ADU Rules in Arlington County, Virginia

Arlington is a county — specifically Arlington County — in Northern Virginia, directly across the Potomac River from Washington, D.C. This is a critical distinction: Arlington is NOT an independent city. Unlike Virginia's 38 independent cities, Arlington County retains county status and is governed by a county board and county manager, not a mayor and city council. Arlington County has no incorporated municipalities within it — it is one of the few "urban counties" in the United States where the entire county functions as a single planning and zoning jurisdiction.

Arlington County is home to the Pentagon (the world's largest office building by floor area), Crystal City (now called National Landing), Amazon HQ2, and some of the most densely developed Metro-served urban neighborhoods in the DC area. Arlington's Rosslyn-Ballston corridor and Jefferson Davis Highway corridor are among the most transit-rich areas in the mid-Atlantic region. Housing costs in Arlington are among the highest in Virginia, making ADUs financially very attractive for homeowners.

Virginia statewide ADU law status

Virginia has no enacted statewide ADU preemption: SB 304 (2024) would have required by-right ADUs, but was deferred to the Virginia Housing Commission and not enacted. Va. Code § 15.2-2292.1 covers only temporary family health-care structures. Arlington has been proactive about housing policy and has been working to expand ADU access through its own zoning ordinance and housing-affordability goals. Administrative approval is required for conforming proposals.

Arlington County Zoning for ADUs

Arlington County's zoning ordinance (the Arlington County Zoning Ordinance, or ACZO) was comprehensively updated in recent years. Single-family residential districts in Arlington include R-5 through R-20 (based on minimum lot size) and the newer RA districts. Typical ADU standards include:

• Maximum size: Generally limited to 1,200 square feet or a percentage of the primary dwelling floor area; confirm current limits with the Planning Division
• Unit count: One ADU per single-family lot; Arlington has also been exploring allowing greater density in transit-served areas
• Types: Detached (new accessory structure), attached (addition to primary dwelling), or internal (basement, above-garage, or attic conversion)
• Setbacks: Detached ADUs must comply with the district's rear and side setbacks; Arlington's lots in single-family zones are generally moderate to small, so setback compliance is important
• Height: Typically one story or 16 feet for detached ADUs; may allow two stories if an above-garage conversion within existing structure
• Lot coverage: Must not exceed district maximums; Arlington has relatively modest lot coverage limits in its single-family zones
• Parking: Set by the county's own zoning ordinance; Arlington's Metro-rich environment may inform local parking minimums for ADUs

Contact the Arlington County Planning Division at (703) 228-3525 or visit arlingtonva.us/government/programs/planning for current provisions. Arlington's zoning has been recently updated; always use the current ordinance text.

Pentagon and Military Presence

The Pentagon is in Arlington County and is among the world's most significant military installations. However, the Pentagon does not generate AICUZ overlays applicable to residential development in surrounding neighborhoods in the same way that an airfield does — it is an office complex rather than an air operations facility. The DCA (Reagan National Airport) runway approach paths do pass over some Arlington neighborhoods, primarily in the Crystal City/National Landing area, creating aircraft noise. This is generally a quality-of-life consideration rather than a zoning prohibition on ADU construction. Verify with Arlington Planning if your property falls within any noise overlay from DCA.

Transit-Oriented Context

Arlington's Metro stations (Orange, Blue, Silver, and Yellow lines) serve the Rosslyn-Ballston corridor and the Route 1 (Jefferson Davis) corridor. Neighborhoods near Metro stations are characterized by high density and active development. Arlington's planning policies emphasize transit-oriented development; check the ACZO for any transit-proximity provisions in the current ADU standards.

Flood Zones and Stormwater

Some lower-lying areas of Arlington — particularly near Four Mile Run and other stream corridors — are in FEMA Special Flood Hazard Areas. Properties near these waterways must meet Base Flood Elevation requirements for new construction, including ADUs. Arlington has an active stormwater management program; new impervious surface from a detached ADU may trigger stormwater management review depending on the size and location. Verify your flood zone status at msc.fema.gov.

Historic Resources

Arlington has several historic overlay districts and historic resources, including portions of Clarendon, Ballston, and other neighborhoods. The county's Historic Affairs and Landmark Review Board (HALRB) reviews changes to locally designated landmarks and historic districts. Verify whether your property is in a historic overlay before finalizing ADU plans.

Permitting Process

1. Confirm it's Arlington County (not Alexandria or Fairfax County) — Verify jurisdiction
2. Check zoning district — Use the Arlington County GIS or contact Planning Division
3. Verify flood zone — Check msc.fema.gov if near Four Mile Run or other streams
4. Check historic overlay — Determine if HALRB review is required
5. Pre-application consultation — Arlington County Planning Division, (703) 228-3525
6. Building permit application — Submit to the Department of Environmental Services, Inspection Services Division
7. Inspections and Certificate of Occupancy — Required before occupancy

Contact Information

• Arlington County Planning Division: (703) 228-3525 | arlingtonva.us/government/programs/planning
• Inspection Services Division: (703) 228-3800
• Zoning Division: (703) 228-3883
• County Zoning Ordinance: arlingtonva.us/government/departments/community-planning-housing-development/zoning

Disclaimer: This guide provides general information only and is not legal or planning advice. Zoning regulations change over time. Always verify current requirements directly with Arlington County Planning and the official Arlington County Zoning Ordinance (ACZO). Note that Arlington County rules do not apply to neighboring Alexandria or Fairfax County — they are separate jurisdictions.