Building an ADU in Washington, DC

What DC's zoning rules let you build

DC isn't a state, so there is no state ADU statute. The rules are in the District's Zoning Regulations of 2016 (Title 11 of the DC Municipal Regulations). They define an accessory apartment as a unit "secondary to the principal single household dwelling unit" in floor area, intensity of use and physical character, with its own kitchen and bath and possibly a separate entrance.

In all R zones, "one (1) principal dwelling unit and one (1) accessory apartment shall be permitted per lot of record." Under 11-U DCMR 253, an accessory apartment is allowed "in a principal dwelling or an accessory building as a matter of right in the R zones, except the R-1B/GT or R 3/GT zone." In those two Georgetown zones you need a special exception from the Board of Zoning Adjustment (BZA). Section 253.4 allows it there in either the house or an accessory building, but section 253.9 says it "shall only be permitted on the second story of a detached accessory building," so confirm with DOB's zoning staff.

DOB suggests checking your zone and any overlays on the DC Office of Zoning website before you apply. [1][2][3]

Rules for every accessory apartment

• Owner occupancy: "Either the principal dwelling or accessory apartment unit shall be owner-occupied for the duration of the accessory apartment use." The BZA can't waive this in any R zone.
• Occupants: no more than three people may live in the accessory apartment. In the Georgetown zones, the house and apartment together are capped at six people.
• Modifications: the BZA may modify or waive up to two of the section's other requirements. Asking to change more than two is treated as a variance request.

[1]

An apartment inside your house

An accessory apartment in the main house must meet these conditions:

• The house must have at least 2,000 square feet of gross floor area in R-1 zones or 1,200 square feet in R-2 zones, not counting garage space.
• The apartment may not take up more than 35% of the house's gross floor area.
• A new entrance can't be on a wall facing a street. In R-3 zones it may face the street if it is below the main level of the house and, in a historic district, is found compatible with the district.

[1]

An apartment in a backyard or alley building

An apartment in an accessory building is a matter of right (outside the Georgetown zones) only if it has permanent access, by one of these:

• An open-air passage at least 8 feet wide from the building to a public street, through a side setback or a recorded shared easement
• An improved public alley at least 24 feet wide that connects to a street
• Being within 300 feet of a public street reached by an improved public alley at least 15 feet wide

The building can't have a roof deck, and it can't be used at the same time for anything other than a private garage, an artist studio or storage for a home on the lot. If you can't meet these conditions, you can apply to the BZA for a special exception. The BZA must find the building isn't likely to become objectionable to neighbors and that utilities are adequate.

Building size and placement. Accessory buildings in R zones may be up to two stories and 22 feet tall. Since July 10, 2026, the maximum footprint is the greater of 30% of the required rear yard or 650 square feet in R-1 and R-2 zones, or 550 square feet in R-3 zones. An accessory building other than a shed must be set back 7.5 feet from the centerline of any alley and 3 feet from a rear lot line, unless that line abuts an alley or street. In R-1 and R-2 zones it also needs a 3-foot side setback unless the side abuts an alley or street. All accessory buildings together can't cover more than 30% of the required rear yard. [1][2][5]

What Zoning Commission Order 25-12 changed

Z.C. Order No. 25-12, an omnibus text amendment, became "final and effective upon publication in the District of Columbia Register, that is on July 10, 2026." For ADUs, it:

• Raised the maximum accessory building footprint in R zones from the greater of 30% of the required rear yard or 450 square feet, to 650 square feet in R-1 and R-2 and 550 square feet in R-3 (and 550 square feet in RF zones)
• Added a 3-foot rear setback for accessory buildings in R zones and a 3-foot side setback in R-1 and R-2, except along an alley or street
• Reworded the existing rule that accessory apartments aren't permitted in RF zones, and added the same rule for RA and MU zones, where "principal dwelling units are permitted" instead
• Changed the rules for a principal dwelling unit in an accessory building in RF zones

The order didn't change the text of 11-U DCMR 253, and the Commission declined to lift the owner-occupancy requirement. As of October 10, 2026, the codified section on the DC Regulations site still shows its August 25, 2023 version. [1][2][5]

Getting permits from DOB

DOB handles building permits. Its overview of the permitting process lists these stages:

• Before you apply: check the zoning rules and any historic district or other overlays. A building plat certified by the DC Surveyor is required for all exterior work on one- and two-family homes. Ask for a new address if you need one.
• Apply: submit through DOB's Citizens Access Portal, then upload plans to ProjectDox using the residential checklist.
• Plan review: plans typically go through zoning, mechanical/plumbing, electrical, fire, structural, green and energy review, plus historic preservation and other agencies when they apply.
• Permit issuance: pay the remaining fees and give your contractor's information, or attest that you, as owner, are the contractor.
• Inspections: schedule building inspections as work proceeds.

DOB's permitting FAQs say a homeowner of a single or two-family home can be listed as the contractor. The fee is based on the whole project's construction cost, and the filing fee is 50% of the total permit fee. Call DOB at (202) 671-3500 with questions. [3][6][7]

Special exceptions from the BZA

You need a BZA special exception for an accessory apartment in the Georgetown zones, for one in an accessory building without the required access, or to modify up to two of the section's requirements. The BZA filing fee for an accessory apartment special exception is $325, according to the Office of Zoning's October 2025 compilation of the regulations. [1][2]

Renting your accessory apartment

The zoning rules say that before renting an accessory apartment, the owner "shall obtain a Residential Rental Business License" and have the property inspected for housing code compliance. The rule names the former Department of Consumer and Regulatory Affairs; DC's Department of Licensing and Consumer Protection now issues housing business licenses.

DLCP's "two-family rental" license covers renting "an English basement apartment, converted basement apartment, or carriage house in a single-family home where the main residence is occupied by the property owner or another tenant." It costs $219 for 2 years or $438 for 4 years. DLCP says a Certificate of Occupancy is required for two-family rentals, and you must register with the Department of Housing and Community Development after the license is issued. [1][4]

District of Columbia laws to know

• 11-U DCMR 253, Accessory Apartment (R)

  DC zoning regulation that allows one accessory apartment per lot in R zones and sets the owner-occupancy, occupancy, size and access rules. [1]

• Z.C. Order No. 25-12 (2026)

  Zoning Commission text amendments, effective July 10, 2026, that enlarged the allowed accessory building footprint, added side and rear setbacks, reworded the existing bar on accessory apartments in RF zones, and added the same bar for RA and MU zones. [5]

Questions people ask