Everything homeowners ask about building an ADU in Arlington — answered with 2026 data.
Yes, ADUs are allowed in R-20, R-10, R-8, R-6, R-5, R-10T, R-15-30T and R2-7 districts, on a lot with a one-family detached dwelling (§12.9.2; county AD Permit page). ADs may also be within or attached to semidetached/townhouse dwellings built under the Expanded Housing Option, §10.4. Not allowed on a lot that already has a family/caregiver suite (§12.9.2.A.1(a)). ADs are allowed by permit of the Zoning Administrator; no County Board hearing. in Arlington, VA. The maximum size for a detached ADU is Gross floor area capped at the lesser of 750 sq ft or 35% of the combined floor area of house plus AD when the house is at least 1,000 sq ft; 500 sq ft or 45% when the house is under 1,000 sq ft (§12.9.2.A.2(e)). A detached accessory building approved after May 18, 2019 may hold an AD only if its footprint is 560 sq ft or less in R-5/R-6, 650 sq ft or less in the other R districts (§12.9.2.A.2(d)). GFA counts attic and basement space (§3.1.1). Attached ADUs can be up to Same 750 sq ft/35%. Arlington has an ADU-friendliness score of 6/10. Check our full Arlington ADU rules page for complete zoning details.
ADU construction in Arlington typically costs $150,000-$350,000. The cost per square foot averages $200-$400. Garage conversions are more affordable at $80,000-$160,000, while prefab ADUs cost $150,000-$300,000. Permit fees add AD Permit $582 plus $387 if a DES parking survey is needed (FY2027 Planning and Zoning fee schedule, effective July 1, 2026). Building permit $1.70 per sq ft for new construction/additions or $0.63 per sq ft for alterations, plus a 2% state levy and a 10% automation surcharge; CO for an AD $520. to your budget. See our detailed Arlington ADU cost guide.
Detached ADUs in Arlington can be up to Gross floor area capped at the lesser of 750 sq ft or 35% of the combined floor area of house plus AD when the house is at least 1,000 sq ft; 500 sq ft or 45% when the house is under 1,000 sq ft. Attached ADUs are limited to Same 750 sq ft/35%. Junior ADUs (JADUs) have a cap of Not a category in Arlington. The separate 'family/caregiver suite' permit ($603 zoning fee, FY2027) is for relatives or caregivers only and cannot coexist with an AD on the same lot (§12.9.2.A.1(a)). Maximum height is A detached accessory building approved after May 18, 2019 that contains an AD may not exceed 25 ft or 1.5 stories, whichever is less (§12.9.2.A.2(c)). Existing pre-May 2019 accessory buildings converted with interior-only alterations carry no AD-specific height limit (§12.9.2.A.2(a)). ADs inside the house follow the main-dwelling height for the district. You are allowed up to One accessory dwelling per lot on a qualifying lot.
Rear setback: New detached AD building: 5 ft to the wall on interior lots; 10 ft to the eave on corner lots (§12.9.2.A.2(b)). The general §3.2.6 rule that no accessory building may be closer than 8 ft to any wall of the main dwelling also applies. Side setback: New detached AD building: 5 ft to the wall on interior and corner lots (§12.9.2.A.2(b)(1)-(2)). Front setback: The nearest wall of a detached building containing an AD must be at least 25 ft from any street or designated right-of-way line (§12.9.2.A.2(b)(3)) and at least 8 ft from any wall of the main dwelling (§3.2.6). No exterior stairs to an above-first-floor AD entrance on the street-facing side of the lot (§12.9.2.A.2(f)). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
No new space is required if the lot already has one or more off-street spaces - existing spaces must be kept (1 or 2 kept; at least 2 kept if more exist). A lot with no off-street parking must add one space unless a County parking survey finds the block less than 65% parked (§14.3 table; $387 DES parking-survey fee, FY2027). Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Required: the owner of the main dwelling must occupy either the main dwelling or the AD as their primary residence; otherwise the whole property may be occupied by only one family (§12.9.2.C.3). A covenant is recorded before the building permit; an affidavit of compliance is filed before the certificate of occupancy and again on any structural change or sale (§12.9.2.C.1, C.4). SB 531 (2026) does not change this: Code §15.2-2292.4(I) exempts localities whose ADU ordinance predates Jan 1, 2026. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Arlington is typically About 30 days for the AD Permit once the Zoning Division accepts the application as complete (county AD Permit page); the county recommends filing it at least two weeks before the building-permit application. No published review time for the residential building permit. Plan check: Zoning reviews the AD Permit and the building permit for §12.9.2, §3.2 and §14.3 compliance ($260 zoning review for a detached garage/accessory structure or $384 for an interior alteration to a one-family dwelling, FY2027); ISD reviews to the Virginia Uniform Statewide Building Code. Trade permits: electrical minimum $186, mechanical $149, plumbing $149. Pre-approved plans availability: Not available.
Average ADU rental income in Arlington: 1-bedroom units rent for $2,100-$3,300/month, 2-bedroom units for $2,300-$3,700/month. Short-term rentals: Allowed only as an 'accessory homestay' with a separate one-year permit ($113 zoning fee): the host must live on the property at least 185 days a year, may rent the main house, the AD or both to lodgers, and the AD is li. Expected ROI: 7-14% gross annual return.
The minimum lot size for an ADU in Arlington is No AD-specific minimum lot size. Eligibility is by zoning district (R-20 through R2-7) plus a one-family detached dwelling; the AD and any new detached building must meet the district's Article 3 and Article 5 coverage and dimensional standards (§12.9.2.A.2). A nonconforming house or accessory building may still be used, per Article 16. This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Arlington, a garage conversion typically costs $80,000-$160,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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