Local Permitting Guide
Building an Accessory Dwelling Unit in Alexandria
⚠ Important Notice
This page summarizes publicly available government information for general educational purposes only. HomeSprout LLC did not create this information, does not guarantee its accuracy, completeness, or currency, and is not responsible for decisions made based on it. Rules change and vary by property — always verify current requirements directly with the official source below before proceeding with a project.
Official source: City of Alexandria — Accessory Dwelling Units in Alexandria (see also Alexandria Zoning Ordinance Section 7-203)
Alexandria has had a dedicated Accessory Dwelling Unit (ADU) ordinance since City Council approved it on January 23, 2021 — codified in Zoning Ordinance Section 7-203. Here's a plain-language summary of the city's rules — for project-specific eligibility, always confirm directly with Alexandria's Department of Planning & Zoning.
Does This Guide Apply to You?
This guide applies to properties within the independent City of Alexandria:
It does not apply if your address says "Alexandria" but you're actually in unincorporated Fairfax County — commonly called "South Alexandria" (Belle Haven, Hollin Hills, Mount Vernon, Fort Hunt, Huntington, Hybla Valley, Groveton, Kingstowne, Franconia). These share an Alexandria ZIP code but are governed by Fairfax County, not the city. If that's you, see our Fairfax County guide instead.
What Qualifies
ADUs can take the form of basement apartments, converted garages, or new detached structures. Only one ADU is permitted per lot developed with a single, two-family, or townhouse dwelling.
- The ADU and the main house must remain under common ownership
- The property owner must reside in either the main house or the ADU
- No more than three persons may occupy the ADU
- The ADU's kitchen must include a sink, cooking appliance, food preparation counter, storage cabinets, and a refrigerator
Size & Setbacks for Detached ADUs
Per the Alexandria Zoning Ordinance, the maximum first-floor area of a detached accessory building is the greater of:
- 350 sq ft, for lots 2,500 sq ft or smaller
- 500 sq ft, for lots larger than 2,500 sq ft
Setbacks are notably tight compared to many jurisdictions: detached ADUs generally need only 1 ft from side and rear lot lines, increasing to 3 ft if the ADU has windows facing the nearest lot line.
Parking
Alexandria does not require additional off-street parking for an ADU — but existing required parking spaces cannot be removed to accommodate ADU construction.
Historic Districts: An Extra Step
If your property is in Old Town, Parker-Gray, or another locally designated historic district, an ADU project will also need a Certificate of Appropriateness from Alexandria's Board of Architectural Review before a building permit can be issued — in addition to the standard zoning and building permit process.
Short-Term Rentals
Short-term rental of an ADU is permitted, but the main house and the ADU cannot both be short-term rented at the same time.
Not sure what applies to your property?
Lot size, zoning, and historic district status all affect what's actually buildable. We handle the zoning determination and permitting process as part of our design-build service.
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