ADUs are allowed in HerndonTypes:DetachedInternal
Types:DetachedInternal
Accessory Dwelling Unit (ADU) Rules for Herndon, VA
Is your property eligible for an ADU?
# of Properties
6,698
Owner-occupied
72%
Zoning districts
24
Avg Home Value
$747,772
Median Lot Size
0.22 acres
Avg Income
$158,194
Residential Types:
6,698 housing units
Single Family
47%
Apts (4+ units)
1%
Other
52%
Zoning Districts:
7,346 parcels · 24 districts
R-10
28%(2,065)
RTC
18%(1,356)
PD-R
18%(1,356)
PD-W
8%(574)
Other
27%(1,995)
ADU Rules
What can you build in Herndon, VA?
Herndon, VA follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.
Eligibility
- –Internal / Attached ADU: By Right
- –Detached ADU: By Right
Interior / Attached ADU Size Limits
- –Maximum size of 1,200 sq ft for internal or attached ADUs
- –Maximum size of 40% of the principal dwelling’s gross floor area for internal or attached ADUs
Detached ADU Size Limits
- –Maximum detached ADU size of 900 sq ft.
- –Total floor area of all detached accessory structures, including the ADU, may not exceed 50% of the principal structure’s floor area; the ADU alone cannot exceed this amount.
Max Units
- –1 ADU per lot
Owner Occupancy
- –Owner must occupy either the principal dwelling or ADU
Parking
- –1 space/ADU; off-street with convenient access to a street; in addition to the principal dwelling's required parking; no ADU waivers or transit-related reductions
Rental Restrictions
- –Short-term rentals prohibited in ADUs.
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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ADU rules in other Virginia municipalities
Rules change at the town line. Check the municipality your property is actually in.
Fairfax County