Laying the Groundwork and Foundations for an Extension

Laying the Groundwork and Foundations for an Extension

Every extension will require solid groundworks and foundations. Once these are in place you can build your extension with confidence, knowing it has a solid structural base on which to build. Here we look into the extension foundations and groundwork that will likely be required.


cement mixerWhen the groundworks are done it may not look as though your extension is going anywhere fast. However the work done now will ensure your extension is stable and solid.

The groundworks comprise the first part of the job. The foundations can only be completed once the groundworks are complete. This involves clearing the area where the extension will be built. Then the area will be marked out so it is clear where the foundations will need to go. This provides a template, if you will, to follow. The groundworks will then involve digging the trenches to receive the foundations.

The complexity of the groundworks will depend on the area where the extension will go. For example if the ground outside your property immediately slopes away from the house, you will need to either dig into the area to flatten it or build it up if required. Generally speaking, digging into the area would be easier, although it depends on whether you are having a one- or two-storey extension added. The plans should specify what will happen in this case.

Digging foundations for an extension

digging foundationsThe work involved with digging will depend on the ground you are working with. For example if you are building your extension out into the garden you will likely have to dig up grass and earth. However if you are building out sideways onto what is currently a driveway, you may have to dig your foundations through concrete.

In the first example you can dig the foundations for extension by hand if you wish to save money. However in the second example you’d need to break up the concrete so machinery will likely be required (unless you’re happy to tackle some back-breaking work).

Access to the site will also determine how the digging will be done. You can of course hire groundwork companies to get the job done for you if you wish. Just be sure to get a minimum of three quotes so you can compare them and get the best deal. Be aware prices will vary depending on access, how the job has to be done and how long it will therefore take.

Laying foundations for an extension

There are different kinds of foundations that can be used. The first is called trench fill foundations. These are created by filling the trench that’s been dug with cement. It is then levelled and left to completely set and dry before the walls can be built.

The second type of foundation is deep strip foundations. Many people who want to know how to lay foundations for an extension choose this type. They are comprised of a layer of cement to fill in the bottom of the trench followed by blocks. These won’t be seen as they will be below ground level.

Speed and cost will no doubt come into play here when it comes to choosing the method you want to opt for. Trench fill is faster but you pay for that with a higher cost. Deep strip foundations are slower but they are cheaper too, so weigh up the pros and cons of each with regard to your budget.

laying foundations

The foundations don’t stop until you reach the level where the damp-proof course is added. As such the material chosen for the visible portion of the walls will begin to be used once ground level is reached. Therefore, when your foundations have been completed you will likely see the external material (brick for example) creating a line that will mark out the external walls. Inside this will be a cheaper material (usually breeze blocks) to save money and get the interior walls built as quickly as possible.

While it is possible to tackle the foundations of your new extension on your own, you must make sure you follow the plans exactly. The measurements must be precise and the foundations themselves must also be of a good enough quality to pass the building inspection. Most people will opt to hire a builder who can handle the whole process on their behalf. You get the appeal of watching as the foundations for your extension take shape with none of the hard work involved on your part!