Accessory Dwelling Units (ADUs) in California have size restrictions that vary by type of ADU, location, and whether it's attached to a main residence. 

Attached ADUs

  • The maximum size is 50% of the main residence's living area, or 800 square feet, whichever is less 
  • Height limitations vary by local ordinance, but the maximum is 24 feet 

Detached ADUs

  • The maximum size is 800 square feet, unless the city or county has stricter requirements 
  • The ADU must be less than 16 feet high and have 4-foot rear and side yard setbacks 

Junior Accessory Dwelling Units (JADUs)

  • The maximum size is 500 square feet 
  • JADUs can be built within the walls of an existing or proposed single-family home 

Other restrictions 

  • The minimum size for an ADU is 150 square feet
  • The minimum dimension of any habitable room is 7 feet in any horizontal direction
  • The minimum ceiling height must comply with the California Residential Code
  • Cities and counties can also implement other restrictions, such as maximum lot coverage, minimum lot size, and open space requirements

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