Accessory Dwelling Unit (ADU) Rules for Gaithersburg, MD

ADU State Law

What can you build in Maryland?

• –Local-law mandate: By Oct 1, 2026, each legislative body must adopt a local law authorizing ADUs under this section.
• –Local zoning mostly remains: The subtitle generally does not alter local zoning power except as provided, but locals must establish policies that further the subtitle's intent.
• –Definition-based size cap: An ADU must be ≤ 75% of the size of the primary SF detached dwelling and subordinate in use; ADUs may be detached or attached.
• –Density/growth limits: ADUs must be excluded from density calculations and from measures limiting residential growth that pertain to the lot/parcel/tract.
• –Setbacks: Local law cannot set side/rear setbacks that exceed existing accessory-structure setbacks.
• –Parking: If a jurisdiction adds off-street parking requirements, it must consider specified factors and provide a waiver process, and must complete a parking study before adopting such requirements.
• –Alley access option: Local law may prohibit converting an accessory structure to an ADU if only vehicular access is from an alley.
• –Codes/adequate facilities: Local law must provide for ADU construction meeting public health/safety/welfare standards, including building codes and adequate public facilities provisions.