Rockville, MD Accessory Structures: ADU Rules (2026)

The Rockville Mayor and Council approved zoning text amendment TXT2023-00263 on October 9, 2023, permitting attached accessory dwelling units as a conditional use in all residential zones. The law took effect April 9, 2024. Attached ADUs may be constructed within or as an addition to an existing single-unit detached home. Key requirements include owner occupancy of either the main dwelling or the ADU for at least six months of the year, a separate entrance for the ADU, and external modifications compatible with the existing dwelling and any neighborhood design guidelines. The gross floor area of the ADU must be equal to or less than 50 percent of the total floor area of the primary dwelling, unless the ADU is in the basement or cellar. Detached ADUs in accessory buildings are under consideration by the Mayor and Council and would be limited to 50 percent of the main home floor area or 750 square feet, whichever is less. Conditional use approval is required before construction. Contact the Community Planning and Development Services Department at 240-314-8211 or zoning@rockvillemd.gov for application requirements. Maryland also passed the Accessory Dwelling Units Act of 2025, further expanding ADU rights statewide.