PRIVATE - Pile Foundations on a small scale extension?

Pile foundations are not as scary as they sound and are often employed on small scale domestic schemes where ground conditions are poor or the extension is in close proximity to vegetation. 

There is a stigma surrounding pile foundations that they are drastically more expensive than a traditional trench or strip foundation however, this is not always the case. Pile foundations can be a cost effective solution, as we found out on an extension in Leigh, pictured below.

When are piled foundations needed?

You’ll need a qualified assessment and soil investigation to let you know exactly what to expect in terms of the best foundation solution for the ground on your site. Generally speaking, the type of land conditions, or external factors, that could give rise to piling include:

  • Unconsolidated filled materials, artificially imported, which are very difficult to properly compress.

  • Naturally formed and highly compressible subsoils, like peat.

  • Low bearing capacity subsoils which could include wet clay or loose and unstable sand.

  • High water tables that are capable of flushing subsoils, which leads to the risk of erosion and/or sink holes.

  • Subsoils with a propensity for volume change, such as highly shrinkable clay.

  • Proximity to large trees and vegetation.

  • Demolition of existing building and foundations causing unstable ground conditions.


Pile foundations have been used on this extension due to a large oak tree that was within 5m of the extension. An arboricultural survey and structural engineers report concluded that pile foundations would be the most cost effective solution, avoiding a hand dug, 2m deep trench foundation.