Arlington County

Because Arlington County contains NO incorporated towns or sub-jurisdictions, all Accessory Dwelling permitting across the entire county is handled by a single set of county offices — there is no 'unincorporated vs. incorporated' distinction as in Fairfax (where Herndon / Vienna / Clifton operate independently) or as in most other Virginia counties. Every residential parcel within the Arlington County boundary submits through the same county process. Accessory Dwelling permitting is administered primarily by the Arlington County Department of Community Planning, Housing and Development (CPHD), with the CPHD Zoning Division handling the Accessory Dwelling zoning review and the CPHD Inspection Services Division handling building permits, trade permits, and inspections. Under the post-2020 Section 12.9 framework, almost all Accessory Dwelling applications follow a single administrative by-right path: (a) applicant files an Accessory Dwelling application through the Permit Arlington online portal with site plan, floor plans, elevations (for detached ADs), parking-space demonstration or transit-proximity justification for waiver, and signed owner-occupancy affidavit; (b) the Zoning Administrator reviews for Section 12.9 compliance, typically within 30-45 days for administratively-complete applications; (c) on approval, applicant proceeds to building permit through the same Permit Arlington portal with construction documents sealed by a Virginia-licensed architect or engineer for any structural work, reviewed by the CPHD Inspection Services Division under the 2021 Virginia Uniform Statewide Building Code (adopted locally with the Virginia Uniform Statewide Building Code mandated state floor); (d) trade permits for electrical, plumbing, and mechanical work; (e) construction with inspections (footing, slab, framing, rough-in electrical / plumbing / mechanical, insulation, final); (f) Certificate of Occupancy issued by CPHD Inspection Services on final inspection pass. Parcels requiring Chesapeake Bay Preservation Act RPA review, FEMA floodplain review, or Historic District review follow parallel sub-processes that add specific procedural steps. The small fraction of Accessory Dwelling projects that cannot meet Section 12.9 standards by right (e.g., larger than 750 sqft, taller than 20 feet, non-conforming setbacks) require a variance from the Board of Zoning Appeals (BZA) via a noticed public hearing under Va. Code § 15.2-2309 — a path used rarely but available.

Process overview: Accessory Dwelling approval in Arlington County follows: (a) applicant reviews the AD standards at Section 12.9 and the CPHD AD guidance page to confirm by-right eligibility (most projects qualify under the post-2020 framework); (b) recommended pre-application consultation with the Zoning Division to confirm parcel-specific setbacks, lot coverage, height, and transit-proximity parking-waiver eligibility, particularly for detached ADs; (c) applicant submits Accessory Dwelling application through Permit Arlington with site plan showing principal dwelling and AD location (including setback measurements to all property lines), floor plans demonstrating compliance with 750 sqft / 35%-of-principal size cap or 650 sqft existing-structure-conversion cap as applicable, elevations for detached ADs with height dimension, parking-space calculation or documented transit-proximity waiver, and signed owner-occupancy affidavit; (d) CPHD Zoning Division reviews for Section 12.9 compliance, issues administrative approval typically within 30-45 days for complete applications; (e) applicant submits building permit through Permit Arlington with construction documents (sealed for structural work on detached ADs), reviewed by CPHD Inspection Services under the Virginia Uniform Statewide Building Code; (f) trade permits for electrical, plumbing, and mechanical — Arlington requires separate trade permits pulled by Virginia-licensed tradespeople; (g) construction with inspections scheduled through Permit Arlington (footing, slab, framing, rough-in electrical / plumbing / mechanical, insulation, final); (h) Certificate of Occupancy on final inspection pass with owner-occupancy covenant recorded in the Circuit Court land records. For parcels in a Chesapeake Bay Preservation Act Resource Protection Area (RPA) — mostly creek corridors along Four Mile Run, Donaldson Run, Windy Run, Lubber Run, and Pimmit Run — the CPHD Chesapeake Bay Program review adds a Water Quality Impact Assessment step. For parcels in a FEMA Special Flood Hazard Area (a small but significant subset along Four Mile Run and tidal Potomac frontage near Rosslyn, Roaches Run, and Daingerfield Island), the Floodplain Administrator review adds elevation / flood-vent / Elevation Certificate requirements. For parcels in one of Arlington's Local Historic Districts (Maywood, Ashton Heights, Lyon Village, Buckingham, Fort Myer Heights, Colonial Village, Westover), a Certificate of Appropriateness from the Historical Affairs and Landmark Review Board (HALRB) is required and adds 60-120 days.

Impact fees: Virginia counties have narrow statutory authority to charge development impact fees (Va. Code § 15.2-2317 et seq., with most fee authority limited to roads and requiring specific County Board adoption and formula-driven computation). Arlington County imposes modest site-plan and zoning application fees and building permit fees that are cost-recovery based, but does NOT charge a California-style per-square-foot impact fee schedule on Accessory Dwellings. The core costs of an Accessory Dwelling permit in Arlington County are (i) the Accessory Dwelling zoning application fee — approximately $200-$400 as of early 2026, materially lower than Fairfax's Special Permit fees because Arlington's path is administrative by-right rather than a public-hearing process; (ii) building permit fees under the adopted fee schedule, which scale with construction valuation (a typical detached Accessory Dwelling at $150,000-$250,000 valuation incurs roughly $2,000-$3,500 in building-permit fees); (iii) trade permit fees for electrical, plumbing, and mechanical work (roughly $100-$300 each, cost-recovery); (iv) Arlington County Department of Environmental Services (DES) Water / Sewer connection or availability fees — Accessory Dwelling service is typically added to the principal dwelling's existing connection without a separate new connection fee, though capacity upgrades are required for older small-diameter service lines and are billed separately; (v) Chesapeake Bay Program Water Quality Impact Assessment fees for RPA-adjacent parcels; (vi) HALRB Certificate of Appropriateness fees for parcels in a Local Historic District. School impact fees are not authorized for general locality use in Virginia; Arlington County does not impose them on Accessory Dwellings or any other residential construction. Under Section 12.9 and Permit Arlington's published fee schedule, the total out-of-pocket governmental cost for a straightforward detached Accessory Dwelling in Arlington is typically in the $3,000-$7,000 range — meaningfully lower than Fairfax Special Permit ALUs, which commonly run $7,000-$15,000+ in governmental fees due to the required Special Permit and advertising costs. (schedule)

The Arlington County Department of Real Estate Assessments (commonly referred to as the county assessor) maintains parcel-level assessment records for all real property in the county. Because Arlington contains no incorporated towns and no sub-jurisdictions, the Department of Real Estate Assessments is the sole assessing authority for every residential parcel in the county — there is no parallel municipal assessor to deal with. Virginia mandates assessment at 100% fair market value under Code of Virginia Title 58.1; unlike California's Proposition 13 acquisition-value system, Virginia localities reassess periodically using mass-appraisal methods. Arlington County reassesses real estate ANNUALLY under Va. Code § 58.1-3253 — notices are mailed in mid-JANUARY each year (earlier than Fairfax's late-February cycle) showing assessed values as of January 1 of the tax year. An Accessory Dwelling addition is captured in the following year's annual reassessment as a market-value adjustment reflecting the physical improvement and comparable-sales evidence; there is no California-style 'supplemental roll' separate from the main annual roll. Because Arlington reassesses annually, an AD completed mid-year will appear on the next January's assessment notice. Virginia has no Prop 13 cap; the statewide real-estate-tax rate Arlington sets applies to full fair market value (the calendar year 2025 tax rate was $1.033 per $100 assessed value, slightly lower than Fairfax's $1.125 base rate but applied to Arlington's higher median property values). Arlington's very high median property values (second-highest in Virginia after the City of Falls Church) mean the annual tax impact of an Accessory Dwelling is substantial in absolute dollars, though proportionally similar to other Northern Virginia jurisdictions.

Assessment policy: Virginia Code Title 58.1 requires assessment at 100% fair market value. Arlington County reassesses annually under § 58.1-3253, with January 1 as the effective date and notices mailed in MID-JANUARY — about six weeks earlier than Fairfax's late-February cycle. For Accessory Dwelling additions, the assessor incorporates the new improvement into the next annual assessment cycle — there is no separate supplemental notice as in California. Typical Arlington County AD assessed-value increments for 650-750 sqft detached units or internal conversions range from roughly $200,000 to $400,000 in the post-2024 market (reflecting Arlington's very high median property values and Northern Virginia construction costs), producing a property-tax increment of roughly $2,000 to $4,100+ per year at the $1.033 per $100 assessed-value base rate (plus small special-district adders where applicable, though Arlington has fewer and narrower special districts than Fairfax). The principal dwelling's assessed value is also revisited each year, so any market appreciation of the principal dwelling is captured alongside the AD addition. Unlike Proposition 13 jurisdictions, Virginia provides no acquisition-value cap, no 2% annual-growth cap, and no separate 'new construction supplemental' assessment with its own appeal window. Arlington publishes annual 'Notice of Assessment Change' documents and neighborhood-level sales analyses each year in conjunction with the annual reassessment, giving owners visibility into how the mass-appraisal models are tuned and allowing comparable-sales research.

Arlington County administers several county- and state-level overlay regimes that materially affect Accessory Dwelling siting: (1) the Chesapeake Bay Preservation Act (CBPA) Resource Protection Area (RPA) and Resource Management Area (RMA) buffers, mandated by Va. Code § 62.1-44.15:67 et seq. and administered locally through the Arlington County Chesapeake Bay Preservation Ordinance (Chapter 61 of the Arlington County Code) and the ACZO — RPA buffers protect all tidal shores, tidal wetlands, connected non-tidal wetlands, and perennial non-tidal streams at 100 feet, while RMA buffers extend the water-quality zone to a wider countywide footprint (and because Arlington is an 'Intensely Developed Area' under CBPA regulations, RMA effectively covers the entire county); (2) the Arlington County Floodplain Management Ordinance (Chapter 48 of the County Code, incorporated into ACZO Section 10.1) covering FEMA Special Flood Hazard Areas along the tidal Potomac River (Rosslyn waterfront, Roaches Run, Gravelly Point / Daingerfield Island area), Four Mile Run (the principal freshwater flood corridor transecting South Arlington from Bailey's Crossroads through Shirlington and Crystal City to the Potomac), Long Branch, Lubber Run, Donaldson Run, Windy Run, and Pimmit Run; (3) Local Historic Districts (LHDs) under ACZO Section 11.3 and Chapter 31.1 of the County Code — the seven designated Local Historic Districts are Maywood, Ashton Heights, Lyon Village, Buckingham, Fort Myer Heights, Colonial Village, and Westover, each with its own design guidelines and HALRB review scope; (4) the Reagan Washington National Airport (DCA) approach and departure corridors — Arlington's southern and eastern boundary is defined in part by DCA (the airport is on reclaimed land immediately across the Potomac / Boundary Channel from the Pentagon, with the 14th Street Bridge approach directly over Arlington), producing FAA Part 77 imaginary surfaces and DCA DNL noise contours that cover much of South Arlington (Aurora Highlands, Long Branch Creek, Crystal City residential pockets, Alcova Heights); (5) Joint Base Myer-Henderson Hall (Fort Myer) does have an Air Installation Compatible Use Zone component at Davison Army Airfield 14 miles south at Fort Belvoir (not Arlington), but Fort Myer itself is a garrison installation with limited aviation footprint — a small helicopter pad at Fort Myer is used for ceremonial and administrative flights to the Pentagon helipad and does not have a formal AICUZ. Coastal Commission jurisdiction does NOT apply (Virginia has no California-style Coastal Commission; CBPA is the functional analog). Very High Fire Hazard Severity Zones are NOT a Virginia regulatory category — Arlington has no WUI overlay comparable to California's CAL FIRE VHFHSZ system, and the dense urban fabric with virtually no wildland-urban interface makes fire-zone overlay moot. Seismic retrofit zones do not apply in Virginia.

• Chesapeake Bay Preservation Act Resource Protection Area (RPA) — 100-foot buffer — and Resource Management Area (RMA) — Accessory Dwelling designs that cantilever over, or place impervious surface within, the 100-foot RPA buffer require an RPA Exception. Arlington's RPA Exception process involves a Water Quality Impact Assessment (WQIA), CPHD Chesapeake Bay Program Environmental Review, and in more impactful cases a Planning Commission review. Adding 45-90 days to the overall AD timeline for an RPA Exception is typical. Parcels along Four Mile Run (much of Shirlington, Nauck, Green Valley, Aurora Highlands, Crystal City residential), Lubber Run (Lubber Run Park area, Columbia Heights / Penrose neighborhoods along the creek), Donaldson Run (Rock Spring, Yorktown, Dover Crystal neighborhoods), Windy Run (Windy Run Park area in far North Arlington), and Pimmit Run (northwestern boundary with Falls Church and McLean) should confirm RPA status via the Arlington County Map Gallery RPA viewer before design. Because Arlington is an Intensely Developed Area, RMA provisions apply to every parcel countywide — new impervious surface anywhere in the county requires stormwater best-management-practice review under Chapter 60 of the County Code (Chesapeake Bay-related stormwater regulations).
• Arlington County Floodplain Management Ordinance — FEMA NFIP participant — Accessory Dwellings in an SFHA must have lowest floor elevated to or above Base Flood Elevation plus Arlington's freeboard (the county adopted a 2-foot freeboard for residential construction in 2014, exceeding the FEMA 1-foot minimum), flood vents on any enclosed area below BFE, structural anchoring, and a post-construction Elevation Certificate. Arlington's substantial-improvement trigger uses a single-permit cycle rather than a 10-year cumulative lookback (a meaningful distinction from Fairfax's 10-year cumulative approach), so individual AD permits are evaluated for the 50% threshold in isolation. Owners along Four Mile Run (Nauck / Green Valley, Shirlington, Long Branch Creek, Crystal City residential), Long Branch, Lubber Run, Donaldson Run, Windy Run, and Pimmit Run should verify current FIRM status (2013 effective panels plus LOMRs through 2024-2025) via the county's Flooding page and the FEMA Map Service Center before AD design. Flood insurance is federally required for SFHA parcels with federally-backed mortgages.
• Airport noise and safety zones — Reagan Washington National Airport (DCA) primary; Dulles (IAD) and Joint Base Andrews secondary — Accessory Dwelling siting inside DCA's Part 77 approach surfaces or within the DCA DNL 65+ noise contour is subject to height limits (typically 25-35 feet depending on distance from DCA — detached AD maximum height of 20 feet under Section 12.9 is well within Part 77 limits on almost all Arlington parcels but should be verified for South Arlington parcels within the Runway 01 approach surface), and noise attenuation requirements for residential construction in DNL 65+ areas (additional insulation, acoustical glazing, STC-rated walls per the Uniform Statewide Building Code). Unlike Fairfax's Dulles-area noise contours, DCA's noise impact on Arlington is dominated by single-event overflight noise rather than DNL-averaged impact, so AD owners in South Arlington should expect frequent overhead noise even when nominally outside the DNL 65 contour. Owners in Aurora Highlands, Long Branch Creek, Crystal City residential, Alcova Heights, Pentagon City residential, and lower Arlington Ridge should verify Part 77 surface status via the FAA's 7460-1 obstruction evaluation tool before detached AD design; projects clearly within 20 feet of grade rarely trigger notification but projects at the 20-foot maximum on parcels near the airport sometimes do.
• Local Historic Districts (LHDs) under ACZO Section 11.3 and Chapter 31.1 of the County Code — HALRB review — An Accessory Dwelling on a parcel within a locally-designated LHD requires a Certificate of Appropriateness from the HALRB before the Zoning Administrator can issue the AD approval under Section 12.9. HALRB review typically adds 60-120 days to the overall AD timeline. The HALRB is particularly protective of street-facing elevations, roof forms, porch and entry details, and material authenticity; interior Accessory Dwellings not visible from the street are typically approved readily, while detached Accessory Dwellings visible from a public right-of-way often require significant design iteration. Maywood is the largest single-family LHD and sees the most AD review traffic; the garden-apartment LHDs (Buckingham, Colonial Village, Westover) rarely see single-family AD applications because the underlying parcels are multi-family apartment ownership. Parcels that are individually National Register-listed but not in an LHD are not subject to local HALRB review for AD additions. HALRB design guidelines for each LHD are published on the Historic Preservation Program page; owners contemplating an AD in an LHD should review the specific design guidelines and conduct a pre-application consultation with HALRB staff before engaging an architect.