# Building Foundations 101 – Learning To Build Better

> In this article we cover each of the different building foundation types, the pros and cons of each and which you should use in each soil type.

- URL: https://essential.construction/academy/tutorials/building-foundations/
- Author: Kyle Parry (https://essential.construction/about-us/kyle-parry/, https://www.linkedin.com/in/kyleparry/) - Kyle Parry is the founder of Essential Construction. He has worked in construction for more than 20 years, leading projects across Canada for the country's largest contractors and developers.
- Publisher: Essential Construction (https://essential.construction/)
- Last updated: 2026-11-03

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Building foundations are the part of a structure that transfers its weight and loads safely into the ground. They hold up the building and make sure it doesn’t sink, tilt or move. Foundations are either shallow (footings, pads, strips and rafts) or deep (piles, piers and caissons), and the right choice depends mainly on the loads and the soil.

A building structure is typically broken down into two main categories, above grade - the superstructure and below grade, the substructure. The general misconception is that the structural element which transmits the load to the soil (such as a footing) is the foundation, however, the substructure (or anything below grade) is otherwise known as the foundation and this forms the base for any structure. Foundations are a significant cost item: for a typical new US single-family home, the National Association of Home Builders' 2024 cost survey puts the foundation stage (excavation, concrete, retaining walls and backfill) at about 10.5% of construction cost, and on poor ground or for heavy buildings the share can be much higher.

##### What is the objective of a foundation?

A foundation serves the following purposes:

- To distribute the total load coming from the structure on a larger area.
- To support the superstructures.
- To give enough stability to the structures against various disturbing forces, such as wind and rain.
- To prepare a level surface for above grade construction work.

Not all foundations are created equally, and each has its own use cases. In this section we’re going to run through each of the types, when you should use them and the pros and cons of each.

This article will break down as follows:

### Table Of Contents

- What are the two different types of building foundations?
- Foundation vs footing: what's the difference?
- What are the most common types of shallow building foundations?
- What are the most common types of deep foundations?
- Building foundation types compared
- Residential foundations: slab, crawlspace and basement
- Foundations for high-rise buildings
- How a building foundation is built: step by step
- Building foundations FAQ

Let’s get started:

### What are the two different types of building foundations?

In general building foundations can be classified into one of two main categories:

- Shallow Foundations
- Deep Foundations

A **Shallow Foundation** is defined as being a foundation where its depth is equal to or less than its width. Think the footings on your house, or on a shed.

A **Deep Foundation** on the other hand is a type of foundation where its depth is greater than its width. An example of deep foundations would be piles or caissons.

With the definitions out of the way, let's now dig into the different types of each of these foundations.

### Foundation vs footing: what's the difference?

The two words are often used interchangeably on site, but they are not quite the same thing. The **foundation** is the whole substructure below grade that supports the building, including foundation walls, grade beams, piles and slabs. A **footing** is one element of a shallow foundation: the widened base, usually reinforced concrete, that spreads the load from a wall or column onto the soil.

So every footing is part of a foundation, but not every foundation has footings. A piled building, for example, transfers its loads through piles and pile caps instead.

### What are the most common types of shallow building foundations?

The four most common types of shallow building foundations include:

- Spread footing
- Combined footing
- Strap Footing
- Mat Foundation or Raft Foundation

##### Spread / Pad Footing

Spread footings are those which spread the super-imposed load of wall or column over a larger area. These are typically found on houses and low rise structures. Spread footings can support either columns or walls.

There are various different types of spread footings including:

- **Single footing for column:** In which the loaded area of the column has been spread to the large size through a single spread. The base is generally made of concrete.
- **Stepped footing for column:** This type of footing is provided for heavily loaded columns which require greater spread with steps. The base is generally made of concrete.
- **Sloped footing for column:** In this type of footing, the concrete base does not have uniform thickness but is made sloped.
- **Wall footing without step:** It consists of a concrete base without any steps, including the masonry wall.
- **Stepped footing for wall:** It consists of a masonry wall having a stepped footing with a concrete base.

![Pad footing for a column](https://essential.construction/academy/wp-content/uploads/sites/22/2024/08/image-1-1024x576.png)

##### Grillage Foundation

A grillage foundation is a special type of isolated footing generally provided for heavily loaded steel columns and used in locations where the bearing capacity of the soil is poor.

The load of the steel column is distributed over a very large area by means of two or more tiers of steel beams and joists which can be consolidated using concrete.

Each layer is laid at a right angle to the layer below it. Below is a figure illustrating a grillage foundation:

![Image illustrating a grillage foundation.](https://essential.construction/academy/wp-content/uploads/sites/22/2024/08/image-1009x1024.png)

##### Combined Footing

A spread footing that supports two or more columns is termed as combined footing.

The combined footing may be of the following kinds:

- **Rectangular combined footing:** The combined footings will be provided in rectangular shape if columns carry equal loads. The design of rectangular combined footing should be done in such a way that the center of gravity of the column coincides with the centroid of the footing area.
- **Trapezoidal combined footing:** If columns carry unequal loads, the footing is of trapezoidal shape.
- **Combined column-wall footing:** It may be required to provide a combined footing for a column and a wall where they sit close together.

##### Strap Footing

If an independent footing of two columns is connected by a beam, it is called a strap footing. A strap footing may be used where the distance between the columns is so great that trapezoidal footing becomes quite narrow. The strap does not remain in contact with soil and does not transfer any pressure to the soil.

##### Raft Foundation

A raft foundation is a combined footing that covers the entire area beneath a structure and supports all the walls and columns.

They are used in areas where the soil masses contain compressible lenses, or the soil is sufficiently erratic so that differential settlement would be difficult to control.

Raft foundations may be divided into three types based on their design and construction:

- Solid slab system
- Beam slab system
- Cellular system

All three types are basically the same, consisting of a large, generally unbroken area of slab covering the whole or large part of the structure.

![Raft slab foundation](https://essential.construction/academy/wp-content/uploads/sites/22/2024/08/image-2.png)

### What are the most common types of deep foundations?

Unlike shallow foundations, deep foundations distribute the load of superstructure into the ground vertically rather than laterally. The three most common types of deep building foundations include:

- Pile foundation
- Pier foundation
- Caissons or Well foundation

##### Pile Foundation

Pile foundation is a type of foundation in which the loads are taken to a low level by means of vertical members, which may be timber, concrete, or steel.

Pile foundation may be adopted when no firm bearing strata is available and the loading is uneven. Depending on the ground, piles carry the load through end bearing on a firm layer, through skin friction along their length, or a combination of both.

Piles may be of the following types:

- **Sheet Piles** - sheet piles are used for the retaining walls such as dock walls and other marine works. They help to protect against erosion and help to retain the sides of foundation trenches.
- **End bearing piles**: These types of piles are used to transfer load through water or soft soil to a suitable bearing material.
- **Friction pile**: Friction piles are used to transfer loads to a depth of friction load-carrying material by means of skin friction along the length of piles.
- **Compaction pile**: unlike the piles noted above, compaction piles do not typically support the structure directly, rather are used to compact loose granular soils, thus increasing their bearing capacity.

##### Pier Foundation

A pier foundation consists of one or many cylindrical columns to support and transfer large superimposed load to the firm strata below. These can include caissons, masonry piers, concrete piers, timber piers or steel piers.

Generally these piers consist of a dug hole down to more stable soil or rock, then the hole is filled with concrete, stone and or rebar. A pile cap is then traditionally installed on the top of the piers to help spread the weight across multiple piers.

Generally, pier foundations are shallower in depth than pile foundation.

![pier / caisson foundation](https://essential.construction/academy/wp-content/uploads/sites/22/2024/08/image-3-1024x566.png)

##### Caissons / Well Foundation

Well foundation or caisson are box-like structures which are sunk from the surface of either land or water to the desired depth.

They are much larger than the pier foundation or drilled caissons. Caisson foundations are used for major foundation works like:

- Bridge piers
- Docks
- Large waterfront structures

##### Factors to consider when selecting a foundation type for your building.

While foundation selection can be a complex process, there are a number of factors that you should consider, those include:

**Economic** - how important is the building and what is the expected life cycle of the structure? As an example, is this a commercial space that will be torn down in 50 years or is this a stadium that needs to stand for 100 years?

**Code Related**- what do the building codes in your area say about foundations? Typically buildings are required to meet minimum life expectancy and design requirements that are outlined in your building code.

**Size of the Superstructure** - how big is your building and what will the loads be that are imposed on your foundation from your above grade structure.

**Building Use** - different uses will have lower or higher loads depending on their end user requirements. As an example, an office building might have higher loading requirements than a residential building.

**Water level**- a high water table can impact your foundation selection and make specific types of building foundations non-viable. Understand where the water is relative to your building foundation will help you in your foundation selection.

**Existing Soils** - the type of soil your building will be founded on has a huge impact on the foundation selection.

The subject of soil and how it impacts your foundation selection requires a deeper dive, so let's get into it.

![strip footings](https://essential.construction/academy/wp-content/uploads/sites/22/2024/08/image-4-1024x675.png)

##### Selection of Foundation Based on Different Types of Soil

Depending upon your soil condition, a different foundation type is recommended. Below we've summarized general foundation types based on which soil is present on your site.

**Foundation recommendations for hard soils**(rocks, hard sound chalk, sand and gravel, sand and gravel with little clay content, and dense silty sand) include strip foundation, pad foundations and raft foundations.

The following factors should be taken into account when finalizing your foundation selection:

- The underside of the foundation must sit below the depth that frost can reach. In the UK, NHBC guidance asks for at least 450 mm below finished ground level in frost-susceptible soils; in North America the local frost depth set by your building code governs (the IRC also requires exterior footings at least 12 inches below undisturbed ground).
- Strip or trench base shall be kept above groundwater table if possible.
- Sand slopes possibly eroded by surface water, so protect foundation by perimeter drainage.
- Weathered rock needs to be given proper attention.

**Foundation recommendations for Uniform Firm and Stiff Clay** include reinforced pile in locations of any trees or vegetation that was removed, strip foundations, raft foundations.

The following factors should be taken into account when finalizing your foundation selection:

- Piles shall be tied properly into suspended reinforced concrete slabs or ground beams.
- Sufficient length of slab shall be provided to withstand clay heave force.
- Special pile design may be needed for clay slopes greater than 1 in 10 because creep possibly occurs. In few cases, reinforced trench fill could be employed.
- Take the foundation below the zone of seasonal shrinking and swelling. NHBC guidance sets minimum depths of 0.75 m, 0.9 m and 1.0 m for clays of low, medium and high volume change potential, with deeper foundations needed near trees.
- When strip foundation is constructed in desiccated clay in dry soil, then the foundation shall be loaded with the building prior to the return of rains.
- Specially designed trench fills or ground beams may be required if the foundation location is in close proximity to trees.

**Foundation recommendations for Soft Soil**(soft clay, soft silty clay, soft sandy clay, and soft silty sand) include wide strip footings, raft foundations, pile to rock or firmer soil below, pier and beam foundations.

The following factors should be taken into account when finalizing your foundation selection in soft soil:

- Wide strip footing is used when bearing capacity is sufficient and predicted settlement is acceptable.
- Strip footing shall be reinforced based on the thickness and projection beyond wall face.
- Frequently, Sub-soil can be improved using vibro treatment, and it would be an economical solution if employed in conjunction with strip or raft foundation.

**Foundation recommendations for peat**include concrete piles extending to firmer soil below, pad and beam foundations, raft foundations**.**

The following factors should be taken into account when finalizing your foundation selection in peat:

- Pile types include bored cast in place with temporary casing, driven cast in place, and driven precast concrete.
- Allow for peat consolidation drag on piles.
- Special high grade and protection is likely to be required in aggressive peats.
- If peat layer is shallow over firm layer of soil, dig it out and replace it with compacted fill. For this, use raft or reinforced wide spread foundation dependent on anticipated settlement.
- Frequently, sub-soil can be improved using vibro treatment, and it would be an economical solution if employed in conjunction with strip or raft foundation.

### Building foundation types compared

Use this table as a quick reference. Final selection always comes from the structural engineer, based on the geotechnical report.

| Foundation type | Shallow or deep | Typical use | Best suited to | Watch out for |
| --- | --- | --- | --- | --- |
| Pad (spread) footing | Shallow | Individual columns | Firm ground near the surface | Differential settlement between pads on variable ground |
| Strip footing | Shallow | Load-bearing walls, houses and low-rise buildings | Firm, uniform soil | Shrinkable clay and nearby trees |
| Combined / strap footing | Shallow | Columns close together or near a boundary | Firm soil with site constraints | Design must keep the load centred on the footing |
| Raft (mat) foundation | Shallow | Whole building footprint on one slab | Weak or variable soil, heavy loads spread over a large area | Large concrete volume and pour planning |
| Piles | Deep | Heavy or tall buildings, poor ground, high water table | Soft ground over a firm stratum, or soils that carry load in friction | Specialist rigs, noise and vibration, load testing |
| Piers / drilled shafts | Deep | Concentrated column loads | Firm stratum or rock reachable by drilling | Groundwater and hole stability during drilling |
| Caissons (well foundations) | Deep | Bridges, docks and waterfront structures | Work in or near water | Cost and complexity |

### Residential foundations: slab, crawlspace and basement

Homes use the same footings described above, but builders usually talk about residential foundations by what sits on top of them:

- **Slab-on-grade:** a concrete slab cast on prepared ground, usually with thickened edges or strip footings around the perimeter. Quick and economical on level, firm sites.
- **Crawlspace:** short foundation walls or piers on footings, leaving a shallow void under the floor for services and ventilation. Useful on sloping sites and where services need access.
- **Basement:** full-height foundation walls on footings, creating usable space below grade. Common where frost depth already requires deep footings, but needs good waterproofing and drainage.
- **Pier and beam:** posts or piers on individual footings carrying beams that support the floor. Suits expansive or uneven ground and lightweight structures.

### Foundations for high-rise buildings

Tall buildings put very large, concentrated loads on the ground, plus wind and seismic forces that try to overturn them. That usually rules out simple footings. High-rise building foundations are typically one of the following:

- **Piled foundations** with heavy pile caps, taking load down to a strong stratum or bedrock.
- **Mat (raft) foundations**, often several feet thick, where competent ground is close to the surface.
- **Piled rafts**, where the raft and the piles share the load to control settlement.
- **Drilled shafts or caissons** socketed into rock under the main columns and cores.

Because so much depends on the ground, high-rise foundation design starts with a detailed site investigation, and the piles are usually load tested on site before production piling begins.

### How a building foundation is built: step by step

Every project is different, but foundation construction for a typical concrete foundation follows this sequence:

1. **Site investigation.** A geotechnical engineer drills boreholes or digs test pits and reports on soil type, bearing capacity and groundwater. Our [Handbook of Geotechnical Investigation Design Tables](https://essential.construction/files/information/e-books/handbook-of-geotechnical-investigation-design-tables/) is a useful reference.
2. **Foundation design.** The structural engineer chooses the foundation type and sizes it for the loads and the soil.
3. **Setting out.** The surveyor marks out gridlines, footing positions and levels from the drawings.
4. **Excavation.** Dig to the design depth, keep the excavation dry and safe, and check it against a checklist such as our [QA/QC Checklist – Site Works (Excavation)](https://essential.construction/files/construction/quality/qaqc-checklist-site-works-excavation/).
5. **Formation inspection.** The engineer or building inspector checks the bottom of the excavation before any concrete goes in. Soft spots are dug out and replaced.
6. **Blinding, formwork and reinforcement.** Place a blinding layer, then fix the formwork and rebar, including starter bars for walls and columns.
7. **Pre-pour inspection and pour.** Check cover, rebar, embeds and levels with a [concrete pre-pour checklist](https://essential.construction/files/construction/quality/concrete-pre-pour-checklist-template/), then place and compact the concrete. In winter, follow a plan for [cold weather concrete](https://essential.construction/academy/tutorials/cold-weather-concrete/).
8. **Curing and protection.** Keep the concrete moist and protected from freezing until it gains strength.
9. **Waterproofing, drainage and backfill.** Apply waterproofing or damp-proofing to below-grade walls, install perimeter drainage and backfill in compacted layers.

### Building foundations FAQ

#### What are the two main types of building foundations?

Building foundations are either shallow or deep. Shallow foundations, such as pad, strip and raft foundations, spread the load into soil close to the surface. Deep foundations, such as piles, piers and caissons, carry the load down to stronger ground further below.

#### What is the foundation of a building called?

The part of a building below ground is called the substructure, and the foundation is its load-carrying part. Depending on the type, you will hear it called a footing, strip, pad, raft (mat), pile, pier or caisson.

#### What is the difference between a foundation and a footing?

The foundation is the whole substructure that carries the building into the ground. A footing is one element of a shallow foundation: the widened concrete base under a wall or column that spreads its load onto the soil.

#### Which type of foundation is the strongest?

There is no single strongest foundation. Deep foundations such as piles and caissons can carry the heaviest loads where good ground is deep, while a raft suits weak soil under the whole building. The right foundation is the one designed for your loads and your soil.

#### How deep should building foundations be?

Deep enough to reach soil that can carry the load, below the frost line, and below the zone where clay shrinks and swells. Minimum depths are set by your local building code and site investigation, and the structural engineer confirms the final depth.

### Related templates and guides

Foundations are the structure that we build our homes, our places of work and our lives on. Getting them right is imperative. For further reading and other helpful resources on this subject, check out the below links:

- [Design and Construction of Driven Pile Foundations Whitepaper](https://essential.construction/files/information/white-papers/design-and-construction-of-driven-pile-foundations/)
- [Foundations Quality Checklist Template](https://essential.construction/files/construction/quality/foundations-quality-checklist/)
- [The ultimate guide to formwork](https://essential.construction/academy/tutorials/a-best-guide-to-formwork/)
- [Design of Strapped Footing](https://essential.construction/files/design/design-of-strapped-footing/)