ADU rules in Washington, DC — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
DC allows accessory dwelling units (called 'Accessory Apartments') in most residential zones under 11 DCMR. Detached ADUs have a max footprint of 450 sq ft or 30% of rear yard. Attached ADUs are limited to 35% of the principal residence's gross floor area. Maximum 3 occupants per unit.
DC's 2016 Zoning Regulations (11 DCMR) allow Accessory Apartments in most residential zones. Attached ADUs can use up to 35% of the principal residence's gross floor area. Detached ADUs have a maximum footprint of the greater of 450 square feet or 30% of the rear yard area, with a maximum height of 20 feet or 2 stories. Occupancy is limited to 3 persons per accessory unit, and only one ADU is allowed per lot. Owner-occupancy is required in some zones (such as R-1). The unit must be accessible via an 8-foot-wide open-air path, or via alley access (24+ feet wide, or 15-24 feet wide if within 300 feet of the alley mouth). Georgetown R-19 and R-20 zones require a special exception from the Board of Zoning Adjustment. DOB building permits are required, with typical review within 21 business days. Fire sprinklers are required for new construction.
Unpermitted ADU construction faces stop-work orders, fines, and potential demolition orders. Occupancy violations carry separate penalties.
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See how Washington's adu rules rules stack up against other locations.
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