Foundations for new extension

[Trytosmilefor2025]

So I just had a structural engineer over for calculations for a proposed kitchen extension and he is recommending foundations of 2.4 m in places because of nearby trees from neighbours side. Is it even possible to dig that deep for a single story extension! I have a feeling this will make the costs prohibitive. I just want to check if any one was recommended such deep foundations or if there is anyway around it?

What type are the trees? and how far away will your extension be from the trees when it is completed. Building control / planning usually stipulates how far away you need to build from tree's

It's a cypress tree. It will be about 4 m away from the proposed extension.

It will be safer to use mini piles.

Less digging, less concrete probably similar costs.

Ask your Structural Engineer about using that option.

Good news:

You can use helical screw piles, not used myself (yet), these screw deeply into the ground to support the structure, the piles are linked with a frame to give great stability, you thus need less concrete / materials, as well as being quicker to install (less man hours) with less machinery so this can be a lot cheaper than traditional foundations, as well as giving a better depth of foundations.
an example: https://groundsun.co.uk/closer-look-at-helical-piles/

Put it on a reinforced raft - no digging

Nearby neighbours had deep foundations for their (not very large) kitchen extension because of trees (a mini forest) in next door's garden. A few years later there were structural cracks in the front of the house and it had to be underpinned.

So if there's a chance of subsidence or tree root damage, deep foundations are wise. But try exploring the alternatives PPs have mentioned.

Thank you! Deeper foundations are obviously needed, I will also explore the alternatives above, but any idea of costs at all?