Slab foundation building in Cupertino CA - a floor built for the ground it sits on

A reinforced concrete slab in the San Jose area usually runs about $9 to $15 per square foot. Ground that needs more digging or a post-tensioned design moves you around in that range. If the budget gets tight, trim somewhere other than the base, because it's the one part you can't redo once the slab's poured.

Usually, if your soil shrinks and swells, and the Post-Tensioning Institute calls it a cost-efficient, high-performance choice for homes on that ground. The institute says it cuts cracking and keeps cracks tight, so less water reaches your floors. I want the soils engineer's report first, because the ground has more say than we do.

Usually within 48 hours, though concrete takes a month to fully cure, the slow hardening that gives it its strength. To be safe, you may want to wait a week before putting heavier loads on it.

You can check by typing your address into the state's EQ Zapp map, which shows whether a property sits in a mapped earthquake hazard zone. That matters because the state says building in one may mean studying and reducing the hazard during local permitting. The state geological survey also lists a 2002 seismic zone report for the Cupertino area.

Small cracks are normal in concrete, but the bigger risk is moisture coming up from below. One maker of under-slab moisture layers says even small holes in that layer can sharply raise the moisture coming through, which can ruin flooring and delay laying it. We guard that layer, because one torn spot can cause trouble under your floors later.

Yes, if your soil shrinks and swells, because the same institute's manual calls good drainage around the foundation's outer edge critical for its whole life. Plan it with the rest of the project, not after. The manual also says the builder should pass the owner a maintenance plan, so ask for one at handover.