Mandan metropolitan area along with the separately governed City of Mandan, which sits across the Missouri River in Morton County. Despite sharing a metro area, Bismarck and Mandan are completely independent cities with separate zoning codes — this page covers Bismarck only.

No Statewide ADU Law — Local Zoning Controls

North Dakota has not passed statewide legislation preempting or standardizing local ADU regulations. All rules governing Accessory Dwelling Units (ADUs) in Bismarck are set exclusively by the City of Bismarck Zoning Ordinance. There is no state mandate requiring Bismarck to permit ADUs or restricting the city's ability to regulate them.

ADU Types Potentially Allowed

Bismarck's zoning code may allow various ADU configurations depending on the residential district:

• Detached ADUs — freestanding structures in the rear yard, such as a carriage house or backyard cottage
• Attached ADUs — additions to the primary home sharing at least one wall
• Garage conversions — converting an existing attached or detached garage into a habitable living unit
• Basement/interior ADUs — a self-contained unit created within existing interior space

Allowances differ by zoning district. Single-family residential zones typically have more restrictions than mixed-residential zones. Consult the Bismarck Zoning Ordinance or contact the Planning and Zoning Division to determine what applies to your specific parcel.

Typical Development Standards

ADUs in Bismarck are generally subject to standards such as:

• Minimum lot size — a threshold lot area is typically required before an ADU is allowed
• Maximum ADU size — typically limited as a percentage of the main dwelling's gross floor area or an absolute cap (often 800–1,000 sq ft)
• Setbacks — rear and side yard setback requirements apply; detached rear-yard ADUs are often required to be at least 5 feet from rear and side property lines
• Height — detached ADUs are usually capped at one story or a height limit consistent with accessory structures in the zone
• Parking — additional off-street parking space(s) may be required for the ADU occupants
• Utility connections — ADUs must have separate or shared utility metering in compliance with city codes

All specific dimensions and thresholds should be verified directly with the Bismarck Planning and Zoning Division.

Missouri River Flood Zone Considerations

The Missouri River forms Bismarck's western boundary, and FEMA-mapped flood zones exist along the river corridor. Properties in a Special Flood Hazard Area (SFHA) may be subject to additional requirements for any new construction, including ADUs:

• Finished floor elevations must meet or exceed the Base Flood Elevation (BFE)
• A floodplain development permit may be required in addition to a standard building permit
• Fill, grading, and foundation requirements may be more stringent in flood zones

Verify your parcel's flood zone status using the FEMA Flood Map Service Center or by contacting the City Engineer's office before designing an ADU.

Extreme Climate Requirements

Bismarck experiences harsh continental winters with temperatures regularly reaching −20°F to −30°F. All ADU construction must comply with North Dakota building codes addressing:

• Frost depth: foundations must extend well below the frost line (typically 42–60 inches in this region)
• Thermal envelope: high-performance insulation required for walls, roofs, and foundations
• Mechanical systems: heating systems must be appropriately sized and redundant systems are advisable

Permit Process

To build or convert an ADU in Bismarck:

1. Confirm the property's zoning district and ADU eligibility with the Planning and Zoning Division
2. Obtain any required zoning approvals or conditional use permits
3. Submit a building permit application with complete construction drawings
4. Schedule required inspections throughout construction (foundation, framing, rough mechanical, final)

Contact Information

City of Bismarck Planning and Zoning Division

• Website: bismarcknd.gov/195/Planning-Zoning
• Address: Municipal Center, 221 North 5th Street, Bismarck, ND 58501
• Phone: (701) 355-1840

Disclaimer: Zoning regulations change frequently. The information on this page is provided for general informational purposes only and may not reflect the most current rules. Always verify ADU requirements directly with the City of Bismarck Planning and Zoning Division and consult a licensed architect or contractor before beginning any project.