How can I legalize an existing unpermitted ADU?

Unpermitted JADUs and ADUs follow the same building permit review process and California Building Code requirements as new construction, very similar to additions or remodels. Attached ADUs will need to have fire rated separations, egress, and separate electrical and mechanical systems per California Building Codes.  The application for building permits should include plans for review and payment of permit fees. Once the permit application is reviewed and issued, then inspections will need to be scheduled and final inspection passed.