5 county-level rules, plus city-specific rules for 3 cities in Fairfax County, Virginia.
Verified from official government sources
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.
Fairfax County Zoning Ordinance allows accessory sheds on residential lots, with setbacks and size limits varying by zone. Sheds 256 square feet or smaller and not on a permanent foundation are exempt from building permits under the Virginia USBC, but still must comply with zoning setbacks (typically 5–10 ft from side/rear property lines) and may not be placed in front yards.
Detached garages are allowed as accessory structures in all residential zones in Fairfax County, subject to setbacks (typically 5–10 ft from side/rear lines), height limits (15 ft or principal structure height), and lot coverage caps. Building permits are required. Detached garages may be converted to ALUs under the 2021 zMOD rules with additional permits. HOA architectural review typically required.
Fairfax County treats a carport as a freestanding accessory structure under the Zoning Ordinance (Chapter 112), Article 4 use rules and Article 5 dimensional standards. A building permit is required for any structure over 256 square feet. Setbacks vary by zoning district (Article 2). On lots 36,000 sq ft or less, freestanding accessory structures are not permitted in any front yard.
Fairfax County does not allow detached backyard tiny homes on most residential lots. The Zoning Ordinance treats a second dwelling as an Accessory Living Unit (ALU); interior ALUs require an administrative permit while detached ALUs require a special permit on lots of 2 acres or more. All construction must meet the Virginia Uniform Statewide Building Code (13VAC5-63).
3 cities in Fairfax County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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