A foundation distributes a building's weight to the earth. It must resist settling, shifting, and moisture intrusion.
Types
- Slab-on-grade: Concrete slab poured directly on compacted soil (simplest, cheapest)
- Crawl space: Raised foundation with 18–48" clearance underneath
- Full basement: 8+ ft walls below grade (most expensive, adds livable space)
- Pier/pile: Columns driven deep into load-bearing soil/rock (soft soil, waterfront)
Footing Depth
Must extend below frost line (varies by region: 12" in Texas, 48" in Minnesota). Undersized footings cause cracking and settling.
Why Frost Line Depth Varies So Much by Region
Water expands roughly 9% when it freezes — if a footing sits above the frost line, seasonal freeze-thaw cycles in the soil beneath it can heave the foundation up and down each year, eventually cracking it. This is why footing depth requirements range from just 12 inches in warm climates to 48+ inches in the northern U.S. and Canada, driven entirely by regional climate, not soil type.
Signs of Foundation Problems
Diagonal cracks near door and window corners, doors that stick or won't latch properly, and visibly uneven floors are the most common early warning signs of foundation settlement — catching these early, before they widen significantly, usually means a far less expensive repair than waiting for structural damage to become obvious.