Alexandria allows ADUs in residential zones with moderate regulations. The city's historic character and DC proximity create a strong housing market, though design guidelines add complexity.
Zoning & Size Requirements [1]
| Allowed Zones | Single-family residential (non-historic) |
| Max Size (Detached) | 900 sq ft |
| Max Size (Attached) | 750 sq ft |
| Max Size (JADU) | Not allowed |
| Max Height | 20 ft (or height of main house, whichever is less) |
| Max Units | 1 ADU per lot |
Setback Requirements [1]
| Rear Setback | 1 ft minimum; 3 ft if windows face property line |
| Side Setback | 1 ft minimum; 3 ft if windows face property line |
| Front Setback | 20 feet |
| Parking Required | 1 space per unit |
| Owner Occupancy | Not required |
| Min Lot Size | 4,500 sq ft |
Permit Process & Fees
| Approval Process | Building permit + design review |
| Review Timeline | 70-100 days |
| Permit Fees | $3,200-$5,000 |
| Impact Fees | $1,200-$2,000 |
| Plan Check | 3-4 weeks |
| Pre-Approved Plans | Limited availability |
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Construction Costs [2][3]
| Average Build Cost | $160,000-$320,000 |
| Cost per Sq Ft | $180-$360 |
| Garage Conversion | $85,000-$190,000 |
| Prefab ADU (Installed) | $125,000-$280,000 |
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Rental Income Potential [4][5]
| Avg Rent (1 Bedroom) | $1,650-$2,150/mo |
| Avg Rent (2 Bedroom) | $2,050-$2,900/mo |
| Short-Term Rental | Not permitted |
| Est. Annual ROI | 5-7% annual return |
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Recent Law Changes
What's Changed Recently
- Arlington ADU ordinance update (2026): Increased max height to 25 ft for detached ADUs
- Alexandria expanded ADU program with pre-approved plan sets (2026)
- Virginia state legislature reviewing ADU enabling legislation for 2026
- Northern Virginia regional ADU working group established for cross-jurisdiction standards
Tips for Building an ADU in Alexandria
- Historic preservation is important consideration; verify zone compatibility
- Design review adds 70+ day timeline; plan accordingly
- Premium DC market supports high rents despite moderate ROI
- Walkable waterfront location attracts quality tenants
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- Accessory Dwelling Units in Alexandria — City of Alexandria Planning Department — Accessed 2026-02-25
- HomeAdvisor — ADU Construction Cost Data Market Data — Accessed 2026-02-24
- Angi — Local ADU Contractor Costs Market Data — Accessed 2026-02-24
- Zillow Rental Manager — Market Rent Data Market Data — Accessed 2026-02-24
- HUD Fair Market Rents Government Data — Accessed 2026-02-24
Frequently Asked Questions
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