Historically, few California houses have had basements. Virtually all of the tract houses put up during the post­World War II housing boom were built on slabs or stem wall foundations, and so are most of today's new houses. But in the past few years, more and more California homeowners have been showing an interest in basements. Much of this has to do with increasingly restrictive building permit conditions. In the area south of San Francisco, where I work, many planning departments restrict building footprints to a specified percentage of the building lot. Such floor-area ratio restrictions often make it impossible for owners of existing homes to gain the floor space they want with a conventional addition. At the same time, height restrictions designed to preserve existing views may prevent them from raising the roof and adding another story.

Other than moving to a larger home, that leaves adding downward as the only alternative for the homeowner who wants more space. Retrofitting a basement isn't easy or inexpensive, but property values in the Bay area are high enough to make it a practical option for many homeowners. My company, Bill Brown Construction, specializes in high-end...

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