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Local ADU Rules

Fairfax

Last Updated May 21, 2025

ADU Contact:

Jeff Beiswenger jbeiswenger@townoffairfax.org

Standards	Details
Zones allowed	All residential and mixed-use zones with limited exceptions.
Lot Restrictions	Lot Coverage: can be considered if ADU is more than 800 square feet Restrictions: No closer than 20 feet to top of streambank
Minimum Lot Size	None.
Min/Max ADU Size	Minimum: 150 square feet Maximum: 850 square feet for studio/one bedroom 1000 square feet for more than one bedroom JADUs Maximum: 500 square feet One ADU and one JADU allowed on each single-family property. Also allowed on multifamily properties under state law. Maximum of 2 bedrooms.
ADU Building Height	Up to 16 feet and one story or detached. No greater than height of primary residence if attached.
Setbacks	None for conversions of existing living area or structure. 4-foot side and rear setbacks for new construction per State law and 10-foot front setbacks. Side and rear setbacks must meet fire safety requirements.
Parking Requirements	One parking space per ADU unless 1) within ½ mile of transit, historic district or car share, or 2) created by converting or demolishing garage or carport, then none required. Tandem parking and parking in setbacks are both allowed.
Owner Occupancy	Not required for ADU or primary residence. Required for JADU.
Sample fees from recent permits	ADUs: Application fee $141 Planning Fee $250 Use Permit (if required) $406.50 Building Permit (minor addition) $949.50 Building Permit (major addition) $1,400 JADUs: Application fee $62 Planning Fee $250 Building Permit $162 *Fees are specific to each project and will vary. Fees change regularly. These are provided as examples only.
Other requirements	Exterior Lighting: night sky compliant, shielded and 2 lumens max Fire Sprinklers: Needed if required for primary residence Floor Area Ratio (FAR): .40 FAR if ADU more than 800 sf Materials and Design: same as the primary dwelling unit Protected Trees: 2:1 replacement with 36-inch box trees Windows: Second-story windows facing side and rear of property must have minimum plate height of 6 feet above floor height unless set back more than 30 feet from property line.
Process	Complete applications reviewed by City within 60 days per State law. ADUs not defined in State Code, such as ADUs above a garage require Design Review Approval. Disclaimer: standards and process may vary. Consultation with the contact is recommended before starting any project.
Exceptions	None.

Wondering what you can build?

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