How to get foundations for extensions right — and whether you need a trial hole

digging foundations
(Image credit: Getty)

One of the most important decisions when building an extension on any kind of house is the type and depth of your property’s foundations. As well as determining the building’s structural stability, the way the foundations are constructed will have a major impact on your budget. Clearly, the more you need to spend on getting the extension out of the ground, the less money there will be left in your budget for stylistically desirable features like elegant kitchens and super-sized bifold doors.

But it can be confusing, not to mention a little daunting, to know which foundation system is best in what situation, which is where our handy guide comes in. We explain everything, from the types of foundations on offer to how deep they should be.

Ian Rock
Ian Rock

Ian Rock is a chartered surveyor and author of eight popular Haynes Home Manuals including The Haynes Home Extension manual.

Ian Rock

Chartered surveyor Ian Rock MRICS is a director is and the author of eight popular Haynes House Manuals, including the Home Extension Manual, the Self Build Manual and Period Property Manual.

Ian is also the founder of Zennor Consultants. In addition to providing house surveys, Zennor Consultants provide professional guidance on property refurbishment and maintenance as well as advising on the design and construction of home extensions and loft conversions, including planning and Building Regulations compliance.

Ian has recently added a 100m2 extension to his home; he designed and project managed the build and completed much of the interior fit-out on a DIY basis.