Building an accessory dwelling (ADU) in Arlington County

Where these rules apply

Arlington is "the geographically smallest self-governing county in the U.S." After a 1922 Virginia Supreme Court of Appeals decision, "there are no incorporated towns or cities within Arlington's boundaries." So the county's zoning ordinance covers every address in Arlington.

The rules are in section 12.9.2 of the Arlington County Zoning Ordinance (version effective June 13, 2026). For Virginia's statewide rules, see our Virginia page. [2][3]

What you can build

An accessory dwelling is "a complete independent dwelling unit, with kitchen and bath, on a lot that has a main dwelling." It must have the same owner as the main house. It can be:

• within a detached accessory building, such as a detached garage;
• within or attached to the main house, such as a basement apartment or an addition.

Is your lot eligible? The county's eligibility rules are:

• the lot is zoned R-20, R-10, R-8, R-6, R-5, R-10T, R-15-30T or R-2-7;
• it has, or will have, a one-family detached house;
• it doesn't already have an AD or a family/caregiver suite; and
• the applicant owns the property.

An AD may be created in a nonconforming house or accessory building, as long as any required alterations follow the zoning ordinance.

The ordinance text (§12.9.2) also allows ADs within or attached to semidetached or townhouse dwellings built under the county's expanded housing option rules (§10.4). The county's permit page lists only one-family detached houses, so if your home is one of those, confirm eligibility with the Zoning Division.

Use the county's Real Estate Assessments database to check your zoning district, or ask the Zoning Division. [1][2]

Size, height and setbacks

Size. An AD wholly within a basement has no set size limit beyond the basement's walls. In all other cases:

• if the main house is at least 1,000 sq ft, the AD can't exceed 750 sq ft or 35% of the combined floor area of the house and the AD;
• if the main house is under 1,000 sq ft, the AD can't exceed 500 sq ft or 45% of the combined floor area.

Floor area generally counts every floor, including attic and basement space.

New detached buildings. A detached accessory building approved after May 18, 2019 that contains an AD must meet these limits:

• height: the lesser of 1.5 stories or 25 ft;
• footprint: 560 sq ft in the R-5 and R-6 districts, 650 sq ft in other districts;
• interior lots: the nearest wall at least 5 ft from the side and rear lot lines;
• corner lots: the nearest wall at least 5 ft from any side lot line, and the eave at least 10 ft from the rear lot line;
• at least 25 ft from any street, and at least 8 ft from any wall of the main house;
• no exterior stairs to an upper-floor entrance on the side of the lot facing a street.

Older detached buildings. A detached building that existed before May 18, 2019 can be converted to an AD with no specific height, footprint or setback limits, but alterations must be interior only.

Stairs. The street-side stair rule also applies to an AD inside the main house: if its entrance is above the first floor, the exterior stairs can't be on the side of the lot facing a street. [1][2]

Parking

Parking rules for ADs are in section 14.3 of the zoning ordinance:

• if the lot has one off-street space, you must keep it;
• if it has two or more, you must keep at least two;
• if it has none, you must create one, unless a parking survey by the Department of Environmental Services finds the block is less than 65% parked.

For how long a parking survey takes and its fees, the county says to contact the Zoning Division at 703-228-3883. [1][2]

Fees and timeline

Under the county's Planning and Zoning fee schedule effective July 1, 2026, an Accessory Dwelling Permit is $582, plus a $387 Department of Environmental Services parking survey fee if a survey is required. A zoning certificate of occupancy for an accessory dwelling unit is $520. A 10% automation enhancement fee is added to the total. Building, trade and other permits have separate fee schedules, and adding plumbing fixtures may bring an impact fee from the Department of Environmental Services. See the county's fee schedules.

The county says to allow about 30 days to process an AD permit after the Zoning Division accepts the application as complete. It recommends applying for the AD permit at least two weeks before you apply for the building permit. The building permit can't be issued until the AD permit is issued and you have recorded the Declaration of Covenants. [1][4][5]

Building code issues

The county strongly recommends hiring an architect or an experienced contractor familiar with the building code. Turning part of a house into a second dwelling unit often means:

• fire-rated walls and floors (at least one hour) between the units, which may require major work or sprinklers;
• separate mechanical, electrical and plumbing systems;
• a code-compliant way out of the unit, and emergency egress windows in every bedroom;
• ceilings at least 7 ft high in habitable rooms and basements.

A new detached AD must meet all the requirements for a new house. Ask the Inspection Services Division whether the AD needs its own address; getting one can take up to three weeks. In a local historic district, any exterior work needs a Certificate of Appropriateness before you apply for other permits. [5]

Living there and renting it out

The owner must live in either the main house or the AD as a primary residence. If not, the entire property may be occupied by no more than one family. No more than three people may live in the AD.

You must file an affidavit of compliance before the certificate of occupancy, and file it again after structural changes to the AD or when the main house changes owners. The owner must allow annual inspections by the Zoning Administrator and tell tenants about them. Breaking the rules can lead to revocation of the AD permit.

Short-term rentals. Arlington allows "accessory homestay," renting all or part of your home to overnight lodgers, in a home with an AD. The resident must live there as a primary residence, at least 185 days a year. The resident may rent the main house, the AD or both to lodgers, with no more than three lodgers in the AD. You need an accessory homestay permit from the Zoning Administrator ($113, valid one year). [1][2][4]

Does Virginia's 2027 ADU law change this?

Virginia's ADU law, Va. Code 15.2-2292.4, takes effect July 1, 2027, and caps the ADU permit fee at $500 in the localities it covers. But it says "Nothing in this section shall apply to a locality that adopted an ADU ordinance prior to January 1, 2026." Arlington's zoning ordinance regulated accessory dwellings before 2026; its detached-building rules refer to approvals after May 18, 2019. Confirm with the Zoning Division how the state law applies to your project. [2][6]

Permit steps in Arlington County

1. Check eligibility and book a pre-submission meeting

   Confirm your zoning district and house type, then set up a pre-submission meeting with the Zoning Division at 703-228-3883 or zoningadmin@arlingtonva.us. [1]

2. Prepare plans and forms

   You need floor plans of the main house and the AD, a scaled site plan, a certified plat of existing improvements, the Acknowledgement and Agreement to Comply, and the Declaration of Covenants. [1]

3. Apply for the AD permit

   In Permit Arlington, click Create and select Zoning Application, then pay the filing fee. The Zoning Administrator signs and issues the AD permit if there are no issues. [1]

4. Record the covenants

   After approval, record the original Declaration of Covenants, signed by the Zoning Administrator, with the Land Records Division of the Circuit Court at 1425 N. Courthouse Rd., Suite 6200, and send the receipt to the Zoning Administrator. [1]

5. Get the building permit

   Apply for a Residential Building Permit and trade permits with the Inspection Services Division. It can't be issued until the AD permit is issued and the covenants are recorded. [1]

6. Build, file the affidavit and get a certificate of occupancy

   Schedule inspections as you build. File the Affidavit of Compliance with the Zoning Administrator, then apply for a Certificate of Occupancy; the AD is ready once it is issued. [1]

Who to call

• Arlington County Zoning Division

  AD eligibility, pre-submission meetings, AD permits and parking surveys (email zoningadmin@arlingtonva.us)

  703-228-3883

  [1][7]

• Permit Arlington Center (building permit process)

  Residential building permits, permit requirements and permit history

  703-228-3800

  [7]

• Arlington County Department of Environmental Services

  Right-of-way, driveway, and new water and sewer permits

  703-228-3629

  [7]

Questions people ask