Foundations for house extensions

Foundations, despite being hidden when the project is complete, are essential elements of a building project. If you’re considering building an extension on your property, foundations are one of the first things to plan for. Here, we go through a few factors to consider when planning your extension foundations:

Type of soil

The type of foundation you’ll need will depend on the type of soil on your site. If you’re building upon your garden, it’s worth checking the type of soil. If the wrong foundation is chosen which is not suited to the type of soil on the site, it could see your extension subsiding from potential cracks that could appear over time.

Soil surveys are great for investigating the area to decipher the soil type and therefore the most appropriate foundation for your site.


Depending on the amount of space you have at the back or side of your property (or wherever your extension might be), there will probably be some digging required, so there will need to be some space for some heavy machinery to get through. Otherwise, it’s down to good old fashioned hand tools. If you’re building on your garden it will require digging through soil and grass, whereas side extensions might require digging through concrete.

Type of foundation

No building project is the same, and it’s no different when it comes to foundations. The type of foundation you will require for your extension will depend on a number of factors including your budget and the size. The most common for extensions are;

  • Trenchfill Foundations: Digging a trench to a depth where the soil is at load-bearing capacity and filling it with cement.
  • Strip Foundations: Continuous strips of concrete in a trench which supports load-bearing walls.
  • Piled Foundations: Used if the ground conditions don’t support the above foundations. Piled foundations are columns driven into place to reach stronger layers.

Need a professional company to help lay the foundations of your home extension? You can trust BelowGround to provide you with a first-class service. We’re specialists in providing piling, foundation and underpinning work to the highest of standards to both homeowners and commercial contractors. Contact us today to discuss your project.