Accessory Dwelling Units (ADUs) are commonly known as backyard cottages, secondary units, granny flats, or law units. As the name suggests, they are small dwelling units on single or multifamily residential, agricultural, or commercial properties.

Homeowners can have these backyard cottages attached or detached from their primary houses or other buildings within their properties. ADUs play a significant role in solving the shortage of affordable rental housing in Sonoma County.

Establishing an ADU may involve constructing a new structure, designating an existing accessory structure, or remodeling part of an existing structure. However, you must meet several zoning codes before establishing a dwelling unit. This post will focus on the size limits for Accessory Dwelling Units in Sonoma County.

 Sonoma County ADU Size Requirements

There are different Accessory Dwelling Units, each with varying size limitations in Sonoma County. They include attached accessory dwelling units, detached accessory dwelling units, and Junior accessory dwelling units.

  • Attached Dwelling Units– The minimum area for an attached ADU should be 150 sq. ft. The unit should not exceed 30% of the primary dwelling’s living space. The horizontal measurements of any habitable room (except the kitchen) should not be less than 7 feet.
  • Detached Accessory Dwelling Units– The detached ADU should not have a floor area less than 150 sq. ft, and the maximum size should not exceed 850 sq. ft. Detached ADUs occupying more than 650 square feet should not exceed more than 50% of the main dwelling’s living space.
  • Junior Accessory Dwelling Unit– Habitable rooms (except kitchens) should have a minimum size of 70 square feet, and the maximum floor area is 500 square feet.
  • Efficiency Dwelling Units- These units contain only one habitable room other than the kitchen. It is essential to note that bathrooms, halls, utility spaces, and closets are not habitable rooms. The floor area of an efficient dwelling unit should not be more than 500 sq. ft or less than 150 sq. ft.

Contact Homestar Building Performance Today

Do you want to earn some rental income, create additional space for your teenager, or boost the value of your home by establishing an accessory dwelling unit in Sonoma County? At Homestar Building Performance, we have more than two decades of experience building high-quality ADUs in Sonoma County.

We understand the area’s zoning requirements, so you can rest assured you won’t face trouble with the authorities when you work with us. Contact us online, or call us at (707) 849-9237 to learn more about how we can make your dream a reality.


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