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ADU Programs & Resources

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CA Dept of Housing and Community Development

What are ADUs?

photo of house

Accessory Dwelling Units (ADUs) are known by many names: granny flats, in-law units, backyard cottages, second units and more. No matter what you call them, ADUs are an affordable and compact option for adding much-needed housing in California.

What are the benefits of ADUs?

ADUs have many benefits including being:

  • an affordable type of home to construct in California because they do not require paying for land, major new infrastructure, structured parking, or elevators and even impact fees, in some cases.
  • a source of income for homeowners.
  • cost-effective wood frame construction, which is significantly less costly than homes in new multifamily infill buildings.
  • spacious enough to allow as much living space as many newly-built apartments and condominiums, and well-suited for couples, small families, friends, young people, and seniors.
  • a means to allow homeowners the flexibility to share independent living areas with extended family members or caregivers, which additionally allow seniors to age in place when they require more care.

Technical Assistance Booklet

ADU Technical Assistance Booklet

Download entire booklet(PDF)

Information for cities, counties, other local government bodies, and homeowners interested in adding an accessory dwelling unit to their property.

Download the entire booklet(PDF) or select one of the following excerpts:

Housing Trust Silicon Valley Small Homes, Big Impact Accessory Dwelling Unit (ADU) Program

Small Homes, Big Impact is a new pilot program from Housing Trust offering free educational workshops and financial assistance to homeowners seeking to build a secondary dwelling – commonly known as an accessory dwelling unit (ADU) – in their backyard.

Click here for an hour-long highlight video of the HTSV ADU Workshop led by local ADU practitioners (land use consultants, builders, design professionals, architects, lenders etc.) -- a teaser to the free, full-day, live ADU Workshop.

The workshops intend to answer the following five questions:

  1. Can I build an ADU on my site?
  2. How do I get a permit to build an ADU?
  3. How do I hire a builder and manage construction?
  4. How do I pay for an ADU?
  5. I’m a landlord, now what?

The workshops are led by local ADU Practitioners (land use consultants, builders, designers, architects, lenders etc.) during a half day course, typically on a Saturday.

The financial assistance program is currently being developed, it will consist of a planning grant and a construction loan. Products will be available in early 2019, register for more information.

Home for All: San Mateo County Resource Center

Second units, backyard cottages, garage apartments, ADUs, or granny flats – no matter what you call them, it’s now easier than ever to build them in San Mateo County.  Visit the Second Unit Resource Center for ideas/stories/photos, information on how to build an ADU, and don't forget to checkout the Second Unit Calculator to see typical costs and rents.