You are wanting to build that new rear or side extension, to give you extra space that is currently lacking within your home.

But there are trees in close proximity and my house is founded on London Clay. What does this mean?

Well depending on the tree type and its distance from the proposed extension will govern the depth of the proposed foundations.

Under normal circumstances (in the absence of trees) foundations would be founded typically 1 metre below ground level. Where trees are present this depth can go beyond 2.5 metres!

This is where your structural engineer comes into play. They will advise you whether its more economical to stay with the traditional trench fill foundation (concrete poured into a trench) or to adopt another approach.

Considerations will be time to dig that deep, health and safety in ensuring the trench does not collapse and the cost of disposing a vast volume of soil not to mention the cost of the concrete.

One option is to use a mini piled solution, which are in effect small columns of concrete that are formed in the ground. There are rig access constraints and cost implications.

A new innovative system is now on the market called Heli Pile, which is a helical aluminium alloy pile of 80mm or 100mm diameter that is easily installed in the ground.

We have just used Heli Piles on one of our extension projects in London, as it was deemed more economical and quicker than a traditional trench fill foundation. The Heli Piles were installed in two days only!

If you have an extension project in mind and your plot is surrounded by trees or even one closely located tree, then please do contact Sketch Structural Engineering for advice.