Another subsidence question thread!

[Gary Prentice]

If you want any further reading Mark, tree roots in the built environment is a good read.

Edited July 29, 2013 by Gary Prentice

[sloth]

Seems I'd lost track of this thread. All replies appreciated thank you, I'm going to have a little looksy on Wed, and shall let you know how it goes...

[daltontrees]

I am curious to know more about the facts, distance, species etc.

 

I just looked at your original post and I see there was one question that no-one has had a crack at. That is the question of NHBC-standard foundations. I can't answer it but I can ask a supplementary rhetorical-style question that has always nagged at the back of my mind and could be relevant. I would be interested to hear any thoughts on it.

 

The gist of NHBC (this is my own understanding) is that people who buy from volume builders have not commissioned their own architect to design the building and have not had someone representing them inspecting the construction standards during building and therefore have limited and complex comeback if the building starts to fall down. Volume builders created the NHBC as a guarantee scheme against poor design and workmanship. NHBC developed a set of rules for calculating appropriate foundation depths for building on shrinkable clays, presumably so that tey and their members don't receive subsidence claims. The rules seem to have been based on decent research and engineering logic. They seem to have achieved a broad acceptance.

 

So if someone else commissions an architect to design a building for them, that architect must specify the right foundations for the situation (soils, trees, climate etc.). I suspect an architect would be foolish to try and deviate from the NHBC 'rules' (which are only rules for NHBC members but nevertheless have a wider applicability).

 

So to the question. Is someone who has a tree on their property entitled to expect that any right minded builder/designer/client would put up a building on shrinkable clay that was adequate for both (i) existing trees and (ii) trees that could be planted or allowed to grow on adjacent land that is outwith their control? In other words, in assessing the reasonable foreseeability of damage from their tree's roots, is a tree owner right to assume that the foundations of a newish adjacent house will have been designed and built to withstand nearby trees and the dessication they might cause? Would this be a defence a la Berent?

[Gary Prentice]

 

Is someone who has a tree on their property entitled to expect that any right minded builder/designer/client would put up a building on shrinkable clay that was adequate for both (i) existing trees and (ii) trees that could be planted or allowed to grow on adjacent land that is outwith their control?

 

Existing trees yes, I would agree that the NHBC guidelines are almost certainly universally adopted as an industry standard. I seem to recollect a subsidence case where the property wasn't built to this standard and I think the architect got sued.

I'm not sure how the NHBC deal with the likelihood of future plantings. I don't think that allowances are made. 'Tree-related subsidence: Pruning is not the answer' by Oisin Kelly & Dealga P O'Callaghan makes mention of this scenario, but again I don't know if this has been updated or rectified. The NHBC guidelines are pretty heavy going.

 

 

 

In other words, in assessing the reasonable foreseeability of damage from their tree's roots, is a tree owner right to assume that the foundations of a newish adjacent house will have been designed and built to withstand nearby trees and the dessication they might cause? Would this be a defence a la Berent?

 

I would imagine so. I think a judge would have to consider sub-standard construction as a contributory factor in a subsidence claim. It would be foreseeable that an existing tree on a shrinkable soil would have the ability to reduce the load bearing capacity of that soil. Not to design and build a foundation that could compensate for differential movement would incur some liability to the architect.

[daltontrees]

Thanks, most helpful and informative I will endeavour to get a hold of that O'Callaghan piece, it sounds useful and I think was referred to in a recent case. I haven't the strength to go through Berent and Siddiqui and other cases to see which one.

 

So you have alluded to the answer to my question being yes. So in the context of the original post here, shouldn't the neighbour (who as I understand it has built a house recently on adjacent land) have suitable foundations and could the tree owners reasonably foresee this and therefore not have to worry about the risk posed by the tree? HYpothetical question of course.

[sloth]

. So in the context of the original post here, shouldn't the neighbour (who as I understand it has built a house recently on adjacent land) have suitable foundations and could the tree owners reasonably foresee this and therefore not have to worry about the risk posed by the tree? HYpothetical question of course.

 

This is what I was thinking, but am reluctant to tell them so with any degree of certainty!

[daltontrees]

Definitely worth establishing when the newer house was built, though? I'll try and find out when the NHBC guidance came into effect. 2008 is the last version I saw but I don't know itf there was an earlier one.

[Gary Prentice]

Thanks, most helpful and informative I will endeavour to get a hold of that O'Callaghan piece, it sounds useful and I think was referred to in a recent case. I haven't the strength to go through Berent and Siddiqui and other cases to see which one.

 

So you have alluded to the answer to my question being yes. So in the context of the original post here, shouldn't the neighbour (who as I understand it has built a house recently on adjacent land) have suitable foundations and could the tree owners reasonably foresee this and therefore not have to worry about the risk posed by the tree? HYpothetical question of course.

 

http://dealgas-treeconsultancy.co.uk/dealga/files/resources/Tree%20Related%20Subsidence%20Pruning%20is%20not%20the%20answer.pdf

 

Oisin Kelly was the Expert witness for the claimant in Berent and the paper was quoted and agreed by both arbs.

 

Hypothetically yes. this is the gist of Berent, (I think) subsididence is foreseeable as the governing criteria are being met, trees, distance, clays etc, but it may not be necessary to manage/do anything until/unless damage occurs.

 

Wilcox, one of the judges in Berent, said something along the lines that it would result in desertification if every tree that could foresee ably cause damage was removed.

[fagus]

Unreasonable to request tree removal on the premise that could cause subsidence.

Legally the complainant has to provide the evidence.Therefore

even if subsidence is alleged entirely reasonable to ask for soil analysis to prove shrinkable clay on site, evidence of building movement and roots actually present.

Amazing how many people think they have xray eyes in these situations.

 

Foundations must suit the situation if through Council Building Regs the councila re liable if not suitable ,hence seemingly over engineered foundation depths requested. Don't know about NHBC suspect less robust.

[Gary Prentice]

Unreasonable to request tree removal on the premise that could cause subsidence.

Legally the complainant has to provide the evidence.Therefore

even if subsidence is alleged entirely reasonable to ask for soil analysis to prove shrinkable clay on site, evidence of building movement and roots actually present.

Amazing how many people think they have xray eyes in these situations.

 

Foundations must suit the situation if through Council Building Regs the councila re liable if not suitable ,hence seemingly over engineered foundation depths requested. Don't know about NHBC suspect less robust.

 

I wonder under what data the council calculate the foundation depths? I'd suspect that they actually use the NHBC guidelines.