Fairfax, VA Accessory Structures: ADU Rules (2026)

The City of Fairfax is an independent city separate from Fairfax County, with its own Zoning Ordinance adopted under Virginia Code §15.2-2280, which authorizes localities to regulate the size, height, area, and location of buildings and uses. The City's Zoning Ordinance, most recently amended September 24, 2024, addresses Accessory Dwelling Units in §3.5.5.D.1. Under current standards, ADUs are permitted only as attached units located within an existing single-family home (e.g., basement apartments or interior conversions). The ADU must not exceed 35% of the principal dwelling unit's size and may contain no more than two bedrooms. Owner occupancy is mandatory: either the principal dwelling or the accessory unit must be occupied by the property owner. Detached ADUs (free-standing structures in the yard) are not currently permitted within City limits. The City Council and Planning Commission held an October 2025 work session directing staff to draft an ordinance to potentially permit detached ADUs, with follow-up Planning Commission and City Council work sessions scheduled for Spring 2026 to review setbacks, height, and design standards. ADU permits are administered by the Zoning Division of Community Development and Planning under the Administrative Regulations for the City of Fairfax. Importantly, short-term rentals (such as Airbnb) are prohibited city-wide, so an ADU cannot lawfully be operated as a short-term rental.