What is an Accessory Dwelling Unit?

An Accessory Dwelling Unit (ADU), also called a second unit, a junior accessory dwelling unit (JADU), granny flat, in-law unit, or backyard cottage, is an additional unit of housing added to a parcel of land containing a single-family home. ADUs can be attached to the main home by converting an extra bedroom, garage or basement, or built as an addition, or they can be completely detached if there is enough space on the lot. ADUs have the potential to yield multiple benefits for residents and communities:

  • New, more affordable homes for smaller households within the fabric of existing neighborhoods
  • Flexible living spaces that meet the needs of families that are branching, blending and aging
  • Supplemental income for homeowners seeking financial stability
  • Housing solutions for specific populations, including formerly homeless, seniors, home healthcare workers, developmentally disabled adults, and teachers
  • Reduced traffic congestion resulting from increased housing supply near public transit
  • Local construction jobs and training opportunities


To learn more about Hello Housing’s work with Accessory Dwelling Units, please check out HelloADU.org, our new website which features Hello Housing’s ADU services which were borne out of partnerships with homeowners, public agencies, major corporations, and philanthropy. HelloADU’s programs are designed to support homeowners through every phase of the design and construction process creating housing stability for existing homeowners while adding new rental units that are affordable to a median-income tenant. At HelloADU.org you can subscribe to The Bright Spot to stay up to date on our offerings and other resources related to accessory dwelling units. And, if you are a professional involved in designing, financing or building ADUs, we invite you to join our Registry as well as review Hello Housing’s Equity Centered Roadmap to Designing Public Benefit Incentives Programs.