I get many calls every week regarding foundation cracks, interior finish cracks, and sticking doors. The following provides some general information to consider for a concerned homeowner.
I have structurally designed several of the housing tracts here in Bay Area including houses built by Centex, McBail, and Black Diamond to name a few. The soil, as in most of the Bay Area, is predominately highly expansive clay except for some areas (e.g. Oakley) that are sand. The expansive clays swell in the winter due to an increase in moisture and shrink in the summer upon drying. This annual cyclic process of shrinking and swelling is a likely candidate for foundation movement. The cyclic moisture variation could be caused by rainfall, poor drainage, or possibly a leaking water or sewer pipe. There are other possible sources of issues creating this problem including a cut-fill lot grading condition or a poor soil fill during preparation of the lot during construction.
The foundation flexibility combined with cyclic movement in the support soil telegraph the movement to the building causing brittle finish cracking and sticking doors. Often this movement is not a structural issue but a nuisance finish problem that irritates the occupant. Exterior finish or concrete cracks will need to be sealed to protect the material from degradation. Much less likely, large cracks and movements will cause structural concern depending on the amount of movement and type of framing.
The first step as a homeowner would be to look carefully at your lot drainage and make sure that the water drains away from the house. The crawl space (if you have one) should always be dry even in winter. No crawl space or no vented condition would indicate you have a slab on grade or mat foundation. The water should drain from the back yard to the street quickly preferably through a closed conduit system. You also need to look and your landscape irrigation and make sure that follows the same drainage pattern. I would strongly suggest placing a concrete walk or patio around the entire house and remove any planting beds next to the foundation. If planting beds are built, place them in raised planters over the slab. This is the cheapest and easiest way to mitigate a foundation movement problem associated with expansive soils.
Proper foundation repairs can be complex and expensive and more than likely not worth the benefit. Costs for such extensive repairs can be $100K to $200K. Cheaper repairs (although still expensive) can be performed but may not completely address and/or resolve the problem. Cheaper repairs typically only propose what they can do and not necessarily what science would require to resolve the problem. Consider the case of perimeter jacking, the contractor installs jacks around the perimeter of the house to stabilize the perimeter. These jacks may not provide sufficient uplift capacity as well as the interior foundation is not repaired at all due to a lack of construction access. Foundation repair is a difficult and expensive alternative and should be approached cautiously with extensive research using scientific methods. Your success will be highly dependent on your budget and skill of your design professionals (Geotechnical and Structural Engineer). Seems like the best defense is a good offense which would be to consider not purchasing a home from a builder with a poor reputation or home showing signs of finish distress that aggravate you.
Sadly, I must report, I get calls regarding this issue all over the Bay Area every week. My initial recommendations are to address the drainage issues as discussed above. If the problem persists, then an engineering investigation may be required.
thank you very much