A foundation is the lowest part of a building’s structure. Its job is to carry the weight of the building and everything in it (plus wind, snow and seismic loads) and transfer it safely into the soil or rock below without excessive settlement. Foundations are usually built of reinforced concrete, sometimes with concrete block foundation walls, and may sit just below the surface or extend deep into the ground.
For more detail, see our guides Building Foundations 101 and Foundation Types.
Types of foundations
| Category | Type | Typical use |
|---|---|---|
| Shallow | Strip (continuous) footing | Under load-bearing walls |
| Shallow | Pad (spread) footing | Under individual columns |
| Shallow | Slab-on-grade | Houses, warehouses, light buildings on good soil |
| Shallow | Raft (mat) foundation | Whole-building slab where loads are high or soil is weaker |
| Deep | Driven piles | Steel, concrete or timber piles hammered to a bearing layer |
| Deep | Bored or drilled piles, caissons | Holes drilled and filled with reinforced concrete |
| Deep | Helical piles | Screwed-in steel piles for additions, decks and light structures |
Shallow foundations are used where good bearing soil is close to the surface. Deep foundations reach down to stronger soil or rock when the upper layers are weak, compressible or full of fill.
Footing vs foundation
The foundation is the whole system below the superstructure: footings, foundation walls, piers, piles, grade beams and slabs. A footing is the widened base at the bottom of a wall or column that spreads its load over a larger area of soil.
What decides the foundation design
- Soil conditions: bearing capacity, settlement and groundwater, from the geotechnical report.
- Building loads: the weight and layout of the structure above.
- Frost depth: in cold climates, footings go below the local frost line to avoid frost heave.
- Site constraints: neighbouring buildings, property lines and slopes, which may also need shoring.
Site and inspection tips
- Have bearing soil inspected before placing footings where the geotechnical report or code requires it.
- Check footing size, elevation, rebar and dowels before the pour.
- Keep water out of excavations and do not place concrete on frozen or soft ground.
- Install waterproofing or dampproofing and foundation drainage as detailed before backfilling.
- Backfill in lifts and compact as specified to avoid pressure on new walls.
Related terms
Related templates and guides
- Foundations quality checklist
- Design and construction of driven pile foundations
- Handbook of geotechnical investigation design tables
- Design of strapped footing
Frequently asked questions
What is the difference between a footing and a foundation?
The foundation is the whole system that carries the building’s loads into the ground, including walls, piers, piles and slabs. A footing is the widened base at the bottom of a foundation wall or column that spreads the load over enough soil. Every footing is part of a foundation, but not every foundation uses footings.
What are the main types of foundations?
Foundations are grouped into shallow and deep types. Shallow foundations include strip and spread footings, pad footings, slab-on-grade and raft or mat foundations. Deep foundations include driven piles, bored or drilled piles, helical piles and caissons, used where good bearing soil is far below the surface.
Why do footings go below the frost line?
In cold climates, water in the soil freezes and expands, which can lift and crack footings that sit too shallow. Setting footings below the local frost depth, or using frost-protected shallow foundations, prevents frost heave. The required depth is set by the local building code.
Who decides the type of foundation?
The structural engineer, based on the building loads and the geotechnical report. The geotechnical engineer investigates the soil and recommends bearing capacities and suitable foundation types. For simple houses, building code prescriptive tables are sometimes used instead.
Ask AI about this page: ChatGPT, Claude or PerplexityCopy as Markdown