In General, there are four ways that an ADU can be created on a property:
- By converting part of the existing home;
- By converting an existing garage or accessory structure;
- By building an addition to the existing home or an existing garage; or
- By building a new, free-standing home on the property.
Each of these options presents advantages and disadvantages, and your personal goals and intentions for the ADU will help you decide how best to build it. Based on the County Code, a Conversion ADU is: "…the conversion of any portion of a legal accessory structure built or issued a building permit prior to January 1, 2017, or any portion of a single-family dwelling, or any garage, for the purpose of creating an accessory dwelling unit."
New Construction ADUs are any ADU that doesn’t meet that definition. See County Code Section 13.10.681 for full details.
The ADU Design Guide can help you visualize the various options, and understand the County’s Zoning standards that apply to ADUs both inside and outside the Urban Services Line.
There are several factors that can influence the cost of constructing an ADU, and the ADU Basics book can guide you through considering whether there are lower cost options that will meet your goals for your ADU. The ADU Basics book will also help you understand the process involved in obtaining your Building Permit and any other permits that might be required for your project.