Accessory Dwelling Units

What are ADUs?

Accessory Dwelling Units (ADU), also known as granny flats, in-law units, laneway houses, secondary dwelling units, are dwellings that exist on a lot as an addition to the main house and, therefore, are legally apart of the same property. While local climate, history, culture, traditions, customs, and family structures may vary, in general, an ADU may be a detached structure at the front or the back of a residential lot, attached structure to the residence, a lower or upper floor integrated into the main residence, and/or a recovered and remodeled crawl space under a residence.

Advantages of building an ADU on your property:

In the past, local planning regulations had generally discouraged ADUs. Regulations have been changed and now ADUs are encouraged. This is a step in the right direction. Offering more and varied options to house people is a positive thing for any community and demographic segment.

The biggest impact of the secondary dwelling units will be on the family life. Multi-generational cohabitation and a bridge to independent living for the young ones will enrich, preserve and safeguard various steps of the family life. An ADU can be an intelligent and positive addition to people's lifestyle. As a complement to the main residence, an ADU can serve many functions:

  • In-law-unit/granny house
  • Senior and/or children caregiver quarters
  • House caretaker quarters
  • Office suite
  • Play room
  • Hobby room
  • Art studio
  • Guest suite
  • Retreat or study space
  • Income producing rental

Overall, building an ADU can enrich family bonds and add significant value to a residential property when sold or leased/rented.

What are the rules?

ADU legislation is a long overdue set of regulations that allows for additional residential space on single and multi family zoned parcels and mandates city approval for such flexible residential spaces while eliminating any discretionary approvals.

For thousands of years people have lived in various family types and structures. With no or minimal flexibility for multi-generational family life, income producing rentals, in-house care giver or business incubator space, many sources of nurturing for children and safety and security for seniors have disappeared. This is a good piece of legislation for the people and the local communities.

California Legislation: AB 2299, Bloom. Land use: housing: 2nd unit

Key Points:

  • As defined by the legislation, an ADU is a residential dwelling unit that is either attached or detached from the primary residence and provides independent living facilities for one or more persons.
  • An ADU may not have a total area of floor space that exceeds 1,200 square feet (sq ft.).
  • Parking requirements for these buildings will not exceed one space per unit or bedroom.
    • Requirements can be fulfilled by providing tandem parking on an existing driveway or through offstreet parking in setbacks areas as specified by the local agency.
    • Local agencies have the authority to reduce and/or eliminate all parking requirements associated with building and ADU.
  • Local agencies don't have the ability to deny the construction of an ADU based on the purpose of limiting residential growth.
  • An ADU is not intended to be sold separately from the primary residence, but may be rented.

Generally, ADU regulations vary from town to town. If a town has not yet updated its own ADU regulations, the state regulations apply. Interested parties should always first check with the local Planning Departments and personally review the locally enforced ADU regulations. After this first step, such interested parties should retain an Architect to consult with and identify the specific approach and strategy of how to design and get approvals to build the desired ADU.

ADUs designed by DIAP

In-Law Addition - Design / Construction (San Carlos, CA)

Basement Creative Re-use / Rental Apartment

500 SQ. FT.

York Street Remodel (San Francisco, CA)

Remodeling and expansion of the lower level townhouse unit into a two unit condo.

Saturn Street Remodel (San Francisco, CA)

Proposed 3-story 2-unit condo plus basement garage.

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