Accessory Dwelling Units (ADUs)


What is an ADU?

Commonly known as a second unit, granny flat, or in-law unit, an accessory dwelling unit (ADU) is defined as "an attached or a detached residential dwelling unit which provides complete independent living facilities for one or more persons." By definition, an ADU includes permanent provisions for living, sleeping, eating, cooking, and sanitation.

Why are ADUs a big deal?

In September 2016, Governor Brown signed SB 1069, AB 2299, and AB 2406 into law. These bills address local governments’ regulation of ADUs. The purpose of these Government Code amendments, otherwise referred to as the ADU Statute, is to increase the State's supply of housing. The primary effect of the ADU is to significantly curb local regulation of ADUs. Effective January 1, 2017, the ADU Statute nullified the City's existing Second Unit ordinance, Section 17.3.4 of the Orinda Municipal Code (OMC) because the existing City ordinance was in conflict with the ADU Statute. 

How is Orinda dealing with ADUs?

Rather than continue to rely on the ADU Statute, which contains relatively minimal standards, the City adopted a new ADU ordinance in compliance with State law. The new ordinance (17-03) restores some additional local control over ADU applications and provides clarity regarding the standards that apply to the City’s review of such applications. Ordinance 17-03 repeals the City’s existing Second Unit ordinance and incorporates the changes required by State law. 

New Regulations

The new State laws contain specific requirements for the City’s review of accessory dwelling units. These requirements differ depending on whether a unit is 1) wholly contained within an existing structure; 2) new construction is involved; or 3) the lot contains an existing single-family residence. To facilitate review, Section 17.3.4 of the OMC classifies ADUs into three categories. These categories are as follows:

  1. Category 1: ADUs do not create new square footage. 
  2. Category 2: ADUs create new square footage on a lot with an existing single-family residence, either within the residence or in an accessory structure. 
  3. Category 3: ADUs are built in conjunction with a new single-family residence.

ADU Categories

Category 1
Developed Lot 
(No New Floor Area)
Category 2
Developed Lot 
(New Floor Area)
Category 3
Undeveloped Lot
(New Floor Area)
Zoning District RVL-E; RVL; RL-40; RL-20; RL-15; RL-12; RL-10; RL-6 RVL-E; RVL; RL-40; RL-20; RL-15; RL-12; RL-10; RL-6; RM RVL-E; RVL; RL-40; RL-20; RL-15; RL-12; RL-10; RL-6
Density 1 ADU/Lot 1 ADU/Lot 1 ADU/Lot
FAR N/A Lots < 20,000 sq.ft.: See 17.6.8 of the OMC
Lots > 20,000 sq.ft.: 20% of net parcel size
Lots < 20,000 sq.ft.: See 17.6.8 of the OMC
Lots > 20,000 sq.ft.: 20% of net parcel size
Exterior Access Independent from existing residence No passageway required Evaluated in Design Review
Setbacks Sufficient for fire safety Per SFR requirements Per SFR requirements
Height N/A Per OMC 17.4.19; 17.4.20; 17.4.21 Per OMC 17.4.19; 17.4.20; 17.4.21
Maximum Size N/A <50% of existing living area, or 1,200 sq.ft., whichever is less and complies with FAR standards 1,200 sq.ft. and compliance with FAR standards
Parking N/A 1 space per ADU bedroom
(2 spaces max)
1 space per ADU bedroom
(2 spaces max)
City Review Ministerial - 120 days Ministerial - 120 days Design-Review

More Information

For additional information or questions regarding ADUs, please contact Senior Planner, Mayank Patel, via email at or by phone at (925) 253 - 4212.