Foundations and Footings: What Goes in the Ground Before Anything Goes Up
Free with emailWhat type of foundations your extension needs, how deep they go, what they cost, and what to expect on dig day.
Foundations are where the money disappears into the ground. Literally. You'll spend thousands of pounds on a hole full of concrete that nobody will ever see again, and if it's wrong, you'll spend thousands more putting it right. The rest of your extension sits on this. Every wall, every roof timber, every kitchen unit. Get the foundations wrong and nothing above them is stable.
The good news: for a typical single-storey rear extension, foundations are straightforward. Your structural engineer designs them, your groundworker digs and pours them, and building control inspects them. Your job is to understand what's happening, know what to check, and have enough contingency in the budget for the surprises that are genuinely common at this stage.
Before foundation work begins, several things must be in place. Your builder should be appointed with a signed contract. Your structural engineer's foundation design must be completed and approved. Building control must be notified (formal notice of commencement, at least two working days before the dig). An LSBUD search must be done to map underground services. Your site should be set up with access for a digger and somewhere to pile spoil. If your extension is near a boundary, your party wall agreement must be completed first.
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