The cali guys have way different rules to anyone not on a fault line, and for good reason: sooner or later, they will have an earthquake. Digging out a basement under your house haphazardly is a good way to get the house to fall into the basement.

Here in Brisbane getting your house raised is a pretty typical move. Traditional Queenslanders are raised about a metre (3') from the ground, so a lot of people jack 'em up enough to get stuff under there, like parking and laundry and so on. Then you can enclose the space with any old junk, and presto, more living space.

This of course requires your house to be built on pilings (stumps) to begin with, but apparently is pretty cheap, especially since a lot of houses need their stumps replaced anyway. While you're at it, might as well jack the place up.