The part of your project nobody will ever see is the part everything else depends on. Here is what happens between excavation and the first framing member.
Foundation work is the least glamorous stage of any addition, ADU, or new build, and the only one that cannot be corrected later. Framing errors get shimmed. Finish errors get redone. A foundation poured out of tolerance stays out of tolerance for the life of the building, and every trade that follows inherits the problem. Here is what a properly executed foundation involves.
It starts with the drawings, not the dirt. Structural plans specify footing width and depth, rebar size and spacing, embed and holdown locations, and concrete strength. Those numbers come from a soils report and an engineer's calculations for your specific site and building. They are not suggestions or starting points. The first thing we do on any foundation job is read the drawings carefully and flag anything ambiguous before mobilizing — because the wrong time to discover a conflict is with a concrete truck idling in the street.
Excavation to actual depth. Footing trenches go to the specified depth measured from finished grade, into undisturbed soil. 'Close enough' on footing depth means the footing is bearing partly on fill, and fill settles. In the San Jacinto Valley and other expansive-soil areas, depth requirements are often greater than people expect for exactly this reason.
Forms set to line and grade. Forms are set square, plumb, and to the correct elevation, then braced to hold that position against the pressure of wet concrete. Concrete is heavy and forms that are inadequately braced move during the pour — which produces a foundation that is out of square before anything is built on it.
Reinforcement placed and supported. Rebar goes in at the size, spacing, and lap length the drawings call for, tied at intersections and held off the subgrade on chairs so it sits within the concrete rather than against the dirt. Steel touching soil is steel that will eventually corrode, and corroding rebar expands and splits the concrete around it.
Vapor barrier and embeds. Under conditioned slabs, a vapor barrier over a sand layer stops ground moisture from migrating up through the slab into flooring and framing. Anchor bolts, holdowns, and any plumbing or conduit penetrations are placed to plan before the pour — cutting or drilling them in afterward compromises exactly the reinforcement you just installed.
Inspection before concrete. In every jurisdiction we work in, a foundation inspection happens after steel and embeds are placed and before the pour. We schedule around that window and leave the work genuinely ready — clean, complete, and matching the drawings — so it passes the first time rather than costing a week.
Pour, consolidate, finish, cure. Concrete is placed and consolidated so it fully surrounds the reinforcement without voids, finished to the specified tolerance, and then cured. Curing is not just waiting: concrete gains strength through hydration, and concrete allowed to dry out too quickly in Inland Empire heat never reaches its design strength no matter what was on the ticket.
None of this is exotic. It is a sequence of steps, each of which has a right way and several faster ways. The difference shows up ten years later in a building that is still square.