Baltimore County, MD Accessory Structures: ADU Rules (2026)
ADU rules in Baltimore County, MD, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Permit
- Use Permit required
- Interior max size
- 1/3 floor area or 2,000 sq ft
- Detached max size
- 1,200 sq ft (1+ acre)
- Occupancy
- Family members only
- Renewal
- Every two years
Summary
Baltimore County allows an accessory apartment as a temporary use in an owner-occupied single-family home or accessory building. It requires a Use Permit, must house only family members, cannot have separate meters, and must be renewed every two years.
The size of the accessory apartment may not exceed one third of the overall floor area of the dwelling or 2,000 square feet, whichever is less... 1,200 square feet if located on a lot one acre or greater; 800 square feet if located on a lot less than one acre.
Full Breakdown
Under BCZR Section 400.4, an accessory apartment inside the principal dwelling may not exceed one-third of the dwelling's floor area or 2,000 square feet, whichever is less. If placed in a detached accessory building, it may not exceed 1,200 square feet on a lot of one acre or greater, or 800 square feet on a smaller lot, and requires a Special Hearing before the Office of Administrative Hearings. Occupants of the apartment and the main dwelling must be family related by blood, marriage, or adoption, and the unit may not have separate utility meters. A recorded Declaration of Understanding is required.
Violations & Fines
Use Permit terminates if the apartment is no longer occupied by named family members or the property is sold; unpermitted second units are zoning violations subject to enforcement by PAI.
Frequently Asked Questions
Can I rent my accessory apartment to a tenant?
Does a detached in-law apartment need a hearing?
Sources & Official References
Other rules in Baltimore County
How Baltimore County compares: Easiest Cities to Build an ADU·Compare Baltimore County to another location·View the Maryland accessory structures overview
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