[toast0]

Insulation in California homes depends a lot on where they were built and when. My parents' home in southern california was built in the 1960s, and was pretty much uninsulated, but none of these homes had a/c and the gas heater would be run a few days in the winter. You've got to have a heater to be an inhabitable home by California law, but if it only runs a few days a year, insulation almost doesn't matter. If there's little climate control, not being air sealed is generally a benefit rather than a negative, as it provides passive ventilation, and much of the old housing stock is in areas where the climate is generally pleasant enough all year that outside air is nice enough.

If you've got an attic, it's not too expensive to from zero insulation to basic insulation, and the ROI is pretty quick. Of course, some areas of California had neighborhoods built in the Eichler-style with no attic space; those are hard to add insulation to. A nice large tree over the home can help with summer heat, but large trees over the home have risks and costs too.