Foundation Types guides

Four foundation types, four failure modes

What fails in a house depends on how it was built. A 1950s slab-on-grade in Texas and a 1920s pier-and-beam in Louisiana have different weak points, different repair economics and different warning signs. Before comparing quotes, know which type you own.

Type	How it is built	Common failure	Typical repair
Slab-on-grade	Concrete slab poured on prepared soil, often post-tensioned	Perimeter settlement, interior voids, plumbing leaks under slab	Piers at the perimeter, slab lifting inside
Crawl space	Perimeter stem wall with piers or block, floor joists above	Footing settlement, joist rot, moisture	Piers, joist repair, drainage and encapsulation
Basement	Concrete or block walls on footings, slab floor	Bowing walls from soil pressure, wall cracks, water	Carbon fibre, anchors, waterproofing
Pier-and-beam	Concrete or wood piers supporting beams and joists	Rotten piers, shimming failure, settlement	Pier replacement, re-shimming, re-levelling

Slab-on-grade

The slab is the floor and the foundation at once. When the soil under a perimeter beam compresses, the edge of the slab drops and the brick veneer cracks in a stair-step pattern. When the soil under the middle erodes, the slab becomes unsupported and feels hollow or bouncy.

Repair splits along that line: perimeter settlement gets piers driven under the beam, interior voids get foam or slurry injection. Post-tensioned slabs need a different approach again — cutting into a tensioned slab without an engineer is dangerous, and a contractor who does not ask whether the slab is post-tensioned should be shown the door.

Crawl space

A crawl space is a structural system with a moisture problem built in. The footings carry the perimeter and the interior piers; the joists carry the floor. Settlement shows up as a sloping floor or a sagging joist, and rot shows up as a soft spot near the plumbing.

Repair order matters: fix drainage and vapour first, then structure. Encapsulating a crawl space without addressing a settled pier hides the problem; installing piers without fixing the moisture means the new wood rots too. The crawl space guide walks the sequence.

Basement

Basement walls hold back soil, and soil pressure is what bows them. A horizontal crack at mid-height with a wall that has moved inward is the classic pattern. The fix depends on how far it has moved: carbon fibre for cracks and light bowing, anchors and excavation for more, rebuild for severe movement.

Waterproofing is a separate trade and a separate budget. Interior drainage and a sump address water after it enters; exterior membrane and drainage address it before. Doing the structural repair without the water repair usually means doing the structural repair twice.

Pier-and-beam

Pier-and-beam lifts the house off the ground, which makes it the easiest type to re-level and the easiest to inspect. It also means the piers are the weak point: wood piers rot, concrete piers settle, shims compress and beams sag between supports.

Re-levelling a pier-and-beam house is genuinely possible — jacking, re-shimming and replacing piers — and it is usually cheaper than a slab repair of similar extent. The trap is a contractor who re-shims without addressing why the pier moved.

The problems hub maps symptoms to each type, and the repair methods hub explains what each fix does. If you are still deciding whether to repair or replace, the comparison hub prices both.

Which foundation type is best?

For repair economics, pier-and-beam is the easiest to inspect and re-level. For energy and moisture, a well-drained slab or a sealed crawl space performs better. "Best" depends on climate and soil, not on a single ranking.

How do I know which type I have?

Look for a crawl space access hatch, a basement stair, or the slab edge at an exterior door. A home inspection report usually names it; a $400 engineer visit confirms it.

Can a slab foundation be re-levelled?

Yes, within limits. Foam or slurry injection lifts a settled slab by inches, not feet, and it does not restore bearing capacity. Significant perimeter settlement needs piers.