Foundations near trees ???

[aspley]

I could do with some advice on an issue I have with footing depths near trees.

We are building a bungalow, 10 metres from the back of the bungalow are some Poplar trees but the bases of the trees are down a bank and are a good 2.5 metres below the ground level on which the bungalow is being built.

Ordinarily I would expect to have to go down the best part of 3 metres with footings but of course in this case that will take the footings down to the horizontal level of the tree base.

So question is, as roots do not grow upwards should the presence of the trees be ignored.......it does not answer the question in NHBC guidelines but someone out there may have come across something similar.

 

[mikric]

What are your ground conditions like ? And do you know what type of Poplar they are ?
If you are into clay etc you are beyond the realms of any of the tree tables available as your ground slope is greater than 1 in 7 and as such an engineers design will be required unless your building inspector is brave enough to design your foundations for you.

 

[aspley]

Its medium clay......but my hope is that because the base of the trees are so far below the level of the build they can be ignored. Perversley, any dig down will be taking the footings nearer to the tree roots which I would have thought should be avoided......as you say there aint a lot on the available tables. There is someting in the NHBC guide but that also looks at tree bases above the build level

 

[mikric]

Appreciate your line of thought regarding digging down but there is no getting away from the fact that they are in the zone of ground influence to the new foundations and Poplars are very thirsty high water demand trees that can grow to be massive, your scenario is not detailed in any available tables as you really need specialist site specific guidance and design. The roots potentially will penetrate the ground beneath the foundations and as such will effect ground movement/heave.

 

[jeds]

Agree. The roots will be influential regardless of the slope and Poplar roots are just about the worst case. No point calculating anything - you will be piling.

 

[rssteve]

Sorry to bump an old thread, but I have this exact same issue with an extension. What was the outcome of your foundations, did you pile and if so how deep? Thanks

 

[aspley]

Hi, well, I am still in limbo. Building control are perfectly happy with a 600 dig that gets us to sound low shrink clay.
LABC have never come across this before (hard to believe) and don't have any advice but have asked for engineer designed footings.
The engineers design tells me to go down 2m as per LABC tables......he also has not come across this. Now that seems illogical, I could understand him saying go down 4.8m but not 2m as that just puts the bottom of the footings nearer the horizontal tree roots.
Puzzled?? I am and can't find anywhere else to go.
Any suggestions out there please ??

 

[aspley]

This is the section

 

[Nakajo]

Is that for sale?