Groundwork & Foundations

Depth of foundations for an extension near trees

Anonymous user 23/02/2024 - 2.45 PM

Hi, we are planning to build a small 3 by 2 metre single storey extension to our existing kitchen. We have had plans drawn up that specify that the foundation need to be 1.8 metres deep as it's clay soil and our neighbours have conifer hedging that is 7 metres from the proposed foundations at the nearest point. So far the building quotes have been incredibly high (due to the depth of foundations) with the builders thinking that this is may be over-engineered with 1.2 metres being fine. The existing house sits on 600mm foundation with an existing extension sitting on 1 metre foundations. We have limited site access so mini diggers are out of the question and builders are quoting for "piling" as they cannot dig this depth by hand. The cost of this work is making it uneconomical as it pushes the cost way over my budget. Is there any scope for me challenging the foundation depth and what is the best way of doing it. Should I dig a 1.2 metre inspection trench to see if there are tree roots and to confirm the soil conidtion? Should I control building control at my Council for advice? All advice gratefully received.