Learn more about ADUs

ADUs are being embraced throughout the Country as a way to increase housing, especially in single-family neighborhoods. As such, there are a variety of resources about ADUs and the ADU development process, and most cities and Counties have either their own resources or can direct you to places that do. 

For Homeowners in San Mateo County 

The County’s Second Unit Resources Center is a program created by its Home for All Initiative to provide information and tools to make it easier for homeowners to build second units and to help increase the housing supply in the County. It offers homeowner builders valuable information to navigate the entire process and challenges of building an ADU including:

  • An online calculator to estimate the cost and potential rental revenue of an ADU by San Mateo County jurisdiction;
  • the Second Unit Design Idea Book that provides readers with inspiration and information about ADUs that have already been built in San Mateo County; and
  • the Second Unit Workbook that explains the ADU development process from start to finish.

21 Elements is a great resource for ADU information and tools. It was created by the San Mateo County Department of Housing (DOH) and the City/County Association of Governments of San Mateo County (C/CAG). It is a collaborative planning project that helps all the 21 jurisdictions in San Mateo County address their housing needs and assists them with everything from RHNA to inclusionary housing to ADUs.

Homeowners outside of San Mateo County

Homeowners outside of San Mateo County can still benefit from the information provided to the left, but can also go to the California Department of Housing and Community Development’s (HCD) ADU website as well as AccessoryDwellings.org and BuildinganADU.com, all of which have great general tools and information.

For Older Adults or Homeowners Thinking About Aging-in-Place 

AARP created a Future of Housing Initiative to develop strategies to address the housing challenges for seniors and their families. They also created two ADU workbooks: a general guide and a step-by-step guide to design and development.

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