The Vacaville Municipal Code contains Chapter 14.09.122 which describes Land Use permits and Approvals for ADUs.
One accessory dwelling unit is allowed in all residential zoning districts where single- family dwellings are a permitted use and where there is one existing or proposed single-family dwelling on site, subject to the standards of this chapter.
One accessory dwelling unit is allowed in all residential zoning districts where single-family dwellings are a conditional use and where there is one existing or proposed single-family dwelling on site, subject to the standards of this chapter and the conditional use permit process and criteria as identified in Chapter 14.09.110 of this code.
An accessory dwelling unit shall not count toward the maximum allowable density for the site upon which the accessory dwelling unit is located.
Accessory dwelling units may be attached to, detached from, or located entirely within the living area of the existing primary single-family dwelling.
Accessory dwelling units shall not be created on any site that contains any resource listed in the California Register of Historic Places or is on any abutting site and would be visible from the historic site, unless the unit is contained within the space of an existing building and makes no exterior changes to the building or any changes to the historic site.
For full details please see the Guidelines of the development code.
To speak to a planner about ADU requirements, call 707-449-5140.