Do ADU rules vary by Virginia county?

Yes — significantly. Until SB 531 takes effect on July 1, 2027, each locality sets its own size caps, occupancy rules, and whether detached ADUs are permitted. Always confirm with the local zoning department before design.

Will SB 531 override my county's ADU rules?

For by-right approval, permit-fee caps ($500), setback maximums and the family-relation requirement — yes. Localities keep control over building code, size, height and reasonable design standards.

Which Virginia counties are most ADU-friendly today?

Albemarle, Arlington, and the cities of Richmond and Alexandria are among the most ADU-friendly Virginia jurisdictions today. Fairfax and Prince William are more restrictive until SB 531 takes effect.

Are detached ADUs allowed in Arlington County?

Yes. Arlington has allowed detached accessory dwellings by administrative permit since 2019, making it one of Virginia's most established ADU jurisdictions.

How big can an Arlington ADU be?

Detached units are generally capped at about 750 square feet, or 35 percent of the combined floor area of the primary dwelling and ADU — whichever is less.

Do I have to live on-site to have an Arlington ADU?

Yes, owner-occupancy of the primary dwelling is currently required. SB 531 preempts that requirement on July 1, 2027.

County Rules

Virginia ADU rules, county by county.

A working snapshot of ADU rules across Virginia jurisdictions. Rules change constantly and localities differ. Always verify with the local zoning department before you design.

This table reflects rules as of publication. On July 1, 2027, SB 531 supersedes local restrictions where they conflict with the by-right ADU provisions. When in doubt, we'll confirm your county in a Readiness Assessment.

County / City	Detached ADU today	Size cap	Occupancy	Notes
Loudoun County	Allowed by-right today	Lesser of ~70% of main home or district cap	No family / owner-occ. requirement	Best-positioned county. Verify sewer/septic on rural AR-1 lots.
Fairfax County	Interior today; detached needs SUP + 2 acres	Interior ~800 sf / 40%; detached ~1,200 sf	Owner-occupancy required today	SB 531 makes detached by-right in 2027 and drops owner-occupancy.
Arlington County	Detached ADUs allowed by admin permit (since 2019)	~750 sf / 35% of combined floor area	Owner-occupancy required today	Lot coverage, tree preservation and parking often the constraints.
Prince William County	General ADUs NOT allowed today	N/A on standard SF lots	N/A today	SB 531 forces by-right ADUs county-wide in 2027 — biggest change on this list.
Fauquier County	One accessory dwelling per home in most districts	~800 sf (up to 1,000 sf on 5+ acres)	Varies by district	Health-department septic approval is the pacing item.
Albemarle County	Interior only today; detached prohibited	Interior capped at 35% of GFA	Owner-occupancy required today	SB 531 requires detached by-right and drops owner-occ. in 2027.

Loudoun County Fairfax County Arlington County Prince William County Fauquier County Albemarle County

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