Secondary Units easier than ever to build

Amid a widespread housing shortage that is driving up rents and property values, the state has been forced to consider alternatives and one way is by revising its rules on Accessory Dwelling Units, or ADUs. And now it’s easier than ever to build one.

So what are ADUs, one might ask. People refer to these in a variety of terms including granny flats, in-law units, backyard cottages or secondary units. 

ADUs are a huge benefit to a homeowner because they offer an affordable way for a homeowner to receive an additional source of income without costing a ton of money. These ADUs are often constructed using cost-effective wood frame-construction without the high costs of homes that might require infill buildings, high costs of land or new infrastructure. 

These units offer spacious living spaces for couples, small families, friends and seniors and according to the state DOH (Department of Housing), providing the state with “an innovative, affordable, effective option for adding much-needed housing in California.” 

So, how is the DOH making it easier for homeowners to build these units? 

Two separate bills – SB229 and AB494 provide clarification and fee assistance for ADUs. 

These bills include provisions to laws that promote the development of ADUs, including:

  • Allowing for these units to be built concurrently with a single-family home. 

  • Opening areas where ADUs can be built, include all zoning districts that allow single-family homes

  • Modifying fees from utilities (special districts, water corporations, etc.)

  • Changes to parking requirements

  • Temporary amnesty over existing unpermitted units.  

So, how to get started? First stop should be at the San Mateo County’s Second Unit Center’s handy calculator page at to find out construction costs, income after expenses, property value increase and your return on investment. Next, visit your specific city to see its provisions, as each city has specific requirements for ADUs. 

For more information on your city’s particular guidelines:



San Mateo:

San Carlos:

Redwood City:

ADUs are a unique opportunity to address a variety of housing needs and provide an affordable housing option. California’s ADU reform laws are encouraging people to build safer, better ADUs, which might be an option for you too.