Local Permitting Guide
Building an Accessory Dwelling Unit in the City of Fairfax
⚠ Important Notice
This page summarizes publicly available government information for general educational purposes only. HomeSprout LLC did not create this information, does not guarantee its accuracy, completeness, or currency, and is not responsible for decisions made based on it. Rules change and vary by property — always verify current requirements directly with the official source below before proceeding with a project.
Official source: City of Fairfax — Accessory Dwelling Units: What to Know
Does This Guide Apply to You?
This guide applies to the City of Fairfax — an independent city, entirely separate from Fairfax County despite sharing the name and serving as the county seat. If your address says "Fairfax" but you're actually in unincorporated Fairfax County, confirm your jurisdiction first — see our Fairfax County guide if that's you.
The City of Fairfax currently permits attached ADUs, and has been actively considering allowing detached ADUs as well. Here's what's confirmed as of this writing — for project-specific eligibility, always confirm directly with the City's Zoning Division.
Attached ADUs (Currently Permitted)
- Must be attached as part of the primary home — a complete, independent living unit with a separate kitchen, sleeping, and bathroom facilities
- Cannot exceed 35% of the total gross floor area of the principal dwelling
- Maximum of two bedrooms
- The property owner must occupy either the main home or the ADU
Detached ADUs (Under Active Consideration)
As of this writing, the City of Fairfax does not currently allow detached ADUs. City Council has been working through this specifically — Planning Commission and City Council work sessions in 2025 and 2026 discussed draft standards, with public hearings scheduled to formally consider an amendment. If a detached-ADU option matters to your project, check directly with the City's Zoning Division for the current status before assuming either way.
Permits Required
- Zoning Permit for Residential Accessory Use and Occupancy (City Zoning Office)
- Business License, if the ADU generates rental income
Worth knowing: short-term rentals (Airbnb-style) aren't allowed anywhere in the City of Fairfax, ADU or otherwise.
Not sure what applies to your property?
Zoning district and lot specifics affect what's actually buildable. We handle the zoning determination and permitting process as part of our design-build service.
Request a Consultation