Homes built on slabs have less risk of flooding or leaking gases, which creates a healthier environment than homes built over crawl spaces and basements that are susceptible to flooding, gas leaks and mold. Slabs often eliminate the need for extra steps because they are lower to the ground. Senior citizens or people with physical restrictions are attracted to one-level homes that don't have a lot of steps to climb.
Shifting soil, invasive tree roots and earthquakes pose serious problems for homes constructed on slabs. Any cracks in the foundation can cause major, long-term issues that are often very difficult and costly to repair. Slabs are prone to insect infestations as well.
Crawl Space Advantages
Crawl spaces can work well in dry climates, and they are generally less expensive to build than basements. Well-insulated crawl spaces built with mold-resistant materials and proper ventilation for your region offer more storage space than a slab but less than a basement.
Crawl Space Disadvantages
Crawl spaces that aren't insulated properly from elements attract moisture, mold and rodents. Vented crawl spaces in homes located in drier climates tend to pose fewer issues than insulated and sealed crawl spaces in humid locations, but none of them yield impressive energy savings compared to homes designed with insulated floors built on slab or over a finished basement. If you must choose a crawl space design for your California home, choose a sealed crawl space that discourages mold and saves energy.