how deep do pilings need to be

How Deep Do Pilings Need To Be?

As piling contractors, we often get asked the question “How deep do pilings need to be?” In all honesty, there’s not a straightforward answer. The depth of pile foundations will depend on a variety of factors.

Pile foundations are an example of deep foundations and were first used for large constructions. However, since smaller piles have been developed, such as mini piles, we are now able to use this foundation for domestic buildings. 

Pile foundations provide support for structures. They do this by transferring their load to the surrounding layers of soil or rock that have sufficient bearing capacity. The heavier the load above ground, the deeper the foundations need to be. There are other factors that will also affect this, they include:

  • The ground or soil conditions
  • Proximity to other structures
  • type of piles used

Different structures require different types of piling foundations, and you can even read about the piling secrets of the UK’s most famous buildings.

Soil Conditions

Often, the type of soil will determine the type or depth of the piling needed. Some soil types you may encounter include:

  • Rock
  • Gravel
  • Sand
  • Clay
  • Peat
  • Chalk

Less stable soil types, such as sand, peat or clay are likely to require deeper pilings. It can be difficult to know the soil type you’re working with simply by looking at it. Contact your local building control department for information on the types of soil often found in your area.

soil conditions piling

Types of Pile Foundations

Driven Piles

Driven piles are often used to support buildings, towers, walls and bridges. The depth of driven piles depends on the size of the structure and material, but below are some examples of types of driven piles and their maximum lengths:


H Section Piles – Often used in marine structures and can reach up to 36m in length.

Screw Piles – Less soil displacement because of the ‘screwing’ method. Can reach up to 24m in length.

Tube Piles – Used in heavy load support.


Widely used piles due to versatility and suitability to most ground types. They can reach up to 30m in length.


Can be installed on smaller properties with restricted access. Can reach up to 12m in length.

Bored Piles

Bored piles (also known as replacement piles) are a type of piling method where the soil is removed from the ground in order for the hole to be filled with concrete, which is poured in situ. They can reach up to around 40 meters in length and are used for high buildings with heavy vertical loads.

Mini Piles

A mini pile generally has a diameter of between 100 and 600mm but can extend to depths of over 50m. They can be used in most types of soil and are often used for underpinning or strengthening existing structures. Mini piles are generally used for areas where access is restricted or confined spaces.

Geothermal Piles

Geothermal energy is a sustainable source of natural heat energy that is stored in the earth, and geothermal piles not only provide support to a building but also act as a heat source. The depth of geothermal piles depends on the ground conditions.

Do I Need Foundation Piling for my Extension?

Often, a simple house extension won’t need deep piling. Instead, strip foundations, raft foundations or trench-fill foundations will suffice. However, in certain situations where the soil is unstable, you may need piling foundations. A good indication of this is to look at your existing foundations. In most cases, your house will simply require an extension of the current foundations.


Without visiting a site, it’s impossible to advise on the type and depth of piling needed. To discuss your options and arrange a site visit with a qualified piling contractor, please get in touch with us.

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