raft foundations

Pile Foundations vs. Raft Foundations

If you’ve ever built a house using toy blocks, you’ll know that if you don’t get the foundations right, you risk anything you build on top falling down. Foundations are one of the most important parts of a building, and depending on whether you’re constructing a large-scale building or renovating an existing property by adding an extension, the type of foundations you’ll need will differ.

As a general rule, the taller the building the deeper the foundations will need to be. If you’re building is many storeys high it will need very heavy, deep foundations, whereas if it is a lower building that covers more ground surface area you can use a shallower foundation type. Two common foundation types are pile foundations (deep) and raft foundations (shallow).

Here, we’ll discuss the differences between these two foundations types.

If you’re wondering about the different costs of foundations, we have a cost calculator that will give you an estimate.

Pile Foundations

Pile foundations are driven deep into the ground in order to support very heavy structures. They work especially well in areas where the soil or ground is weak and the load of the building needs to be transferred to more supportive soil deeper underground.

Piles are either driven (or screwed) into the ground or cast in place, which means soil is removed in order to install piles. A pile cap can then be used to link groups of piles and create a larger area for the distribution of the building load onto the piles.

screw piles

There are a few different types of piles, including:

End Bearing Piles. The bottom end of the pile rests on a layer of rock or heavy soil in order to transfer the building load to a strong substrate layer.

Friction Piles. These transfer the building load to the surrounding soil using the entire length of the pile.

Mini Piles. In areas where building is restricted or access is limited, mini piling is used. They cause minimal disruption and have lower noise levels.

Screw Piles. Sometimes referred to as helical piles, these piles are screwed into the ground using spiral blades.

Pile foundations are a complicated foundation type and need to be installed by skilled professionals. because of this, they can be more expensive compared to other foundation types.

Raft Foundations

Raft Foundations, or mat foundations, are essentially a ‘mat’ of concrete that sits either on, or just under, the ground. They typically cover the entire footprint of a building and spread the load that’s placed on top of them.

raft foundations

Raft foundations are best suited to one or two storey buildings or spaces where a basement is required, which is why they are often used for domestic properties. They are easy to construct and fairly inexpensive but can be prone to erosion at their edges. They aren’t usually used in instances where heavy reinforcement may be needed in particular areas.


The best way to figure out the type of foundations needed is to have a consultation with a qualified groundworks expert. Depending on the surrounding soil and size of the building, they can advise on whether pile or raft foundations will be more suited to your construction. Get in touch with us today to arrange a free no-obligation quote.

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