The soil work and the plans come first, and we build to what they call for, not to what's quickest. Once the report and the engineer's plans are in, I sit down with you, and if you're still weighing a slab against a crawl space, I lay out what each one means for repairs and moisture down the road. Then our crew lays out the footprint, digs the footings to the depth on the plans, packs the subgrade, which is the ground the concrete sits on, and sets the forms and rebar, the steel inside that holds the concrete together if it cracks. We pour when the weather lets the concrete set properly, not in the heat of a summer afternoon, and then let it cure, the wait while it gains strength, before anything gets built on top. If the budget has to come down somewhere, I'll tell you plainly to cut it anywhere but the digging and prep, because nobody gets back under a finished house to redo that.
Some of this work runs right into other jobs we do. The concrete footings under an addition, a garage or a porch are the same careful dig and pour on a smaller scale, and builders often have us do both. On commercial and multi-unit property, the foundation is usually one piece of a bigger site, and we also do concrete parking lot building, so one crew answers for the concrete from start to finish.
Slab on grade
A slab suits a lot of new houses because it's one pour with no space underneath to keep dry. The catch is that it moves with the soil, so if the ground shifts, the slab can crack, settle, heave or tilt, which is why the soil report weighs heaviest on this choice.
Crawl space
A crawl space suits owners who want the plumbing, wiring, ducts, insulation and framing within reach later, which makes repairs and remodels much easier than cutting into a slab. The thing to plan for is moisture, because a crawl space that stays damp can damage wood, insulation, ducts and floor framing.
Post-tensioned slab
This is a slab with steel cables run through it and pulled tight after the pour, and it's usually the engineer's call rather than yours. One engineering guide says these slabs allow thinner sections on soils that shrink and swell, so if your soil report flags that, expect it to come up.