What is an Accessory Dwelling Unit?

Accessory Dwelling Units (ADUs), sometimes called secondary units, granny units, in-law units, and backyard cottages, are self-contained residential units located on the same lot as, but separate from, the primary unit, with a separate entrance, kitchen, and bathroom. ADUs can be either attached or detached from the main dwelling, and are sited in a manner that preserves the single-family nature of a neighborhood. A junior ADU (JADU) is an ADU typically attached to or built within the footprint of the primary residence and does not include complete facilities (e.g., less than a complete kitchen).

Financing for ADUs

The Housing Trust Silicon Valley has developed an ADU financing program, which provides free informational workshops to interested homeowners, and a loan program to encourage ADU production throughout Santa Clara County. The loan program covers detached ADUs and garage conversions, and requires that a homeowner agree to a 2-year affordability restriction: ADUs built with the loan must be rented to a low-to moderate-income household for at least two years. As financing can otherwise be a major hurdle, having a consistent resource in the region can assist many homeowners in reaching the finish line of their ADU projects. Learn more about the Housing Trust’s Small Homes, Big Impact program.

The California Housing Finance Authority’s (CalHFA) ADU Grant provides up to $40,000 to reimburse pre-development and non-reoccurring closing costs associated with the construction of the ADU for moderate- and low-income homeowners. Predevelopment costs include site prep, architectural designs, permits, soil tests, impact fees, property survey, and energy reports.

ADU Laws

By State law, ADUs are allowed in all cities in California.  Recent changes to State law, established by a series of bills including SB 1069 (Wieckowski, 2016) and AB 2299 (Bloom, 2016) have required local jurisdictions to ease certain zoning regulations to support the creation of ADUs.  Most cities in Santa Clara County updated their ordinances to comply with the new law.

Learn more in our ADU White Paper

In the four years following the passage of these bills, the number of ADUs permitted permits in Santa Clara County have been steadily increasing, as shown in the table below (with a slight decline from 2019 to 2020, during the COVID-19 pandemic).

ADUs Permitted in Santa Clara County: 2017 – 2020
Jurisdiction2017201820192020Total% of Countywide Total
Los Altos82637531245.5%
Los Altos Hills726825662.9%
Los Gatos44328281034.5%
Monte Sereno129149441.9%
Morgan Hill1815315512.3%
Mountain View4151817542.4%
Palo Alto123662431536.8%
San Jose921874163311,02645.3%
Santa Clara4971511356.0%
Unincorporated County172932421205.3%

SV@Home’s Position: We Need New and Innovative Housing Solutions

SV@Home is working to promote policies and implementation actions that increase the number of lots that could qualify for a second unit and that provide flexibility and simplicity for homeowners, including provision of technical assistance and support.

Our policy recommendations for second units focus on:

  • Simplifying and easing development standards: reducing or eliminating minimum lot size requirements to increase the number of properties where second units can be built.
  • Eliminating fees: removing fees decrease overall project costs, allowing more property owners to take advantage of simplified development standards
  • Amnesty: enabling amnesty for units that were illegally built as long as they are brought up to current building codes.
Read more in our ADU White Paper

Additional Resources