The Professor

Underpinning report says 'C30 grade concrete poured to form pins in sequence' - they excavated underneath the previous underpinning.

Here's a satellite photo of the oak in relation to the pair of houses. It is located at the edge of the dirt track used by the garages, owner unknown. It's not in anyone's boundary. The house nearest to the tree has apparently required more underpinning than the one on the right which I'm interested in buying. The trunk of the tree is approx 16m from the rear wall of the house on the right.

I have requested and received a lot of the insurance company and contractors' documents related to the underpinning work. The geology report shows that the soil is 'firm/mid-firm orange, brown mottled grey clay' from a depth of 40cm down to 3m. The deepest roots found in the bore hole samples were at 190cm. Do you think the oak roots could go deeper than 3.3m as the tree continues to grow in such soil? As suggested by others in earlier posts, I'd check that there are no leaking waste-water drains to attract them deeper than they'd grow naturally.

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!

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.

The sewage/waste-water/ drain pipe (I'm not sure of the exact terminology - the waste bath/toilet water feeds into it) starts at the rear of the neighbouring semi-detached and runs under the rear patio of the house that I'm potentially buying. The pipe then turns down the side alley of 'my' property down to the main sewer located under the main road at the front of the house. I believe that this waste-water pipe is actually the property of a Thames Water, as the next door neighbour's waste flows under the rear patio of my house. The house was built in the 1930's, so I expect that these waste-water pipes have always been there since the house was built.

Here's what seems to have been done during the second round of underpinning: "Establish the edge of the existing underpinning projection and excavate down the side, a trench 1m wide to a depth of 3.3m. Install spreader boards and accro supports to support the side of the excavation and provide lateral support to the underpinning. In an agreed sequence, excavate under the existing underpinning bays to a depth of 3.3m and remove spoil from site. Carefully shutter and pour C30 grade concrete to form pins in sequence. Shuttering to be formed 200mm beyond existing face and the pins poured to 200mm higher than the existing pins to al low for any shrinkage." Although the work has been described to me as a 'root barrier' the invoice from the company that did the underpinning simply refers to it as 'underpinning' - so does the building control sign-off certificate.

Thanks for your advice so far. There is a sewer pipe running under the rear patio which had to be rebuilt while the 2008 underpinning was done. The cast iron pipe was replaced with a plastic one and the access manhole brickwork re-pointed. I'm guessing that the original pipe may have been leaking and attracted the roots towards the house, but can't know for sure. The extra depth added to the original underpinning was described to me as a 'root barrier' but I'll try to look up some extra information about it and post it here in a short while.

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!