Depth of Foundation - Leyland Cypress

Rav3nscourt

Hello!
Longtime reader, first time poster.
We have just had structural drawings through from an engineer for proposed renovation works we are planning, including knocking a wall internally. The engineer has come back advising that since we have a Leyland cypress hedge 5m away from the proposed box frame, the foundation depth needs to be 2.5m despite there being an existing foundation in situ.

Does anyone have any experience of this? The research I've done suggests the calculation is based on a tree height of 20m rather than the actual height of the hedge (2.2m) and doesn't seem to take into consideration there is an existing foundation. I know I'm not a structural engineer but I'm asking as we had a builder out to look at the drawings and he was surprised by it and said he's not even insured past 2m and has never had to dig foundation that deep in his 30 years of experience building extensions etc 

Any advice would be welcome! We are trying to get building regs to come out for a meeting for their opinion as well.

 Cheers.

stuart45

They go by the NHBC foundation calculator. Trees are taken at their mature height unless being removed. 
Depends on the soil type of shrinkable clay eg High, medium or low.
I have done them as deep as 2.5M when the Leylandii were only 1M away. 

FreeBear

Are you in a position to remove the Leylandii ?

They are a real thug of a tree, and are not the best thing to plant in a garden. If the tree(s) can not be removed, and the builder won't dig done to 2.5m, would he and the SE consider piling ?

Rav3nscourt

It's the neighbours hedge. We're going to talk to them this evening about removing and replacing with a different plant or fence so that may be an option.

 

TELLIT01

Restricting the height of the hedge doesn't restrict root growth, although it may well slow the rate at which it expands.