Loudoun County, VA Accessory Structures: ADU Rules (2026)

01 of the Zoning Ordinance governs accessory dwellings across the Agricultural Rural, Suburban, Transition, Transitional Residential, and Urban Employment districts (the unincorporated county; Leesburg, Purcellville, Hamilton, Middleburg, Round Hill, Hillsboro and Lovettsville set their own rules). Maximum size varies by district family: in the Transition, Rural (AR-1/AR-2), and Joint Land Management Area districts, an accessory dwelling can't exceed the lesser of 70% of the principal structure's gross floor area and footprint, or 2,500 square feet; in the Urban districts the same 70% test applies but the cap drops to 1,200 square feet; in the Suburban districts the footprint is capped at 50% of the principal structure's footprint and the floor area at the lesser of 50% of the principal structure's gross floor area or 1,200 square feet.

Only 1 accessory dwelling is permitted on a lot under 20 acres. A second is allowed once a parcel reaches 20 acres, and in the AR-1 and AR-2 districts specifically, one additional unit is permitted for every 25 acres beyond that 20-acre threshold; anything more requires a Special Exception. Accessory dwellings don't count toward density calculations and may sit inside a separate accessory building or within the principal structure itself. Placement rules differ by location: an attached unit follows the yard requirements of whatever structure it's inside, but a detached unit in an accessory building can come as close as 5 feet to side and rear lot lines provided the encroaching wall has no windows or doors.

In the PD-RV Village Center's Commercial and Workplace Areas, accessory dwellings must sit above the ground floor, and in AR Cluster Subdivisions they're allowed on Residential Cluster, Preservation Farm, and Rural Economy Cluster lots but barred from Common Open Space lots.