See the following link for an Information Bulletin IB-400 prepared by the County of San Diego that summarizes their requirements for ADU’s.
The County of San Diego utilizes the same Permit Ready Building Plans that have been adopted by the City of Encinitas. Applications for Building Permits for ADU’s require the payment of plan check and inspection fees regardless of whether a Permit Ready Building Plan has been utilized. School Fees are required if the project exceeds 500 sf. ADU’s are exempt from Development Impact Fees.
Most projects within the Coastal Overlay Zone require the approval of a Coastal Development Permit. There are certain exemptions that may be available.