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

01 permits one accessory dwelling with any single-family dwelling, subject to three conditions. First, the floor area of the accessory dwelling cannot exceed 25% of the gross floor area of the primary residential structure on the lot, or a minimum of 500 square feet, whichever is greater; that floor gives smaller principal homes room for a legitimately sized accessory unit while capping larger ones as a share of the house they serve. Second, in the RP, R4 and R5 Zoning Districts (the county's higher-density residential districts), an accessory dwelling is only allowed if it is attached to the primary residential structure; a freestanding garage apartment or cottage is not permitted there.

Third, a manufactured home can never serve as the accessory dwelling in the RP, R4 or R5 Districts, regardless of size. Outside those three districts, including the county's RA Rural Areas district, an accessory dwelling may be detached from the main house. The same section separately allows one accessory dwelling tied to a business or industrial use, but only so long as it is occupied by the owner of the business or industry, an employee, or a watchman, tying that housing directly to the commercial operation it sits with. 01 set the zoning ceiling, not a standalone permitting path.