Accessory Dwelling Units (ADU)

ADU

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What is an Accessory Dwelling Unit (ADU)?

An “ADU” means a building or portion of a building designed for use and occupancy by people living independently of the occupants of the main residence building and containing separate kitchen, bath, sleeping, or living facilities. 

There are three key types of ADUs outlined below:

  • Attached ADU: A newly constructed unit that is connected to the primary main residence by at least one wall.
  • Detached ADU: A newly constructed unit that is freestanding or separate from the primary main residence, like a cottage, pool house, or guesthouse. 
  • Converted ADU: Space within an existing or proposed home (like an attached garage or attic) or within the existing footprint of a permitted accessory structure (like a detached garage or outbuilding), can be converted into an ADU, as long as the space has side and rear setbacks sufficient for safety (per the building and fire codes) and it has its own front door, independent of the main home. Conversions can be a simple as scheduling an inspection and filing paperwork; but they can also require safety upgrades to meet building and fire codes. The Town is currently working on launching an amnesty program for existing buildings that may have already been converted to a dwelling and to help owners identify the extent of work required to convert a structure.   

What is a Junior Accessory Dwelling Unit (JADU)?

A “JADU” means a unit that is no more than five hundred square feet in size and contained entirely within a single-family residence. A junior accessory dwelling unit shall include an efficiency kitchen, which shall include all of the following: a cooking facility with appliances, a food preparation counter and storage cabinets that are of reasonable size in relation to the size of the junior accessory dwelling unit. A junior accessory dwelling unit may include separate sanitation facilities or may share sanitation facilities with the existing structure. 

How to Rent your ADU or Finding an ADU to Rent:

These organizations can help match individuals seeking housing with people who have an ADU to rent and/or can assist homeowners in renting out their ADUs or JADUs. 

  • HIP Housing ADU Match Program: HIP Housing can assist Home Providers as well as Home Seekers. HIP Housing can conduct interviews virtually, in office, or at a home visit. HIP Housing can assist with client applications, conduct background searches, discuss home provider incentives, help determine rent ranges, and provide resource packets for new Providers. General Services include:
    • Provider and Tenant Interviews
    • Tenant Applications 
    • Background Searches
    • Rent Range Categorization
    • Resource Packets
    • Provider/Seeker Matching Program. 
    • Lease Agreements
    • Conflict Resolution Resources

If you are seeking a tenant for your ADU or housemate for a room to rent, this is a sample list of persons seeking housing in Atherton as of March 2025. Please get in touch with HIP Housing at 650-348-6660 x303 for more information.

Other Helpful Resources:

 ***Listing on the above list is not a recommendation by the Town of any particular vendor.

ADU Code Updates 2025

Since Atherton’s last ADU code update in March 2024, California ADU regulations have undergone several changes as part of the state’s effort to address the housing crisis. In response, the Town of Atherton is in the process of updating the ADU ordinance to stay in compliance with new state laws, which includes: SB 477 (2024), SB 1211(2024), AB 1332 (2024), AB 2553 (2024), AB 462 (2025) and SB 543 (2025).

These updates ensure that Atherton’s ADU ordinance remains enforceable by staying consistent with newly adopted state legislation. In the event that Atherton’s ordinance falls out of alignment with the state and does not continue to comply with new laws, the Town’s ordinance risks becoming null and void and superseded by state law.  

In addition to code updates to comply with state law, some updates to the language are also being made to improve clarity in the development review process and address interpretation issues with applicants.

The Planning Commission considered and recommended approval of ADU Code Updates at their regular meeting on September 24, 2025.

The City Council will introduce the amendments for a first meeting at their regular meeting on November 19, 2025. Concurrent with this process, staff will send the draft updates to the State for consideration and approval. The Town anticipates the updates will become effective in early 2026. 

Draft amendments with changes shown in red text.