Chapter 2 — Key Takeaways
Why Foundations Exist
- Foundations solve two problems: they distribute load from the building across enough soil area to prevent bearing failure, and they stabilize the structure against soil movement, frost heave, and settlement.
- Uniform settlement (the building sinks evenly) is tolerable. Differential settlement (different parts sink by different amounts) causes structural damage.
- Frost heave occurs when soil water freezes and expands. Footings must be placed below the local frost depth to avoid it.
Foundation Types
| Type | Common Regions | Key Vulnerability |
|---|---|---|
| Slab-on-grade | South, Southwest | Moisture vapor, expansive soil |
| Crawlspace | Mid-Atlantic, South, rural | Moisture, wood rot, pests |
| Basement | North, cold climates | Water infiltration, lateral pressure, cracking |
Reading Foundation Cracks
| Crack Type | Likely Cause | Urgency |
|---|---|---|
| Hairline vertical, no displacement | Normal shrinkage | Monitor |
| Wider vertical (>1/4"), no displacement | Settlement, usually stable | Monitor; seal |
| Stair-step in block, minor displacement | Differential settlement | Professional evaluation |
| Horizontal in block or poured wall | Lateral earth pressure | Structural engineer immediately |
| Rapidly growing any type | Active problem | Professional evaluation |
Crawlspace Key Facts
- Traditional vented crawlspaces are chronically too humid in most climates.
- Encapsulation (20-mil vapor barrier + sealed vents + humidity control) is the modern solution — cost $3,000–$8,000, very high return on investment.
- Inspect annually: probe sill plates and rim joists, check for mold and pest evidence, look for moisture staining.
- An awl or screwdriver is your most important inspection tool — solid wood resists probing; rotted wood does not.
Basement Key Facts
- Water enters basements through hydrostatic pressure, cracks, and porous concrete.
- Exterior waterproofing stops water at the source ($20,000–$50,000+). Interior drainage manages infiltration ($8,000–$20,000).
- Egress windows are required for any bedroom in a basement — minimum 5.7 square foot opening, sill no more than 44 inches above floor.
- Horizontal cracks = structural engineering evaluation. This is not negotiable.
Drainage: The Most Impactful Preventive Action
- Keep gutters clean and downspouts extending at least 6 feet from the foundation.
- Grade slopes away from the building at a minimum of 1 inch per foot for the first 6 feet.
- A single 6-inch rainstorm on a 1,500 sf roof generates ~560 gallons of water.
- Proper drainage prevents foundation saturation, which prevents hydrostatic pressure, which prevents cracking and structural movement.
The Structural Engineer Rule
Call a structural engineer (not a GC, not a waterproofing company) for: - Any horizontal crack in a foundation wall - Any crack with significant displacement - Visible inward bowing of a foundation wall - Multiple interior symptoms (sticky doors + drywall cracks + sloped floors) suggesting systematic movement - Any rapid crack growth (more than 1/4 inch in one year)
Cost of consultation: $350–$800. Cost of the wrong repair: $10,000–$40,000+
Soil Types Matter
- Gravel/coarse sand = good bearing, good drainage, best scenario
- Clay (especially expansive) = swells when wet, shrinks when dry, variable pressure on foundations
- Fill material = wildcard; quality varies enormously
- USDA Web Soil Survey (websoilsurvey.sc.egov.usda.gov) will tell you your soil type
Next: Chapter 3 — Framing: Wood, Steel, and How Walls and Floors Carry Load