ADU Laws and Regulations

Rights Under State Law

  • ADUs are allowed in all residential zones and most commercial zones with limited exceptions for public safety, traffic, and water. For instance, the adequacy of water or sewer services.
  • State law says all homeowners in California are allowed to build an 800-square-foot freestanding ADU.
  • State law allows many types of existing spaces to be converted into ADUs. The state law covers garages, other accessory buildings (like art studios), or even part of the main house, including attics and basements.
  • Cities cannot charge impact fees—fees that pay for things like roads and parks— for ADUs under 750 square feet and must charge reduced fees for larger ones.
    • You will not need to add any parking for your ADU if it meets any of the following conditions:
      • A studio apartment
      • Within ½ mile of public transit
      • Within an existing structure (e.g., garage)
      • In a designated historic district
      • Within one block of car share locations

Fairfax Regulations

Local ADU and JADU regulations (for height, maximum square footage, floor area ratio, lot coverage, parking, etc.) for the Town are found in Chapter 17.048 of the Fairfax Municipal Code. Use the ADU Regulations Table below for guidance from Fairfax.

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