ADU Rules in Alexandria, Virginia

Alexandria is an independent city in Northern Virginia with approximately 160,000 residents. This is a critical distinction: Alexandria is NOT part of Fairfax County. Despite being physically surrounded by Fairfax County and Arlington County, Alexandria operates as its own fully independent jurisdiction with its own mayor, city council, city manager, planning department, and zoning code. Properties in Alexandria are governed entirely by City of Alexandria regulations — not Fairfax County or Arlington County rules.

Alexandria sits on the Potomac River directly across from Washington, D.C., and is served by the King Street Metro (Blue/Yellow lines) and other Metro stations. Its position in the DC metro area, walkable historic streets, and transit access make it one of Virginia's most expensive housing markets. ADUs are highly valuable here for both rental income and additional housing, but the city's robust historic preservation framework adds complexity for properties in protected districts.

Virginia statewide ADU law status

Virginia has no enacted statewide ADU preemption. SB 304 of 2024 would have required ADUs by-right but was deferred to the Virginia Housing Commission. Va. Code § 15.2-2292.1 governs only temporary family health-care structures, not general ADUs. ADU rules are set by local zoning ordinance — contact the local planning department.

Alexandria Local Zoning for ADUs

Alexandria's zoning ordinance (the Zoning Ordinance of the City of Alexandria) was comprehensively updated in recent years. Residential zones include R-2-5, R-5, R-8, and others. ADU standards in single-family zones generally include:

• Maximum size: ADUs are typically limited to 1,200 square feet or a percentage of the primary dwelling's floor area
• Unit count: One ADU per single-family lot
• Types: Detached ADU (new structure in rear yard), attached ADU (addition), internal ADU (basement or above-garage conversion), and junior ADU (within existing single-family home)
• Setbacks: Detached ADUs must meet rear and side setbacks; Alexandria's older lots can be quite small, so setback compliance requires careful measurement
• Height: Detached ADUs are typically limited in height to protect neighborhood character
• Lot coverage: Must not exceed district maximums, which can be tight on smaller urban lots
• Parking: State law limits parking requirements for ADUs near transit; Alexandria's Metro access may qualify many properties

Contact the Alexandria Planning and Zoning Department at (703) 746-4200 or visit alexandriava.gov/planning for current ADU ordinance provisions.

Historic Districts — A Major Consideration

Alexandria's historic preservation rules are among the most rigorous in Virginia. Key designations include:

• Old Town Alexandria: A National Historic Landmark District with extensive local protections. The Board of Architectural Review (BAR) — Old Town reviews all exterior changes to structures in this district for design compatibility. Adding a visible detached ADU in a rear yard, or any exterior alteration that changes the historic character of the primary structure, requires BAR approval.
• Parker-Gray Historic District: Locally designated district in the Del Ray/Parker-Gray area; also subject to BAR review.
• Other locally designated districts: Check with Planning for current district boundaries.

Practical implications for ADUs:

• Interior ADUs (basement apartments, above-garage conversions with no exterior changes) typically do not require BAR review and are much easier to permit in historic areas
• Detached ADUs in rear yards require BAR approval in designated historic districts; the BAR evaluates massing, materials, architectural character, and visibility from public rights-of-way
• BAR review adds time (typically 30-60 days for a hearing slot) and requires additional design documentation
• The city has staff who can provide pre-application guidance on what BAR expects

Potomac River and Flood Zones

Alexandria's waterfront along the Potomac River includes areas in FEMA Special Flood Hazard Areas, particularly near the Old Town waterfront and low-lying areas. The Potomac can experience significant flooding during storm surge and heavy rain events. Properties in flood zones must meet Base Flood Elevation requirements for new construction, including ADUs. Check your flood zone designation at msc.fema.gov.

Alexandria also has areas with stormwater management requirements; new impervious surface from a detached ADU may trigger stormwater management plan review.

Permitting Process

1. Confirm jurisdiction — Verify your address is in the City of Alexandria (not Fairfax County or Arlington County)
2. Check historic district status — Determine if your property is in a BAR-regulated historic district
3. Flood zone check — Verify FEMA flood zone at msc.fema.gov
4. Pre-application consultation — Alexandria Planning and Zoning, (703) 746-4200
5. BAR pre-application (if in historic district) — Contact the BAR coordinator early
6. Building permit application — Submit to T&ES Permits Division
7. BAR hearing (if required) — Coordinate timing with the building permit process
8. Inspections and Certificate of Occupancy — Required before occupancy

Contact Information

• Alexandria Planning and Zoning: (703) 746-4200 | alexandriava.gov/planning
• Building Permits: (703) 746-4200
• Board of Architectural Review: alexandriava.gov/BarOldTown
• Municipal Code (Zoning Ordinance): library.municode.com/va/alexandria/codes/zoning

Disclaimer: This guide provides general information only and is not legal or planning advice. Zoning regulations, historic district boundaries, and flood maps change over time. Always verify current requirements directly with the City of Alexandria Planning and Zoning Department. Do not confuse City of Alexandria regulations with Fairfax County or Arlington County regulations — they are separate jurisdictions.