ADU rules in Fairfax County, VA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Fairfax County permits Accessory Living Units (ALUs) under Zoning Ordinance Section 4102.7. Interior ALUs (within the principal dwelling) may be approved by administrative permit; detached ALUs require a Special Permit from the Board of Zoning Appeals and a minimum 2-acre lot. Owner-occupancy of either the principal dwelling or the ALU is mandatory.
An ALU is permitted only in association with a single-family detached dwelling, and only one ALU is allowed per lot. Per Sect. 4102.7.B(4)(a), interior ALUs are limited to 800 sq ft of gross floor area or 40% of the principal dwelling, whichever is less. Detached ALUs (Sect. 4102.7.B(16)) may not exceed 1,200 sq ft and require a minimum 2-acre lot under Sect. 4102.7.B(15)(a). Occupancy is capped at two persons (Sect. 4102.7.B(7)). Either the principal dwelling or the ALU must be owner-occupied (Sect. 4102.7.B(6)); only one of the two units may be rented. Parking equals the principal dwelling requirement plus one additional space (Sect. 4102.7.B(9)). Virginia Code Sect. 15.2-2280 grants localities zoning authority over such uses. Application fee for the administrative permit is $270 with a $95 renewal fee.
Operating an ALU without the required administrative or special permit, exceeding the 800 sq ft / 40% interior cap or 1,200 sq ft detached cap, renting both the principal unit and ALU simultaneously, housing more than two occupants, or failing to maintain owner-occupancy can trigger a zoning violation notice from Fairfax County Code Compliance, fines, and revocation of the ALU permit.
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See how Fairfax County's adu rules rules stack up against other locations.
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