ADU Pass
King William County
ADU Pass helps homeowners in King William County, Virginia navigate the permit paperwork for building an accessory dwelling unit. We cover 5 cities and 7 ZIP codes in this county.
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County ADU details
County ADU ordinance
King William County does NOT maintain a standalone accessory-dwelling-unit ordinance with dedicated definitional and dimensional standards. ADUs in King William County are regulated indirectly through the Zoning Ordinance's treatment of 'accessory use,' 'accessory structure,' and 'dwelling, single-family detached' in Article II, combined with the per-district use schedules. In the A-C Conservation, A-1 Agricultural Limited, and RC Rural Conservation districts (which cover the great majority of county acreage), one principal dwelling per lot is permitted with customary accessory structures; a second independent dwelling unit typically requires a Special Use Permit from the Board of Supervisors after Planning Commission recommendation, though a 'family-member' or 'tenant house / farm labor dwelling' allowance is recognized in the agricultural and rural-conservation districts subject to minimum lot area (commonly 10 acres) and agricultural-use demonstration. In the R-1 and R-2 residential districts, a second dwelling requires a Special Use Permit. A 'guest house' accessory structure without independent kitchen facilities (no cooking facilities) is generally permitted as a by-right accessory structure subject to district setback, height, and lot-coverage standards. Applicants should confirm current ordinance text with the Zoning Administrator before committing to a project pro forma — the ordinance has been amended multiple times and specific ADU-like allowances vary by district and by interpretation of the 'customarily incidental' accessory-use standard.
County permitting (unincorporated parcels)
King William County's Department of Community Development handles zoning permits, Special Use Permits, site plan review, and subdivision review for every parcel in the county except those inside the Town of West Point (which administers its own zoning) and parcels on the Mattaponi and Pamunkey reservations (tribal sovereignty). Building Inspections issues building permits and trade permits for the same non-tribal, non-town territory. A typical ADU-like permit bundle (where a second dwelling is permitted) includes: (1) a Special Use Permit from the Board of Supervisors with Planning Commission recommendation, unless the parcel qualifies for an agricultural / rural-conservation tenant or farm-labor dwelling allowance, (2) a Zoning Permit confirming use compliance and district setback compliance, (3) a Building Permit with stamped residential plans, (4) Electrical, Plumbing, and Mechanical trade permits, (5) a Virginia Department of Health (VDH) - Three Rivers Health District construction permit for well and/or septic on parcels not served by public water or sewer (which is the great majority of parcels in the county — only the Central Garage / Route 360 corridor and the Town of West Point area have material public utility coverage), (6) a Floodplain Development Permit if any portion of the parcel is within the mapped Special Flood Hazard Area along the Mattaponi or Pamunkey Rivers or their tributaries, (7) a Chesapeake Bay Preservation Act review — King William County IS a Tidewater locality subject to the CBPA, so Resource Protection Area (RPA) and Resource Management Area (RMA) rules apply across tidal-water-adjacent parcels, and (8) a Historic District review if the parcel is within a county-designated historic overlay.
County assessor
King William County real estate is assessed by the Office of the Commissioner of the Revenue working with the Real Estate Assessment Office. King William County operates on a periodic general-reassessment cycle under Va. Code § 58.1-3252; the county historically uses a four-year cycle with reassessments typically contracted to an outside assessment firm. An ADU or second-dwelling addition is captured through the supplemental real-estate-improvement process under Va. Code § 58.1-3292: the Commissioner of the Revenue receives the building-permit record and Certificate of Occupancy from Building Inspections, and the Real Estate Assessment Office adds the ADU's assessed value to the parcel's land and improvement base, prorated to the completion date. The primary dwelling is NOT re-valued off-cycle as a result of the ADU addition. Tribal trust land inside the Mattaponi and Pamunkey Reservations is not assessed by the county.
Assessment policy: An ADU is captured as a real-estate improvement under Va. Code Title 58.1 Subtitle III Chapter 32. On receipt of the building permit and (later) the Certificate of Occupancy from Building Inspections, the Real Estate Assessment Office prorates the supplemental assessment from the completion date through the end of the tax year under Va. Code § 58.1-3292. The ADU is added at its assessed fair-market value (typically derived from cost approach using Marshall & Swift residential cost multipliers calibrated to the current reassessment-cycle base) on top of the parcel's existing land and improvement value; the existing primary dwelling is NOT revalued off-cycle. There is no King-William-County-specific ADU assessment exemption. Standard Virginia real-estate tax relief programs (elderly and disabled relief under Va. Code § 58.1-3210 as adopted locally, disabled-veteran exemption under Va. Code § 58.1-3219.5) apply to the homeowner's principal residence and may extend to the parcel as a whole depending on local-option rules; they do not create a separate carve-out for the ADU itself. Tribal trust land on the Mattaponi and Pamunkey Reservations is not on the local real-estate tax rolls.
County overlays (5)
King William County administers several overlay regimes that bear materially on ADU projects: (1) a Floodplain Overlay District tied to FEMA Special Flood Hazard Areas along the Mattaponi River, the Pamunkey River, and their tributaries — King William County is a distinctly river-bounded Middle Peninsula jurisdiction and a substantial share of low-lying tidal-adjacent parcels are in-mapped floodplain; (2) Chesapeake Bay Preservation Act jurisdiction across the county (King William is a Tidewater locality designated under Va. Code § 62.1-44.15:67 et seq.), with Resource Protection Area (RPA) buffers of 100 feet from perennial water bodies and tidal wetlands and Resource Management Area (RMA) coverage across additional landward extent; (3) the Mattaponi Indian Reservation and the Pamunkey Indian Reservation, which are sovereign tribal enclaves outside county zoning and building-permit jurisdiction; (4) locally-adopted historic overlays and NRHP-listed rural corridors. King William County has NO California-style coastal commission (Virginia has no coastal-commission analog; coastal regulation flows through the CBPA, the Virginia Marine Resources Commission for tidal-wetlands permits, and local ordinances), NO CalFire-equivalent WUI regulatory overlay (Virginia has no statewide WUI overlay), and NO seismic-retrofit overlay.
- Floodplain Overlay District
- Chesapeake Bay Preservation Act (CBPA) Resource Protection Area and Resource Management Area
- Mattaponi Indian Reservation (sovereign tribal enclave)
- Pamunkey Indian Reservation (federally recognized sovereign tribal nation)
- King William County historic overlays and NRHP-listed rural corridors
Known county issues (5)
- other — ADU pro formas that would pencil as by-right or ministerial projects in jurisdictions with codified ADU ordinances require a discretionary SUP cycle in King William County. This adds roughly 90-150 days of wall-clock, a separate SUP application fee ($500-$1,500), neighbor-notification and public-hearing burdens, and case-by-case conditions imposed by the Board of Supervisors. Applicants should budget accordingly and should confirm whether an A-1 / RC tenant or farm-labor dwelling allowance or a no-kitchen 'guest house' accessory structure path can satisfy the use case without an SUP.
- other — On tidal-frontage and creek-frontage parcels, the CBPA RPA is often the binding constraint on ADU siting — more binding than the zoning ordinance's use rules. Applicants should (a) pull the county GIS to confirm RPA / RMA footprint before committing to a detached ADU, (b) budget 30-60 days for CBPA review where the project approaches the buffer, and (c) prepare a Water Quality Impact Assessment if encroachment is unavoidable. Exceptions to the RPA buffer for new residential structures are rarely granted.
- other — For tribal-land projects, applicants must work with the Mattaponi Tribal Council or the Pamunkey Tribal Government rather than with King William County. For fee-simple parcels adjacent to either reservation, ordinary county review applies, but reservation boundaries should be confirmed by survey before siting structures near the line, and tribal treaty rights (fishing, hunting along the respective rivers) should be respected in siting riparian accessory structures. The county parcel viewer and Commissioner of the Revenue records do not carry tribal-land parcels.
- other — VDH well-and-septic evaluation is a separate timeline from county permit review and has experienced episodic backlogs as post-pandemic permit volume rose against a stable VDH staffing baseline. Applicants should initiate VDH application in parallel with — not after — the county pre-application inquiry. Parcels with marginal soils for conventional septic may need alternative onsite-sewage (AOSS) design, which adds cost ($15k-$40k incremental over conventional) and a longer engineering-and-permit timeline.
- policy-review — Applicants should confirm the current ordinance text with the Zoning Administrator (804-769-4949) rather than relying on prior summaries, and should be alert to General Assembly session outcomes in any year when an ADU preemption bill is introduced. A pre-application zoning inquiry is strongly recommended before architectural or engineering investment — the Zoning Administrator's interpretation is frequently the difference between a by-right accessory-structure path and a full SUP cycle.
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.