Types of Foundations

House foundations are the structural base upon which a home is built. Their main job is to evenly distribute the weight of the building to the ground and provide stability, preventing settling, shifting, or collapsing over time. The types of foundations used depend heavily on soil conditions, climate, building regulations, and building type.

In the UK, Building Regulations Part A set out specific requirements for foundations:

Below are the most common foundation types:

Shallow Foundations:

Strip Foundations

Strip foundations are a common type of shallow foundation used to support linear structures like load-bearing walls or rows of columns. They consist of a continuous strip of concrete. These foundations are suitable for projects with good bearing capacity soil and are often used in low-to-medium rise domestic buildings.

Pros:

• Simple and relatively low cost.
• Suitable for most stable soils like clay or chalk.

Cons:

• Not ideal for poor or variable soils (e.g. peat, soft clay).
• Vulnerable to movement caused by tree roots or soil shrinkage.

Trench Fill Foundations

Trench fill foundations are a type of shallow foundation where a trench is excavated and then filled with concrete, forming the foundation for a building. This method is commonly used for low-rise structures like houses and garages. It’s a quick and relatively easy way to create a foundation, minimising excavation work compared to traditional strip foundations.

Pros:

• Faster and less labour-intensive than traditional strip foundations.
• Less prone to frost damage.

Cons:

• Requires a lot of concrete (higher cost).
• Unsuitable for unstable ground without additional reinforcement.

Raft Foundations

A raft foundation, is a large, solid slab of reinforced concrete that supports the entire footprint of a building. It’s essentially a “floating” slab of concrete that distributes the building’s load across a wide area, reducing pressure on the ground. This type of foundation is often used in areas with weak or unstable soil, or for buildings with basements.

Pros:

• Distributes load evenly—reduces settlement risk.
• Good for sites with low-bearing capacity.
• Can be quicker than deep foundations.

Cons:

• More expensive and complex than strip foundations.
• Not always economical for small or light structures.

Deep Foundations:

Pile Foundations

Pile foundations are deep foundations that use long, slender elements (piles) to transfer the weight of a structure to a more stable, deeper layer of soil or rock. These piles are typically made of steel or reinforced concrete, and they can be either driven or bored into the ground. They are used when shallow foundations are not suitable due to weak soil conditions or heavy loads.

Pros:

• Suitable for very poor or unstable soil.
• Can bypass weak surface layers to reach firmer ground.

Cons:

• Requires specialist equipment.
• Expensive—generally used only when necessary.

Issues with types of foundations

Issues relating to foundations in residential properties are relatively common, especially due to variable soils, and climate. These issues can affect both old and new builds, and cause a range of defects from minor cracks to serious structural problems. For more information, you can refer to our blog on structural movement however, there is a brief summary of causes of movement below:

🧱 1. Subsidence
When the ground beneath a building sinks, causing the foundation to drop unevenly.

🌊 2. Heave
The opposite of subsidence—when soil swells, lifting the foundation upwards.

🕳️ 3. Settlement
Natural sinking of the ground over time due to the weight of the building, especially common in new builds.

🌲 4. Tree Root Damage
Roots cause both subsidence (drawing out moisture from soil) and structural damage if they invade cracks or drains.

💧 5. Poor Drainage / Water Ingress
Excess water weakens soil around foundations, leading to erosion or instability.

🧰 6. Inadequate Foundation Design
Foundations that are too shallow, too narrow, or inappropriate for the soil type.

⚠️ When to Take Action

You should contact a structural engineer or building surveyor for advice if you notice:

• Cracks wider than 5mm.
• Doors/windows that won’t shut.
• Sudden movement or visible tilting.
• Signs of water pooling near your home’s base.

Additionally, it is vital to seek specialist advice prior to making alterations to a property such as an extension.

For further information, BRE (British Research Establishment) have also published guidance on the assessment of movement in residential housing: Guidance on Assessment of Movement

RICS Qualified

At Avery we have RICS qualified Chartered Building Surveyors who are able to carry out an inspection. We cover most of the North West and North Wales, you can see a list of our RICS Surveyors here.

We are a friendly team and would be happy to have a chat with you before the inspection to find out if you have any specific worries about the property before we begin. We will also go through the report and explain our findings with you to ensure you understand them. If you would like to book a building survey, or find out more about our services, you can contact us via our contact form or call our head office on 0330 088 5040.