“ADU” stands for Accessory Dwelling Unit. These are secondary homes or apartments built on an existing single-family residential lot. Other names for ADUs include in-law units, granny flats, and backyard cottages. ADUs can be attached to a home or garage, or they can be a standalone unit. They typically range in size from 500 to 1,200 square feet and have their own kitchen, bathroom, living area, and a separate entrance.
ADUs are legal in California, and as of 2021, they’re now much simpler to build. Many of the previous restrictions on them have been lifted, and permits can be acquired in half the time (60 days instead of 120).
Anyone who owns a single-family home can build an ADU as long as their home is in a residential or mixed-use zone.
In Sonoma County, ADUs must be a minimum of 275 square feet and a maximum of 1,200 square feet. If the ADU will exceed your home’s floor-area ratio (FAR), the maximum size your ADU can be is 800 square feet.
The cost of an ADU varies depending on the project. You can use this accessory dwelling unit calculator to estimate your costs.
ADUs have the potential to increase the resale value of your property by approximately 20-35%. If you use your ADU as a rental, it will also generate monthly income.