Are oak tree roots likely to circumvent a 3.3m deep root barrier?

[The Professor]

I am in the final stages of purchasing a 1930's semi-detached house in south-east London. During the purchasing process, I have found out that the house had its rear wall underpinned in 2008 to stop subsidence which was identified as being caused by an circa 80-year old oak tree which is sucking all the moisture from the clay soil. The oak is located on an unadopted side road 16 metres from the house's back wall. The insurance company drilled 3 bore holes around the property and did DNA tests that revealed 80% of roots present were oak (it's the only oak in the area). An ornamental acer and cherry (the other 20% of roots found) were removed from the garden.

Unfortunately, in 2014, the property began to subside again, so the insurance company underpinned the house's rear wall once more with 3.3m of concrete, which they call a 'root barrier'. They tried to carry out works to the oak tree in 2014, but neighbours formed a campaign group which has resulted in the oak being given a TPO by the council.

The vendor, the the vendor's insurance company and the underpinning specialist that did the work all say that the oak roots can no longer get under the house to cause further subsidence as the oak's roots will not go that deep (3.3m), but my building surveyor says that its only a matter of a few years until the roots go under/through/around the barrier in their search for water. In your opinion, will the oak be able to circumvent the 3.3 metre deep root barrier? Any advice welcome! 

[The Professor]

So, prior to deciding whether to proceed with the purchase, I should get the drains around the rear and side of the house inspected by a CCTV survey to confirm no leaks from the drains (to ensure the roots aren't attracted to moisture), make sure there's a guarantee on the underpinning done and arrange an indemnity, as well as ensure my home insurance provides full cover.

Should I seek to get any work done to the oak tree to minimize the likelihood of roots circumventing the extra-deep underpinning? The tree is protected by a TPO (civic amenity as just visible from public highway), but the council's tree officer mentioned that the root protection area is usually only under the drip line of the canopy when I discussed the implications of building a rear extension.

[Chris at eden]

22 hours ago, Khriss said:

Root barriers are not the silver bullet for soil dessication problems  involving trees and the rewetting of clays can take a long time before the layer  'stabilises' , heave can be an issue too .

Not to mention, what he is describing doesn't sound like a root barrier anyway!!!

[Chris at eden]

18 hours ago, The Professor said:

So, prior to deciding whether to proceed with the purchase, I should get the drains around the rear and side of the house inspected by a CCTV survey to confirm no leaks from the drains (to ensure the roots aren't attracted to moisture), make sure there's a guarantee on the underpinning done and arrange an indemnity, as well as ensure my home insurance provides full cover.

Should I seek to get any work done to the oak tree to minimize the likelihood of roots circumventing the extra-deep underpinning? The tree is protected by a TPO (civic amenity as just visible from public highway), but the council's tree officer mentioned that the root protection area is usually only under the drip line of the canopy when I discussed the implications of building a rear extension.

Its a bit odd that the LPA have TPOd the tree.  If the tree causes further damage then this is an actionable nuisance and so work to mitigate the impact is most likely exempt from the TPO. 

 

Root protection areas are not relevant in this instance as the zone of influence is a very different thing to an RPA.  i.e. Zone of influence for Oak is 25m (as per NHBC) whereas RPAs can never be more than 15m if you are following the standard, bit more if you are offsetting I suppose but the drip line comment disappeared with the 2005 standard anyway.  TO is talking nonsense when bringing in RPAs though. 

 

I would recommend that you get a tree report if you haven't already. 

[Khriss]

Realy needs more site details Prof, sounds like all concerned have made a decent effort but having the job redone after 6 years ain't making this house look like a good buy. Am no soil engineer but does sound like significant movement have/are taking place, soil shrinkage can have many causes but I would take yr sights off the oak till more exploration is done. K

[The Professor]

Thank you for your comments. Seems like the TPO was agreed because although the present owner of the house wrote a letter of objection citing damage by the tree, it was not backed-up by any of the required evidence even though they must have had the DNA samples and insurer's reports.

Obviously, there's a lot to think about and explore further before signing the papers to purchase the property. On the surface its a lovely house in an ideal area, and vendors/insurers/underpinners advise me subsidence has been fixed for once and all, but I don't want to be involved in regular rounds of underpinning for the next decade and then have problems selling-on in the future.

I will get a tree report and some advice from a specialist in subsidence before making a final decision (I'll try not to default to blaming the oak Khriss - I do actually like the tree!) Thank you all for taking time to offer you advice!

[daltontrees]

19 hours ago, Chris at eden said:

Its a bit odd that the LPA have TPOd the tree.  If the tree causes further damage then this is an actionable nuisance and so work to mitigate the impact is most likely exempt from the TPO. 

 

Root protection areas are not relevant in this instance as the zone of influence is a very different thing to an RPA.  i.e. Zone of influence for Oak is 25m (as per NHBC) whereas RPAs can never be more than 15m if you are following the standard, bit more if you are offsetting I suppose but the drip line comment disappeared with the 2005 standard anyway.  TO is talking nonsense when bringing in RPAs though. 

 

I would recommend that you get a tree report if you haven't already. 

A couple of things to add. First the tree sounds like it's not in the Prof's ownership, so self-abatement under exemption may not be an option. Secondly, wilful damage (the cutting of roots) to reduce water uptake of the Oak is not covered by exemptions. Thirdly the cutting of roots to reduce wter uptake in the long term is a questionable solution, since if it is not accompanied by crown pruning the roots will grow back. Fourthly the TO's RPA comments were in the context of a proposed extension, not the subsidence damage, and could have been relevant.  It may be the Prof who has picked it up wrong and confused it with zone of influence.

I'm not having a go at you, Chris, just thought I'd round out the Homeowner's advice.

The issue is certainly actionable nuisance. If the tree owner won't abate it, he could be liable for the resulting damage. If he would do it, but can't becaue of the TPO, he should apply to have it allowed, and do it of he gets permission. If he applies and doesn't get permission, he should appeal. If he still doesn't get permission, the Council is liable to pay compensation for the damage.

[daltontrees]

I shoudl add, as I often have to, that if the tree is not in England, the aforegoing advice may be wrong. I am assuming it's in England, as no-one bothers to say so unless it isn't.

[Chris at eden]

1 hour ago, daltontrees said:

A couple of things to add. First the tree sounds like it's not in the Prof's ownership, so self-abatement under exemption may not be an option. Secondly, wilful damage (the cutting of roots) to reduce water uptake of the Oak is not covered by exemptions. Thirdly the cutting of roots to reduce wter uptake in the long term is a questionable solution, since if it is not accompanied by crown pruning the roots will grow back. Fourthly the TO's RPA comments were in the context of a proposed extension, not the subsidence damage, and could have been relevant.  It may be the Prof who has picked it up wrong and confused it with zone of influence.

I'm not having a go at you, Chris, just thought I'd round out the Homeowner's advice.

The issue is certainly actionable nuisance. If the tree owner won't abate it, he could be liable for the resulting damage. If he would do it, but can't becaue of the TPO, he should apply to have it allowed, and do it of he gets permission. If he applies and doesn't get permission, he should appeal. If he still doesn't get permission, the Council is liable to pay compensation for the damage.

No Worries Jules, no offence taken.  I skimmed the post quickly and missed the bit about the extension so my oversight really, apologies to the OP. 

 

I wasn't really suggesting cutting roots or causing wilful damage but if the subsidence reoccurred and was shown on the balance of probabilities to be down to the tree then mitigation works would be required whatever they may be, this would be exempt in my view.  That is realistically topping or felling, root pruning is a waste of time as the use of root barriers in not recommended by NHBC and the roots will grow back as you say.  I still think TPOing a tree with low visibility on a shrinkable soil and adjacent to a 1930s house (with previous subs issues) is just bonkers.   

 

There was a claim a few years ago (I forget the ref) where the applicant submitted evidence showing seasonal movement and the LPA refused inviting them the appeal.  They took some legal advice and did not bother with the appeal and instead went straight to putting in a claim against the LPA.  The LPA used the defence that the appeal route was available.  The applicant won the cost of underpinning as the court took the view that the LPA decision was wrong irrespective of the appeal.  Basically why should they mess about appealing the LPAs incorrect decision while damage is clearly occurring.  I would personally always go for appeal but the PINS can take up to 27 weeks to determine an appeal so that can be an issue if damage is on going so I kind of see the logic. It would probably be worth starting the ball rolling on both. 

 

My main point though was get some appropriate professional advice on trees, soils, the underpinning, and the value of the property and how it will be impacted by the underpinning.  Its not a straight forward purchase. 

 

Cheers

 

   

[Jon Heuch]

On ‎04‎/‎02‎/‎2018 at 10:34, The Professor said:

The vendor, the the vendor's insurance company and the underpinning specialist that did the work all say that the oak roots can no longer get under the house to cause further subsidence as the oak's roots will not go that deep (3.3m), but my building surveyor says that its only a matter of a few years until the roots go under/through/around the barrier in their search for water. In your opinion, will the oak be able to circumvent the 3.3 metre deep root barrier? Any advice welcome! 

This type of situation is often complex and the only test of importance is whether the building continues to move (& cracks)....or not. A property seller with any gumption will redecorate shortly before the house goes on the market with the hope that the seriousness of the situation can be hidden from view.......but does the redecoration reflect a stable house or something else? In the short term, you have no way of knowing - forget seeking "expert" advice, it won't really be of much use as you will get a range of views. What it might be useful to have in the medium term, but of no use to you now, is level monitoring (3-6 months worth of data) but this will only come to its own when we have a hot dry summer (that's when the property will be tested by the actions of the tree).

Your question to this arboricultural forum is whether oak roots will get below 3.3 metres; in natural soil in SE London, the answer is yes but there won't be a huge amount of activity at that depth. In disturbed soil, where a trench has been dug for underpinning, there will have been greater aeration and changed circumstances for root growth. Who knows what impact that will have had on rooting - none of us were there when the trench was dug and refilled - but if the tree is mature and not growing a lot the root growth should not be too vigorous (that's a positive factor). If the tree still has some potential to grow larger, there is a greater chance of the roots growing under the underpinning.

Your real challenge will be getting insurance; the current insurer should offer to continue cover which should include "subsidence, landslip and heave". If it doesn't, certainly walk away. If it does, compare the cost of insurance offered against a price comparison website cost for the same property where there is no subsidence reported. You will be stuck with the same insurer & that annual difference for life (or whilst you own the property!) & it could get worse if the subsidence re-occurs. You might be able to get an alternative insurance supplier but that will require a specialist broker (possibly ££££).

 

Next problem:.......(oh dear!): semi-detached house with your property partially underpinned.......a recipe for a disaster. The underpinned part of the property will be relatively stable, the rest (including your neighbour's property attached to yours) will be less stable so may continue to move if the oak roots extend that far...... A key factor will be the location of the tree relative to the two properties.

 

All I can say is proceed with caution and if you do decide to go ahead that the price you pay reflects the issues above; remember, when you want to sell the same questions may be asked, making it more difficult to sell. The only consoling factor I can give is that compensation may be payable by the Council for loss or damage that occurs AFTER they refuse any application to fell in the protected oak in the future (this is a complex timing issue and not a blank cheque for anything that happens). Councils don't give up their cash too willingly, rarely pay 100% of a claim & it typically requires both perseverance and the ability to wait a year or two (or much more) whilst the cogs of justice rotate.....so compensation is very much a consolation prize.

 

[Jon Heuch]

34 minutes ago, Chris at eden said:

 I still think TPOing a tree with low visibility on a shrinkable soil and adjacent to a 1930s house (with previous subs issues) is just bonkers.      

Welcome to much of London........