From organising services through to soil surveys, groundworks are a critical stage of any self build, and one that can reveal hidden costs. Here’s what you need to know to get off on the right foot

There’s one thing you can guarantee when building your own home: you won’t know what it’s actually going to cost to build until you are out of the ground. A perfectly innocuous-looking plot can hide all sorts of surprises underneath. So, before you buy a site, it’s vital to do some research to ensure you’re not confronted with mains sewer pipes, buried high-voltage cables or soil contamination – all of which can add significant cost and complexity to your build or even preclude development in some extreme cases. Here’s how to approach the groundworks and foundations stage of your project.

Do I need a soil survey?

The groundworks and foundations phase of a self build presents one of most common situations where costly issues can crop up. The cautious approach to managing this is to call in a structural engineer and have them conduct a full-blown soil survey, including digging test trenches. The problem is, they’ll naturally gravitate towards more highly engineered (and expensive) solutions, as they need to protect their reputation (and their professional indemnity insurance).

That’s not to say you shouldn’t investigate your site – there may just be better ways of doing it. Most local building control inspectors are well-versed in soil conditions in their areas, not to mention the impact of issues such as nearby trees. They may ask for a small trial pit to be dug close to where you’re planning to excavate the actual foundations; and should this be all clear, you can be fairly confident that standard strip or trench fill will work for your site, possibly saving you considerable cash at the outset. The inspector will probably insist you commission a professional survey if they identify red flags, such as known shrinkable clays or poor bearing capacities, but doing so would therefore be an essential service rather than a luxury.