Accessory Dwelling Units (ADUs)

Accessory dwelling units (ADUs) are also known as granny or in-law units.  In Cotati, nearly every residential property is eligible to construct an ADU. ADUs may also be placed on multifamily properties and in mixed-use zoning districts

ADUs can come in many shapes and sizes, but an ADU is always a self-contained home that is smaller than the primary residence and legally part of the same property. They generally fall into one of the following categories:

  • Detached: Free-standing structure, such as a backyard cottage
  • Attached: Shares at least one wall with the primary residence
  • Interior Conversion: Built from existing space in the primary residence (such as an attic or a basement)
  • Garage Conversion: Converted former garage space
  • Above Garage: Unit built above a garage (can be attached to or detached from primary residence)
Napa ADU
Accessory Dwelling Units Types

On lots of less than 1/2 acre in size, the maximum size allowed is 850 square feet for studio or 1 bedroom ADUs, and 1,000 square feet for 2+ bedroom ADUs. On lots of 1/2 acre or more, the maximum ADU size is 1,200 square feet. ADUs are subject to height and property line setback limitations as well. Refer to the ADU Standards summary for more information about development requirements.

In addition to an ADU, most single-family residential properties are also eligible to construct a Junior ADU (JADU) in addition to an ADU. JADUs are limited to 500 square feet and may only be located within the walls of an existing or proposed single-family residence. JADUs must include a separate entrance from the primary residence and an efficiency kitchen, but may share a bathroom with the primary residence.


Napa Sonoma ADU Center
Provides a wealth of resources for homeowners considering  an ADU or JADU. Explore their website to find useful resources such as designs and floor plans, an ADU Handbook, helpful webinars, an ADU calculator, and stories from people that have built ADUs.

Homes for Sonoma
Nonprofit developer creating quality workforce housing options that support a safe and sustainable community, with an emphasis on ADUs.