Type of foundation in relation to trees 10 meters away ?

31 Aug 2010
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United Kingdom

We are looking at a 2 story extension to our existing 2 bed end terrace house.

We have had 3 builders round and each have said something different.

The first said the tree distance is borderline, so we would need to have piling to support the foundations (apparently at the cost of an additional £8000).

The 2nd said its over 7 meters away and there Oak trees so its fine.

And finally the 3rd said pretty much the same as the second, but said he would use a 'clay sheeting' or something, can't remember exactly what he called it, just to stop any roots getting to the footings. And maybe to be go an extra 1/2 meter down with the footings.

As you will see from the image the boundary is 9.6 meters away, and the tree closest to the proposed building plot is a further meter beyond.


Does anyone know the standard when it comes to this, I have looked on Google and can't find the answer.


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If you are on clay ground you will be looking in excess of 2m deep. All depends on your soil type really, do not trust someone that says at 7 m oak trees will have no effect on clay ground, they are classed as a high water demand tree.
On the other hand you may have decent ground so no problems.
Unless these three builders are doing a design and build, then they wont have any say in the foundations ... your designer will design them, the council approves them and the builder builds it

But be prepared for some 'non-standard' foundation work and cost
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The girlfriends last house was built on clay near trees - nightmare. House started cracking all over the shop.
Yes the link is ok, I would give your local BC a call and ask for their advise, their local knowledge of ground conditions should be good, your clay may not be classed as highly shrinkable or perhaps you might hit better ground at a certain depth
It would be worth having a soil test. If your clay is medium plasticity (rather than high) it will reduce your foundation depth from 2.5m to 2.15m. The test costs about fifty quid and usually takes a couple of weeks so plan ahead. Only problem is you need to take the soil sample from the clay layer which could be 1.5 or more deep.

PS. that's based on English Oak. If it's a Turkey or Red Oak then high plasticity might tip you over into piling.
I've had a job recently where we have a tree maybe 7-10 meters away from a proposed extension. I think the critical issue is if it's within felling distance from your works. Has it got a Tree Portection Order also?

When applying for Planning Approval, if the works are close to a tree you'll more than likely require some form of Tree Survey / Aboricultural Report. The Local Authority Tree Officer will then step in + give his opinion to the Planning Officer. Only once they're all happy will you be given approval, and more than likely they'll ask for some additonal foundation works.

In our case the Tree Officer TPO'd the tree + has asked us to provide pile foundations along the tree side of the extension, it's been conditioned along with Structural Engineers calcs for the foundations.

They're is no point asking builders for they're opinion at this point. Get it designed + passed, then once you know what you have to build then ask builders for quotations.

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