ADU Rules in Frederick, Maryland

Frederick is the Frederick County seat and one of Maryland's largest cities, with a population of about 78,000 in western Maryland approximately 50 miles northwest of Washington DC. As an incorporated city, Frederick has its own Zoning Ordinance separate from Frederick County's regulations. Frederick has a beautifully preserved 18th and 19th-century downtown with significant Civil War history (including the 1864 Battle of Monocacy). The city has been growing rapidly as a DC and Baltimore bedroom community.

Frederick vs. Frederick County

• City of Frederick: Incorporated city with own Zoning Ordinance — use the city's permit process
• Frederick County: Separate county government for unincorporated areas outside the city
• Verify which jurisdiction your property falls in

City of Frederick Zoning Ordinance

The City of Frederick Zoning Ordinance governs all land use within the city limits.

Maryland ADU Rules

ADU rules in Maryland are set by each county and municipality. Verify current ADU requirements with the City of Frederick Planning Department.

Permitted ADU Types

Per Frederick Zoning Ordinance (verify current standards):

• Accessory apartments: Within or attached to primary structure
• Detached ADUs: In eligible residential zones
• Carriage house conversions: In historic contexts

Verify current provisions with Frederick's Department of Planning and Permitting.

Size Limits

Per Frederick Zoning Ordinance:

• Maximum floor area per zone
• Lot coverage restrictions

Setbacks

Per Frederick residential zone:

• Rear: Minimum setback
• Side: Minimum setback

Historic Districts

Frederick has a nationally significant historic downtown. Properties in the Historic District require review by the Frederick Historic Preservation Commission before exterior modifications.

Monocacy River Flood Zones

Parts of Frederick near the Monocacy River and Carroll Creek may be in FEMA flood zones. Carroll Creek has undergone flood control improvements in the downtown area — verify flood zone status.

Chesapeake Bay Watershed

Frederick is in the Chesapeake Bay watershed (Monocacy River drainage). Stormwater management requirements apply.

Permit Process

1. Verify jurisdiction: Confirm your property is within Frederick city limits (not unincorporated Frederick County)
2. Verify zoning: Frederick Department of Planning and Permitting
3. Historic Preservation review: If in the Historic District
4. Check flood zone status: If near the Monocacy River or Carroll Creek
5. Submit plans: Frederick Permit Center
6. Building permit and inspections
7. CO: Required before occupancy

Contact

City of Frederick Department of Planning and Permitting 140 West Patrick Street, Frederick, MD 21701 Phone: (301) 600-3807 Website: cityoffrederickmd.gov

Disclaimer: Frederick City and Frederick County are separate jurisdictions. Historic district review applies to exterior modifications. ADU rules are evolving following Maryland's 2024 statewide legislation. Verify current standards with the City of Frederick before starting any project.