I sat down with J and we figured out economically that California will be hard to retire in - so many really bad cost of living troubles unless we get a very inexpensive place up north and fix it up without permits so our property tax doesn't go up horribly.
If the building permit is for maintenence or repair (new roof, new plumbing, new AC, etc) it won't trigger a tax reassessment. If you're adding additional living rooms, converting a garage to a living space, adding a bathroom, etc then your assessment can go up but just for the space you improved. It can get a little hazy if you pull permits to tear our load bearing walls for an open floorplan (but again, if the county decides to reassess it would be just for that portion of the building and not the whole property). Your Questions Answered: If I Remodel My Home, Will My Property Taxes Go Up? - Howard Jarvis Taxpayers Association
But yes, California keeps getting more expensive each year and even the rural north state is seeing prices rise dramatically from bay area "equity refugees" and from commercial marijuana growers/speculators... Building new homes is crazy expensive (a study on why so few homes were being rebuilt in previously affordable Paradise California showed that just the administrative costs like permits & fees added up to $150,000) so that keeps older homes in high demand.