Fairfax County

All ALU permitting in unincorporated Fairfax County is handled by the Department of Planning and Development (DPD, zoning / ALU application review) in coordination with Land Development Services (LDS, building permits, site plans, inspections). The three incorporated towns (Herndon, Vienna, Clifton) and the two adjacent independent cities (City of Fairfax, City of Falls Church) operate their own permitting offices and are NOT served by the county process; residents of those jurisdictions must apply through their municipal building / zoning offices. For all other Fairfax County parcels, ALU approval follows one of two tracks based on the ALU type: (a) Administrative ALU (interior, contained within existing primary-dwelling footprint, meeting all Section 8102 standards by right) — submitted to the DPD Zoning Administrator, reviewed administratively without public hearing, typically approved in 30 to 60 days, followed by a separate LDS building permit for any interior alterations and a DPD zoning sign-off; (b) Special Permit ALU (detached accessory structure or exterior alterations beyond Administrative thresholds) — submitted to the DPD Zoning Administrator, noticed to adjacent property owners per Va. Code Section 15.2-2204 and the Fairfax County procedures, heard at a public hearing by the Board of Zoning Appeals (BZA), typically decided within 4-6 months of complete application. Both pathways culminate in LDS-issued building / trade permits (electrical, plumbing, mechanical) under the Virginia Uniform Statewide Building Code, LDS inspections (footing, framing, rough-ins, final), and a Certificate of Occupancy. Parcels served by public water and sewer (most of the county east of the Fairfax County Parkway) use Fairfax Water and the Fairfax County Department of Public Works and Environmental Services (DPWES) Wastewater Management; parcels on private well and septic (concentrated in western Fairfax, including much of the Great Falls, Clifton, and Fairfax Station areas) require Fairfax County Health Department review of septic capacity.

Process overview: ALU approval in Fairfax County follows: (a) applicant reviews the ALU standards at Section 8102 and the county ALU guidance page to determine whether the proposed unit qualifies for the Administrative ALU path (interior, within existing footprint, meets all standards by right) or requires a Special Permit ALU (detached accessory structure, exterior alterations beyond Administrative thresholds); (b) for Administrative ALUs, applicant submits through PLUS with a site plan showing primary dwelling and ALU location, floor plans demonstrating compliance with 1,200 sqft / 40%-of-principal size cap, separate-entry and separate-kitchen demonstration, parking-space calculation, and a signed owner-occupancy affidavit; DPD Zoning Administration reviews for Section 8102 compliance and issues Administrative ALU approval typically within 30-60 days; (c) for Special Permit ALUs, applicant submits through PLUS with the Special Permit application package, including site plan, floor plans, elevations for the detached unit, statement of justification, adjacent-property owner list for mailed notice, and the Special Permit application fee; DPD prepares a staff report, notices the application per Va. Code Section 15.2-2204 requirements (mailed notice to adjacent owners, newspaper legal notice, site posting 15 days before hearing), and schedules a BZA public hearing; BZA hears the case, receives public comment, and either grants (typically with conditions), denies, or defers the Special Permit — typical timeline is 4-6 months from complete application to BZA decision; (d) once ALU approval is in hand (Administrative or Special Permit), applicant submits building permit through PLUS to LDS with construction documents sealed by a Virginia-licensed architect or engineer for any structural work; LDS plan review covers structural, electrical, plumbing, mechanical, and energy-code requirements under the 2021 Virginia Uniform Statewide Building Code; (e) for parcels on private well and septic (common in Great Falls, Clifton, Fairfax Station, and rural portions of Sully and Mount Vernon districts), Fairfax County Health Department evaluates whether the existing septic system has capacity for the ALU's added occupancy and flow, or requires an upgraded system; (f) LDS issues building and trade permits; (g) construction with LDS inspections (footing, slab, framing, rough-in electrical / plumbing / mechanical, insulation, final); (h) Certificate of Occupancy issued by LDS on final inspection pass. For parcels in Chesapeake Bay Preservation Act Resource Protection Areas, in FEMA Special Flood Hazard Areas, or in the historic overlay districts, parallel sub-reviews add specific procedural steps and typically add 30-90 days to the total timeline.

Impact fees: Virginia counties have narrow statutory authority to charge development impact fees (Va. Code Section 15.2-2317 et seq., with most fee authority limited to roads and requiring specific Board of Supervisors adoption and formula-driven computation). Fairfax County does impose a transportation impact fee in certain districts and service-connection fees through Fairfax Water and DPWES Wastewater, but does NOT charge a California-style per-square-foot impact fee schedule on ALUs. The core costs of an ALU permit in Fairfax County are (i) the zoning application fee — approximately $500-$700 for an Administrative ALU and approximately $2,500-$5,000+ for a Special Permit ALU (plus required BZA advertising costs, typically several hundred dollars for newspaper legal notice and mailed notices); (ii) LDS building permit fees under the adopted fee schedule, which are cost-recovery based and scale with construction valuation (a typical ALU with $100,000-$200,000 in valuation incurs several thousand dollars in building-permit fees); (iii) trade permit fees for electrical, plumbing, and mechanical work; (iv) Fairfax Water connection / availability fees for parcels on public water; (v) DPWES Wastewater availability fees for parcels on public sewer — ALU connections are typically handled as an addition to the primary-dwelling service rather than a separate connection, though a separate meter can be installed on owner request; (vi) Fairfax County Health Department septic evaluation / upgrade fees for private-septic parcels. School impact fees are not authorized for general locality use in Virginia; Fairfax County does not impose them on ALUs or any other residential construction. (schedule)

The Fairfax County Department of Tax Administration, Real Estate Division (commonly referred to as the county assessor) maintains parcel-level assessment records for all real property in the county (excluding the three incorporated towns and the two adjacent independent cities, which maintain their own assessment rolls). 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. Fairfax County reassesses real estate ANNUALLY under Va. Code Section 58.1-3253 — notices are mailed in late February each year showing assessed values as of January 1 of the tax year. An ALU 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 Fairfax reassesses annually, an ALU completed mid-year will appear on the next February's assessment notice. Virginia has no Prop 13 cap; the statewide real-estate-tax rate Fairfax sets applies to full fair market value (the 2024-2025 general district real estate tax rate was $1.125 per $100 assessed value; Fairfax also levies several special-district additions for transportation, stormwater, and commercial / industrial C&I districts). Fairfax's high median property values mean the annual tax impact of an ALU is larger in absolute dollars than in most other Virginia counties.

Assessment policy: Virginia Code Title 58.1 requires assessment at 100% fair market value. Fairfax County reassesses annually under Section 58.1-3253, with January 1 as the effective date and notices mailed in late February. For ALU additions, the assessor incorporates the new improvement into the next annual assessment cycle — there is no separate supplemental notice as in California. Typical Fairfax County ALU assessed-value increments for 700-1,200 sqft interior conversion or detached ALUs range from roughly $180,000 to $350,000 in the post-2024 market (reflecting Fairfax's very high median property values and construction costs in the Northern Virginia submarket), producing a property-tax increment of roughly $2,000 to $4,000+ per year at the $1.125 per $100 assessed value base rate (plus any applicable special district adders, which in the I-66 and Tysons area can add another $0.10-$0.15 per $100). The primary dwelling's assessed value is also revisited each year, so any market appreciation of the primary dwelling is captured alongside the ALU 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. Fairfax does publish market-sales data and neighborhood valuation-model reports each year in conjunction with the annual reassessment, giving owners visibility into how the mass-appraisal models are tuned.

Fairfax County administers several county- and state-level overlay regimes that materially affect ALU siting: (1) the Chesapeake Bay Preservation Act (CBPA) Resource Protection Area (RPA) and Resource Management Area (RMA) buffers, mandated by Va. Code Section 62.1-44.15:67 et seq. and administered locally through the Chesapeake Bay Preservation Ordinance (Chapter 118 of the Fairfax County Code) and the zoning ordinance — 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; (2) the Fairfax County Flood Plain Management Ordinance (Chapter 118-6 of the County Code and Article 4 Section 4102 of the zoning ordinance) covering FEMA Special Flood Hazard Areas along the Potomac River, Occoquan River, Bull Run, Pohick Creek, Accotink Creek, Little Hunting Creek, Cameron Run, Difficult Run, Sugarland Run, and their tributaries; (3) Historic Overlay Districts (HODs) governed by Article 7 Section 7102 of the zoning ordinance — the principal HODs are the Fairfax Courthouse HOD (around the historic 1800 Fairfax County Courthouse in the City of Fairfax area with county-jurisdictional portions immediately adjacent), the Clifton HOD (Town of Clifton's locally-designated historic district, which extends into unincorporated county parcels in the Clifton CDP), the Ash Grove HOD, the Colchester HOD, the Lake Barcroft HOD, the Lorton Historic District, and several Civil War battlefield overlays including the Historic Bull Run Battlefield area and Mount Vernon Historic District; (4) Airport Noise Contour Overlay Districts addressing airspace around Washington Dulles International Airport (IAD, operated by Metropolitan Washington Airports Authority), Reagan Washington National Airport (DCA) approach corridors, and Davison Army Airfield (KDAA) at Fort Belvoir — the Dulles airspace cuts across northwestern Fairfax including Herndon, Chantilly, and parts of Great Falls, while DCA approach corridors affect eastern Fairfax along the Potomac; (5) the Runway Protection Zone and Noise Impact Area around Davison AAF at Fort Belvoir in southeastern Fairfax; (6) Highway Corridor Overlay Districts (HCODs) along I-66, I-95, Route 7, Route 29, Route 28, and the Fairfax County Parkway, with architectural and setback controls that interact with exterior ALU design. 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 — Fairfax has no WUI overlay comparable to California's CAL FIRE VHFHSZ system.

• Chesapeake Bay Preservation Act Resource Protection Area (RPA) — 100-foot buffer — and Resource Management Area (RMA) — ALU designs that cantilever over, or place impervious surface within, the 100-foot RPA buffer require an RPA Exception. Fairfax's RPA Exception process involves a Water Quality Impact Assessment (WQIA), DPD Environmental Review, and in more impactful cases a Planning Commission review. Adding 60-120 days to the overall ALU timeline for an RPA Exception is typical. Owners with parcels along Difficult Run (much of Great Falls, Oakton, and Vienna-area CDPs), Accotink Creek (much of Fairfax Station, Burke, and Annandale area), Pohick Creek (western Lorton, Springfield), and the Potomac shore (Mount Vernon, Belle Haven, River Bend) should confirm RPA status via the Fairfax County RPA Map Viewer before design.
• Fairfax County Flood Plain Management Ordinance — FEMA NFIP participant — ALUs in an SFHA must have lowest floor elevated to or above Base Flood Elevation plus Fairfax'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. The substantial-improvement trigger (Section 4102 >50% of structure value over any 10-year lookback) is cumulative — multiple smaller renovations can aggregate to trigger full floodplain compliance for the whole structure. Owners along the Potomac, Difficult Run, Accotink Creek, Pohick Creek, and the Occoquan should verify current FIRM status (2023 effective panels plus LOMRs) via the county's Floodplain Viewer before ALU design. Flood insurance is federally required for SFHA parcels with federally-backed mortgages.
• Airport noise and safety zones — Washington Dulles International (IAD), Reagan Washington National (DCA), and Davison Army Airfield (KDAA) at Fort Belvoir — ALU siting inside the 65+ DNL noise contour or within a Part 77 approach surface is subject to height limits (typically 35 feet for detached ALUs under the base zoning, lower within Part 77 approach surfaces), noise attenuation requirements for residential construction in DNL 65+ areas (additional insulation, acoustical glazing, STC-rated walls per the Uniform Statewide Building Code), and avigation easement recording for new residential construction. Owners in Chantilly near Dulles, in western Herndon, in Great Falls within Part 77 surfaces, along the Potomac in eastern Fairfax, or within the Davison AAF AICUZ footprint in Lorton should verify Airport Overlay and Part 77 status before a two-story detached ALU design. The MWAA has aggressive flight-track monitoring for Dulles overflights and the DCA noise complaint history is well-documented in MWAA annual reports.
• Historic Overlay Districts (HODs) under Zoning Ordinance Article 7 Section 7102 — An ALU on a parcel within a locally-designated HOD requires a Certificate of Appropriateness from the ARB before the Zoning Administrator can issue the ALU approval. ARB review typically adds 60-120 days to the overall ALU timeline. The ARB is particularly protective of street-facing elevations and roofline characteristics; interior Administrative ALUs (not visible from the street) are typically approved readily, while detached ALUs visible from a public right-of-way can require significant design iteration. Clifton's HOD is the most restrictive in practice due to the small parcel sizes and the district's intact 19th-century character. Parcels that are individually National Register-listed but not in an HOD are not subject to local ARB review for ALU additions.