Accessory Dwelling Units

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California is in a housing crises; production is not keeping pace with demand, and lack of affordability is a barrier for many people seeking housing.  In response to this crisis, the State of California passed legislation (SB 1069, AB 2299 and AB 2406) that took effect January 1, 2017 to give cities more flexibility and latitude for allowing homeowners to build accessory dwelling units. The goal is to increase affordable housing availability by allowing homeowners to build and rent out an additional unit on any residentially-zoned lot.

Additional state laws (SB 229 and AB 494) effective January 1, 2018 provide further provisions while allowing local agencies to adopt local ordinances that impose additional standards provided they do not prohibit the construction of ADUs.

On January 9, 2018 the Vacaville City Council approved the Accessory Dwelling Unit Ordinance, which will be effective February 9, 2018.  The information on this page reflects the requirements of the new ordinance.


What is an ADU?

An Accessory Dwelling Unit, or ADU, is a secondary dwelling unit on the same site as an owner-occupied primary single-family dwelling. It must have capacity to function as a full-time residence and be equipped with a kitchen, a bathroom, and it's own entrance.

An ADU may be attached to the primary dwelling, or it may be detached. It can be in an existing converted structure such as a garage or shed, or it can be in a new structure. It can be above a garage or in a basement. It may be a manufactured home, but it may not be a camper. Each of these examples has it's own set of standards that it must comply with in order to obtain a building permit.


How do I get one?

You must obtain a building permit to build an ADU or to convert an existing structure into an ADU. Your permit application will be subject to review by the planning department to ensure it is compliant with the regulations set forth by the ordinance. If your application is denied for incompleteness, you may re-apply at any time. If it is denied for non-compliance, planning staff will explain what needs to be done to reach compliance. Permitting and development impact fees will. 

To speak to a planner about ADU requirements, call 707-449-5140.


What are the standards for approval?

The following chart outlines some but not all of the standards set forth by the ordinance. For full details please see Chapter 14.09.122 of the development code.

   Maximum Size  Lot Coverage  Setbacks  Architecture  Deed Restrictions
Detached, Converted 1200 square feet or 50% of primary dwelling size, whichever is less.  N/A  N/A  N/A

1. The property owner must reside on the property, either in the primary or secondary unit.


2. The ADU shall not be sold independently.


3. The ADU shall not be used for short-term rentals.


Detached, New

10% more than current maximum.

Rear yard: up to  35% coverage, as permitted in zoning district.

Under 12ft in height: treated as accessory structure

Roofing, siding, trim, colors and material shall match primary dwelling.

Entrance shall not be visible from the street.

Stairway shall not be in front or side yard.

Over 12ft in height: treated as a residence
All: minimum 8ft from primary residence
Attached, Converted 800 Square feet or 50% of primary dwelling size, whichever is less.  N/A  N/A  N/A (expansion of the primary dwelling is considered "new")
Attached, New

 10% more than current maximum.

Rear yard: up to 35% coverage, as permitted in zoning district. 

 Same as "Detached, New" but may be up to 5 feet from rear and side lot lines.

Roofing, siding, trim, colors and materials shall match primary dwelling.

Entrance shall not be visible from the street.

Stairway shall not be in front or side yards.

 Note: No illegally constructed structure may be converted to an ADU. If renovations include removal of the walls or roof of an existing structure, it will be considered new.