ADU rules in Arlington County, VA
Yes. An accessory dwelling is a dwelling unit and needs a building permit.
Arlington allows one accessory dwelling per lot, inside the house, attached, or in a backyard building, with a zoning administrator permit.
A detached unit needs 5 ft from the side and rear lines and can be up to 25 ft and 1 1/2 stories.
Rules last checked by a person on October 20, 2026. Guidance only; confirm with Arlington County before you build.
Limits
| Units per lot | 1 accessory dwelling (not with a family/caregiver suite) |
|---|---|
| Size | 750 sq ft or 35% of the combined floor area, whichever is less (500 sq ft / 45% if the house is under 1,000 sq ft); the whole basement if it's a basement unit |
| Detached setbacks | 5 ft side and rear (corner lots: 5 ft side, 10 ft rear to the eave); 25 ft from any street |
| Detached height | 25 ft and 1 1/2 stories |
| Detached footprint | 560 sq ft in R-5 and R-6; 650 sq ft elsewhere |
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…
- Arlington County Zoning Ordinance § 12.9.2, accessory dwellings. Checked 2026-10-20.
Accessory dwellings are allowed in R districts, subject to issuance of a permit by the zoning administrator... Not more than one accessory dwelling shall be permitted on a lot... On interior lots, the nearest wall of the accessory building shall not be loca…
- 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...