ADU Pass
Chantilly
No County portion
Also in: Fairfax County · Loudoun County
ADU Pass helps homeowners in Chantilly, No County, Virginia navigate the permit paperwork for building an accessory dwelling unit. This area covers 1 ZIP code.
Map
ADU details
ADU legality: allowed-with-restrictions
Chantilly is a Fairfax-County CDP in the Dulles defense/intelligence corridor (~24,301 in 2020 census, down from a larger 2000 footprint after Greenbriar split off as a separate CDP). For Fairfax-County parcels, ADUs are permitted as interior ALUs only; detached units are not allowed county-wide. Some Chantilly western parcels are in Loudoun County and follow Loudoun's more flexible ADU framework.
Cost scenarios
| Scenario | Sq ft | Permit | Build | Total |
|---|---|---|---|---|
| minimum | 400 | $2,300 | $164,000 | $166,300 |
| 600 | 600 | $2,400 | $258,000 | $260,400 |
| midpoint | 700 | $2,500 | $308,000 | $310,500 |
| 1000 | 1,000 | $2,500 | $450,000 | $452,500 |
| maximum | 1,200 | $2,600 | $552,000 | $554,600 |
Fee breakdown (as of 2026-05)
Permitting process
Viability (permitted uses)
- Long-term rental: yes Long-term ALU rental permitted; landlord-tenant law and the ALU administrative-permit terms apply.
- Short-term rental: with-restrictions Fairfax County short-term-lodging permit required; STR permitted only by the owner-occupant. Proximity to Dulles airport makes STR economics attractive but compliance is strict.
- Office rental: no ALU must remain a dwelling unit; rental to a non-residential office tenant is not a permitted accessory use.
- Home office: yes Owner home occupation permitted subject to Fairfax home-occupation standards.
- Studio / workshop: yes Personal artist or workshop use by the owner-occupant permitted.
- Agriculture: no Chantilly is dense suburban; agricultural uses are very limited on residential parcels.
- Relative support: yes Family-occupancy ALU is the dominant Chantilly use case; multigenerational households are common given high housing costs and large Asian-Pacific and South-Asian populations.
Contacts
Utilities
- Water: Fairfax Water (most parcels) or Loudoun Water (western edge) · 21d connect · $5,500
- Sewer: Fairfax County Wastewater Management or Loudoun Water · 21d connect · $6,500
- Electric: Dominion Energy Virginia · 21d connect · $1,900
- Gas: Washington Gas · 28d connect · $1,700
Property values & taxes
Construction timeline
Realistic total: best 7mo · typical 11mo · worst 16mo
Modular pathway inspectors are novice with modular
Not commonly used for interior ALU work in Fairfax.
Financing
State ADU loans:
Insurance impact
HOA prevalence & preemption
Chantilly is heavily subdivided into HOA communities (Franklin Farm partly, Hunters Run, Greenbriar-adjacent, Pleasant Valley estates). Many HOA covenants restrict accessory dwellings or short-term lodging; check covenants before applying.
Regulatory overlays (2)
- airport-noise-zone
Chantilly sits directly south of Washington Dulles International Airport. FAA Part 150 noise contours cover significant areas; required disclosure on real-estate transactions. Loudoun and Fairfax both enforce Dulles overlay standards. - other
Westfields International Corporate Center covenant restrictions limit residential use on commercially-zoned parcels.
Technical envelope (climate & building code)
Climate & energy code
Building code
Amendments:
- Amendment
Contractor market (aggregate)
Legal history (timeline)
Current ordinance: Fairfax County Zoning Ordinance Chapter 112.2 - Accessory Living Unit provisions, adopted 2021-03-01, last amended 2024-01-01
- 2021-03-01 — Fairfax County Zoning Ordinance Modernization (zMOD) effective (county-ordinance)
Comprehensive rewrite of the Fairfax County Zoning Ordinance to Chapter 112.2; ALU provisions consolidated and modernized but kept the interior-only restriction county-wide.
Effect: Reorganized ADU/ALU rules; preserved the prohibition on detached accessory dwellings in Fairfax County. - 2023-09-26 — Fairfax County Zoning Ordinance Amendment ZO 112.2-2023-1 (county-ordinance)
Amendment effective 2024-01-01; primarily addressed off-street parking standards in Article 6 of the Zoning Ordinance.
Effect: Parking-related cleanups; does not expand ALU detached eligibility in Chantilly.
Known issues (2)
- policy-review — Fairfax County's ongoing public consultation on detached ADUs (Engage Fairfax) could change Chantilly's options; no regulatory change yet.
- other — Some Chantilly parcels straddle the Fairfax/Loudoun county line - jurisdictional confusion in permitting requires careful parcel verification.
County: no attribution (synthetic bucket)
No county
This city sits in the state's "no county" bucket — its ADU rules derive directly from state law and city ordinance without a county intermediary. No county-level sections apply.
Virginia state — ADU law and programs
State ADU law
Virginia has NOT enacted a statewide ADU preemption law. Virginia is a Dillon Rule state — localities possess only those powers expressly granted by the General Assembly — and the statutes granting zoning authority (Va. Code § 15.2-2280 et seq.) leave ADU regulation to local ordinances. ADU permission, setbacks, parking, size, and owner-occupancy rules therefore vary by county, independent city, and town. Virginia is unique in that it has 38 independent cities that function as counties (neither in nor subordinate to the surrounding county), meaning 'the county' for any given Virginia property may be an independent city rather than a true county. Several ADU preemption bills have been introduced in recent General Assembly sessions (2022 through 2025) without enactment; none have advanced past committee as of the Assembly's 2026 regular session adjournment.
State financing programs
Virginia does not operate an ADU-specific statewide loan, grant, or forgivable-loan program. Virginia Housing (formerly the Virginia Housing Development Authority, VHDA — rebranded 2020) administers general first-time-homebuyer, down-payment-assistance (DPA), mortgage-credit-certificate, and rehabilitation products that can be applied to ADU-adjacent purchases or improvements when eligibility criteria are met, but none target ADU construction as a distinct product. The Virginia Department of Housing and Community Development (DHCD) administers federal HOME and CDBG pass-through funds that local jurisdictions can direct toward ADU-adjacent rehab, but there is no state-level ADU-dedicated line item. Federally available products (FHA 203(k), Fannie Mae HomeReady and HomeStyle Renovation, Freddie Mac CHOICERenovation) remain the primary ADU financing path for Virginia homeowners.
State housing programs
Virginia does not run a state-level pre-approved-ADU-plan catalog, statewide impact-fee-waiver statute for ADUs, or streamlined-review mandate. State-level programs that touch ADU-adjacent policy are coordinated primarily through the Department of Housing and Community Development (DHCD) and Virginia Housing, and act by funding or assisting local jurisdictions rather than by preemption. Local ADU activity — Arlington County's Accessory Dwellings program (detached ADUs permitted since 2008, liberalized 2020), Alexandria's accessory-dwelling ordinance, Fairfax County's accessory-living-unit program, and Charlottesville's 2021 zoning-code changes — is authorized under the localities' Va. Code § 15.2-2280 zoning authority, not by state mandate.
- DHCD Community Development Block Grant (CDBG) Program — Federal CDBG funds administered by DHCD to eligible non-entitlement Virginia localities for community-revitalization, housing-rehab, and infrastructure projects. Not ADU-specific. Participating localities can direct CDBG funds toward housing-rehab projects where local policy supports ADUs.
- DHCD HOME Investment Partnerships Program — Federal HOME funds administered by DHCD to Virginia participating jurisdictions and non-profits for affordable-housing acquisition, rehab, and new construction. Not ADU-specific; can be directed to ADU-adjacent rehab at local discretion.
- Virginia Housing Commission — Permanent advisory commission of the General Assembly that studies housing-policy questions and recommends legislation. Has periodically studied ADU preemption and missing-middle housing without recommending statewide enactment as of 2026-04-21.
- Local ADU ordinances under Va. Code § 15.2-2280 authority — Not a state program — listed here because Virginia ADU policy is executed entirely at the locality level under the § 15.2-2280 zoning grant. A homeowner seeking to build an ADU consults the zoning ordinance of the specific county, city, or town where the parcel is located.
Federal (United States) — ADU-relevant rules and programs
Federal ADU law
The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.
Federal financing programs
Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.
Federal tax credits
There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.
Federal housing programs
HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.
ZIP Code
- 20153
Post Office
- 4410 Brookfield Corporate Dr, 20151