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ADUs are allowed in Unincorporated Fairfax
Types:DetachedInternal

Accessory Dwelling Unit (ADU) Rules for Unincorporated Fairfax, VA

Is your property eligible for an ADU?

# of Properties
309,060
Owner-occupied
83%
Zoning districts
66
Avg Home Value
$949,607
Median Lot Size
0.24 acres
Avg Income
$179,641
Residential Types:
309,060 housing units
Single Family
61%
Other
39%
Zoning Districts:
355,673 parcels · 66 districts
R-3
19%(68,939)
R-2
10%(37,075)
PRC
8%(29,272)
R-1
7%(26,463)
Other
55%(193,924)

ADU Rules

What can you build in Unincorporated Fairfax, VA?

Unincorporated Fairfax, VA follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.

Interior / Attached ADU Size Limits

  • –Maximum size is the lesser of 800 sq ft or 40% of the principal dwelling’s gross floor area.

Detached ADU Size Limits

  • –Maximum detached accessory dwelling size of 1,200 sq ft of gross floor area.

Max Units

  • –Single-family detached: 1 ADU per lot
  • –Single-family attached, duplex, multifamily: 0 per lot

Owner Occupancy

  • –Either the ADU or principal dwelling must be owner-occupied

Parking

  • –1 space/ADU (in addition to base 2 on public streets or 3 on private streets); no max; tandem parking allowed; Transit Station Areas: no ADU-specific reduction

Rental Restrictions

  • –Short-term lodging prohibited for ADUs with an ALU (detached or attached); no long-term rental ban stated.

ADU State Law

What can you build in Virginia?

  • –Virginia does not have a statewide ADU mandate; ADU rules are set by individual municipalities.
  • –Building/fire codes are set statewide, but whether an ADU is allowed is local zoning.
  • –SB 304 would have mandated ADUs. It passed the Virginia Senate in 2024 but was continued/left in House committee (i.e., not enacted statewide)

What's allowed on your lot?

These are the municipality-wide rules. What's allowed on a specific property also depends on state laws, setbacks, floor area ratio, lot coverage, environmental constraints, topography, and other property-specific factors. Search your address on FutureLot to see what's allowed on your property.

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Is your property eligible for an ADU?

ADU rules in other Virginia municipalities

Rules change at the town line. Check the municipality your property is actually in.

Fairfax County

HerndonVienna
See all municipalities in Fairfax County →See all Virginia municipalities →
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