ADU rules in Alexandria, VA
Yes. An accessory dwelling is a dwelling unit and needs a building permit.
One accessory dwelling per lot, inside the house or in a backyard building, with no extra parking required.
A backyard unit can be 1 ft from the side and rear lines (3 ft if windows face the line).
Rules last checked by a person on October 20, 2026. Guidance only; confirm with Alexandria before you build.
Limits
| Units per lot | 1 accessory dwelling, with a single-unit, two-unit or townhouse dwelling |
|---|---|
| Detached size | First floor up to 1/3 of the house's first floor or 500 sq ft, whichever is greater (350 sq ft on lots of 2,500 sq ft or less) |
| Inside the house | Up to 1/3 of the house's gross floor area |
| Detached setbacks | 1 ft side and rear; 3 ft where windows or doors face the line; more for parts over 13.5 ft |
| Detached height | 20 ft or the house's height, whichever is less |
| Parking | None required |
Good to know
- From July 1, 2027, Virginia localities must allow ADUs by right in single-family districts, with a $500 permit-fee cap and no setbacks stricter than for other accessory structures (SB 531).
- Call 811 at least a few days before you dig footings or post holes. Utility locating is free.
- HOA covenants and deed restrictions can be stricter than city rules. Check yours before you build.
Check your lot
Where to apply
Sources
- Virginia USBC, 13VAC5-63-80 Section 108.2, Exemptions from application for permit. Checked 2026-10-20.
2. One story detached structures used as tool and storage sheds, playhouses, or similar uses, provided the building area does not exceed 256 square feet... 5. Fences of any height unless required for pedestrian safety as provided for by Section 3306 or used…
- City of Alexandria Zoning Ordinance § 7-203, accessory dwellings (Municode, Supp. 103). Checked 2026-10-20.
Only one accessory dwelling shall be permitted on any recorded lot... The gross floor area of an accessory dwelling within a principal dwelling shall not exceed one-third of the principal dwelling's gross floor area... The maximum floor area of the accessor…
- 44 CFR 59.1, definition of development (NFIP). Checked 2026-10-19.
Development means any man-made change to improved or unimproved real estate, including but not limited to buildings or other structures...
- 44 CFR 60.3, floodplain management criteria. Checked 2026-10-19.
Require permits for all proposed construction or other development in the community...