Sonoma County granny unit

Guest House vs. Granny Unit/Second Dwelling (updated for ADU)

Sonoma County zoning regulations for guest houses and second dwelling units define two distinct dwelling types:

  • A guest house is smaller and has no kitchen.
  • An ADU is a secondary dwelling unit with complete independent living facilities for one or more persons
    and generally takes three forms:
    ? Detached: The unit is separated from the primary structure
    ? Attached: The unit is attached to the primary structure
    ? Repurposed Existing Space: Space (e.g., master bedroom) within the primary residence is
    converted into an independent living unit
    ? Junior Accessory Dwelling Units: Similar to repurposed space with various streamlining measures

Guest House:

  • The floor area of a guest house shall be a maximum of six hundred forty (640) square feet.
  • No provisions for appliances or fixtures for the storage and/or preparation of food…
  • Shall not be located more than one hundred feet (100?) from the primary dwelling on the subject lot


  • An ADU shall not exceed 1200 square feet in floor area or exceed 50% of the main residente.
  • An ADU may be attached or detached from the primary dwelling on the site. A detached second dwelling unit may also be a manufactured home on a permanent foundation.

There are many qualifications and limitations that apply to both dwelling types, and you will need to check the Sonoma County Zoning Regulations for changes to the rules. Please keep in mind that many of the most recent changes have been mandated by the state. Too many municipalities and counties were making it impractical or too expensive to develop these smaller dwelling units that can address the housing crisis and provide extra income for homeowners with more space than they need. The new rules are still being formulated.