ADU Rules in Mandan, North Dakota

Mandan is the county seat of Morton County and sits on the west bank of the Missouri River, directly across from Bismarck. Although Mandan and Bismarck together form the Bismarck-Mandan metropolitan area and are connected by several river crossings, Mandan is a completely independent city. It has its own government, its own zoning ordinance, and its own planning department. This page covers Mandan only — for Bismarck, see the separate Bismarck ADU rules page.

The Heart River joins the Missouri River near Mandan, creating additional river corridor considerations for development in the area. Mandan has a distinct community character and a history tied to the Lewis and Clark Expedition, which wintered nearby at Fort Mandan in 1804–1805.

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 Mandan are established exclusively by the City of Mandan Zoning Ordinance. There is no state mandate requiring Mandan to allow ADUs or limiting the city's authority to regulate them.

ADU Types Potentially Allowed

Mandan's zoning code may permit various ADU configurations in residential districts:

• Detached ADUs — a standalone accessory structure in the rear yard or elsewhere on the lot
• Attached ADUs — living space added to the primary home sharing at least one wall
• Garage conversions — converting an existing attached or detached garage to a residential unit
• Basement/interior ADUs — a self-contained unit created within the existing structure's interior space

Allowances vary by zoning district. Contact the Mandan Planning and Zoning Department to confirm which ADU types are permitted for your parcel's specific zone designation.

Typical Development Standards

ADUs in Mandan are generally subject to standards such as:

• Minimum lot size — a threshold lot area is typically required before an ADU is permitted
• Maximum ADU size — typically capped as a percentage of the primary dwelling's gross floor area or an absolute maximum (commonly 800–1,000 sq ft)
• Setbacks — rear and side yard setbacks apply; detached ADUs in rear yards commonly require at least 5 feet from property lines
• Height limits — detached ADUs generally limited to one story or the accessory structure height limit for the applicable zone
• Parking — one additional off-street parking space is often required for ADU occupants
• Utility connections — proper water, sewer, and electrical connections required per city codes

All specific standards should be verified directly with the Mandan Planning and Zoning Department, as the code may differ from Bismarck's and from general state patterns.

Missouri River and Heart River Flood Zones

Mandan sits at the confluence of the Missouri River and the Heart River, both of which have FEMA-mapped flood zones. Properties near either river may fall within a Special Flood Hazard Area (SFHA). ADU construction in a flood zone requires:

• A floodplain development permit in addition to standard building permits
• Finished floor elevations at or above the Base Flood Elevation (BFE)
• Compliance with Mandan's floodplain management ordinance

Flood zone designations can change over time as FEMA updates its Flood Insurance Rate Maps (FIRMs). Always verify your parcel's current flood zone status with the City Engineer's office or the FEMA Flood Map Service Center before designing an ADU.

Extreme Climate Requirements

Mandan shares the harsh continental climate of central North Dakota, with winter temperatures regularly falling to −20°F or lower. All construction must comply with North Dakota building codes requiring:

• Foundation depth: Footings must extend well below the frost line (42–60 inches)
• Insulation: High-performance wall, roof, and foundation insulation
• Heating systems: Mechanical systems sized for extreme cold weather conditions

Permit Process

1. Confirm your property's zoning district and ADU eligibility with the Mandan Planning and Zoning Department
2. Verify flood zone status for your parcel (Missouri River and Heart River floodplains)
3. Obtain any required zoning approvals or conditional use permits
4. Submit a building permit application with complete construction drawings
5. Complete all required inspections throughout construction

Contact Information

City of Mandan Planning and Zoning Department

• Website: cityofmandan.com/departments/planning_zoning
• Address: City Hall, 205 2nd Street NW, Mandan, ND 58554
• Phone: (701) 667-3212

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 Mandan Planning and Zoning Department and consult a licensed architect or contractor before beginning any project.