Washington, DC Accessory Structures: ADU Rules (2026)
ADU rules in Washington, DC, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Apartments allowed per lot
- 1, matter of right in most R zones
- Occupancy cap
- 3 people (6 combined in R-1B/GT, R-3/GT)
- Floor-area cap
- 35% of house's gross floor area
- Min. house size, in-house unit
- 2,000 sq ft (R-1), 1,200 sq ft (R-2)
- Detached-building units
- Need permanent code-specific access, no roof deck
Summary
The District allows one accessory apartment per lot in residential zones under 11 DCMR-U § 253, capped at 35% of the house's gross floor area and three occupants (six if it's in the R-1B/GT or R-3/GT zone), with size and access conditions that differ for units inside the main house versus a separate accessory building.
One (1) accessory apartment may be established in an R zone, subject to the provisions of this section... The total number of persons that may occupy the accessory apartment shall not exceed three (3), except in the R-1B/GT or R-3/GT zone where the aggregate number of persons that may occupy the house, including the principal dwelling and the accessory apartment combined, shall not exceed six (6)... The accessory apartment unit may not occupy more than thirty-five percent (35%) of the gross floor area of the house;
Full Breakdown
4 extends that matter-of-right status to apartments placed either in the principal dwelling or in an accessory building, except in the R-1B/GT and R-3/GT zones, where an accessory apartment instead needs Board of Zoning Adjustment approval as a special exception. 6 caps occupancy at three people in the accessory apartment itself, except in the R-1B/GT or R-3/GT zone, where the combined household in the principal dwelling and accessory apartment together cannot exceed six people. 7 sets a minimum house size of 2,000 square feet of gross floor area in the R-1 zone and 1,200 square feet in the R-2 zone, and limits the accessory unit itself to no more than 35% of the house's gross floor area; any new entrance generally cannot face the street, though R-3 zones allow a below-grade street-facing entrance if a historic-district review clears it.
8 instead requires permanent, code-specific access (an 8-foot open passage, a 24-foot public alley, or proximity to a 15-foot alley within 300 feet), bars a roof deck on the building, and limits any other use of that building to a garage, artist studio, or storage.
Violations & Fines
Building or renting an accessory apartment that exceeds the 35% floor-area cap, the three or six-person occupancy limit, or the access standards of § 253.8 without an approved special exception is a zoning violation. Under 11 DCMR § 305.1, the owner faces a fine of up to $100 per day the violation continues, and § 305.2 lets the Attorney General or a specially harmed neighbor seek an injunction against the unlawful use.
Frequently Asked Questions
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Sources & Official References
Other rules in Washington
How Washington compares: Easiest Cities to Build an ADU·Compare Washington to another location·View the District of Columbia accessory structures overview
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