While there are federal and state standards, the final word on whether you need a building permit for your remodel comes from your city (or county or town if your area is unincorporated).
Each city has its own permitting process, permitting prices and (thank goodness one more time for the Internet) website. As there are some 500 cities, towns and counties in California, generalized answers to building permit questions are hard to come by. You have to research the rules in your own area.
Here are links to some SoCal building departments:
See the whole list, which is found on the newly revamped website of the California Contractors State License Board.