Local Permitting Guide
Building an Accessory Dwelling in Arlington County
⚠ 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: Arlington County Government — Accessory Dwelling Permit
Arlington County refers to ADUs as "Accessory Dwellings" (ADs), and permits them under a fairly detailed set of rules aimed at preserving neighborhood character while adding housing diversity. Here's a plain-language summary of the county's actual requirements — for project-specific eligibility, always confirm directly with Arlington's Zoning Division.
Does This Guide Apply to You?
Unlike Fairfax County, Arlington has no incorporated towns — the entire county is governed as a single jurisdiction, including:
The one exception to check is whether your specific zoning district (R-20, R-10, R-8, R-6, R-5, R-10T, R-15-30T, or R-2-7) is eligible for an AD at all — not every residential zone in the county is. See the full jurisdiction directory →
Eligibility Basics
- The lot must be zoned R-20, R-10, R-8, R-6, R-5, R-10T, R-15-30T, or R-2-7
- The lot must have (or will have) a one-family detached dwelling
- There cannot already be an AD or a family/caregiver suite on the lot
- The applicant must be the property owner
Owner-Occupancy Requirement
The property owner must use either the main dwelling or the AD as their primary residence. If neither is owner-occupied, the entire property cannot be occupied by more than one family.
Size Limits
- Basement ADs: no specific size limit — only the perimeter walls of the basement restrict size
- Above-basement, main dwelling ≥1,000 sq ft: AD cannot exceed 35% of the combined floor area of both dwellings, up to a maximum of 750 sq ft
- Above-basement, main dwelling <1,000 sq ft: AD cannot exceed 45% of combined floor area, up to a maximum of 500 sq ft
Design & Setback Requirements (Detached ADs Built After May 18, 2019)
- No exterior stairs to an entrance above the first floor on the street-facing side
- At least 25 ft from a street right-of-way line
- At least 8 ft from any wall of the main dwelling
- Height limited to the lesser of 1½ stories or 25 ft
- Footprint capped at 560 sq ft (R-5, R-6 districts) or 650 sq ft (R-20, R-10, R-8, R-10T, R-15-30T, R-2-7 districts)
- Interior lots: minimum 5 ft rear and side yard setbacks; corner lots: 10 ft rear, 5 ft side
Detached accessory buildings constructed before May 18, 2019 aren't subject to these specific height, footprint, or setback restrictions — alterations to convert them to an AD must generally stay confined to the interior.
Parking
Lots with existing off-street parking must maintain their current number of spaces. Lots with no off-street parking can still qualify for an AD if one off-street space is created, or if a county parking study finds the block is less than 65% parked.
The Permit Process
Applications go through Arlington's online Permit Arlington system as a Zoning Application, alongside a required Residential Building Permit. Review typically takes about 30 days once an application is accepted as complete. After AD Permit approval, a Declaration of Covenants must be recorded with the Circuit Court before a Building Permit can be issued, and an Affidavit of Compliance is required before the county will issue a Certificate of Occupancy.
Not sure what applies to your property?
Zoning district, lot size, and existing structures 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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