Washington DC allows accessory apartments (the District's term for ADUs) by-right in most residential zones (R-1 through R-5) under DC Zoning Regulations Subtitle U § 253. Applicants file a building permit with the Department of Buildings (DOB, formerly DCRA's permitting division). Most R-1 lots can add an internal or detached accessory apartment without zoning relief, though external accessory apartments in R-1 require special exception review by the Board of Zoning Adjustment (BZA).
DC adopted modern accessory-apartment zoning in 2016 as part of the Zoning Regulations of 2016. Under Subtitle U § 253, an accessory apartment is permitted as a matter of right in R-1-A, R-1-B, R-2, R-3, R-4, R-5, R-6, RA, and RF zones for an existing one-family dwelling, subject to standards in Subtitle U § 253.2: only one accessory apartment per lot; the principal dwelling must remain a one-family detached or semi-detached use; the accessory apartment may be internal (within the principal dwelling) or external (in an existing or new accessory building) — though external accessory apartments in R-1 zones require BZA special exception under Subtitle X. Floor area is capped at the lesser of 35 percent of the gross floor area of the principal dwelling or 900 square feet. The accessory apartment must share utilities with the principal dwelling unless separately metered. The permitting path is: (1) zoning review confirming as-of-right eligibility; (2) building permit through DOB; (3) Certificate of Occupancy. Historic districts (Georgetown, Capitol Hill, Logan Circle, etc.) require Historic Preservation Review Board (HPRB) approval for any exterior alterations.
Building an accessory apartment without a building permit: stop-work order, daily fines under DC Construction Codes, possible required removal. Use of an unpermitted accessory apartment as a rental: housing violation and tax exposure.
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See how Washington's adu permits rules stack up against other locations.
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