Do I Need Foundation Piling for My Extension? 

Published: 31st October 2016.

If you’re planning to add an extension to your current home, you’ll have to ascertain what type of foundation will be needed to accommodate your project. But how do you determine whether you require a traditional or deep (i.e. piled) foundation?

We’re going to offer some insight into what goes into determining the type of foundation that is required. But it’s important to keep in mind that there’s no substitute for calling out a qualified professional for a first-hand inspection. This is the only way to determine precisely what type of foundation is needed to accommodate your extension. 

The Main Types of Foundations Used for House Extensions

Here is a quick overview of the main types of foundations that are used for residential projects:

• Strip Foundation: Essentially a continuous strip of concrete, a strip foundation may be suitable for supporting load-bearing walls for a single-storey house. 
• Raft Foundation: Sometimes soil is too weak to bear the load with a traditional foundation. This may occur when building on clay or peat. In this case, a reinforced concrete ‘raft’ distributes the load over a much broader area. 
• Trench-Fill: This is a simplified version of a strip foundation. In this case, the contractors will dig a trench to an appropriate depth and pour concrete directly into it. The concrete will likely be reinforced. 
• Pad Foundation: This type of foundation is used to support isolated loads, such as those created with heavy steel beams, or at joint intersections for post-and-beam frame houses.
• Piled Foundation: When the soil is unstable or incapable of bearing the load on its own, a piled foundation will create a much stronger support structure on which to extend your house. If the soil has much sand, clay or peat, this will be the most effective way of building out the foundation.

Take a look at your current foundation. It’s likely that an extension of your house will simply require a straightforward extension of that foundation. 

A Word on Soil Types

In determining whether a piling foundation will be needed to accommodate your extension, you have to take soil conditions into account. In fact, even if you have already established the need for pilings, the soil will determine which type of pilings are required.

If you’re curious to learn more about the soil in your area, you may try calling your local building control department. They will probably have generalised information on the kind of soil found in your area. They can also give you an idea of the type of foundation needed. The Planning Portal also has useful resources.

To give you an idea, here are some of the various types of soil you may encounter:

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

Less stable soils (such as those composed of sand, clay or peat) will almost certainly require pilings. It’s also worth noting that there are some situations in which excavating for the foundation could end up compromising the soil at the site. If this happens, then it becomes necessary to provide further underpinning for stability’s sake. To accomplish this, you’ll need a qualified team to deepen the foundation and create a more stable foundation structure.

Each property is different. Please don’t hesitate to get in touch with us if you’d like to learn more. We can help you determine whether your extension will require foundation pilings.