subsidence next door - asked to remove hydrangea

[railingsandsilver]

Live in a terraced house in Bristol and have a lovely mature climbing hydrangea on my exterior wall.

Unfortunately my neighbours have bad subsidence (our place is safe, as was underpinned years ago). Their insurers have 'recommended' that we remove our hydrangea - but their monitoring has shown no evidence of hydrangea roots under neighbour's property, and their report specifically says that vegetation couldn't be determined to have caused what's going on. It seems to be precautionary at this stage.

My plan is to say that I don't believe it's necessary to remove it now but if it shows as a clear factor at a later stage we'll reconsider. But I'm a bit spooked by the 'if you don't follow our instructions, we could hold you liable for costs' wording on their letter. I know insurers like to do this to intimidate and can't legally make us do it if it's an unproven cause.

Does anyone have any experience? Do I just hold my nerve? TIA

Don't overeact OP. I'd do nothing.

It's a hydrangea, it's on your land, it's a recommendation only. Insurers would ideally have no vegetation anywhere near a house to reduce their risk

The remedial measures that your next door neighbour is taking (underpinning presumably) should mean that any further risk to their property is effectively zero.

It has put her on notice - I’ve not told her to remove anything but the advice given here is nonsense.

you don’t know what the evidence shows because the OP hasn’t really mentioned much beyond saying roots weren’t discovered. We don’t know how lengthy the investigations were or anything else.

It doesn’t sound like the hydrangeas are the sole cause regardless but if the house keeps moving and everything else has been removed, then the OP can expect to be contacted again but this time for costs of repairs added.

I thankfully don’t have to deal with subs claims very often as they are beyond tedious.

that must be a huge hydrangea! the roots have to go deep to enable the soil to dry out enough for the house to move.

We have a very large climbing hydrangea up against the house. It has been there 30 years and live in an area where subsidence can be quite common in older houses. No sign of it causing any issues and no noticeably dryer soil around it (I love gardening so monitor soil conditions closely, plus DH works in this sort of area). Honestly, I think they are pulling a fast one. Roots just don't go down that far/that wide. I would get a second opinion and some legal advice before doing anything. It is the insurance company's responsibility to sort, not yours. And notify your insurers.

I’m a geotechnical engineer. My job was once to design foundations and account for trees and shrubs.

If you have very shrinkabke (clayey) soil, a hydrangea could impact foundations - but removing it could also cause ground heave, which will also damage foundations. Clayey is foil that you can roll into sausages without them cracking.

I would guess though, that the cause of your neighbor’s subsidence is whatever caused your house to be underpinned.

Some Victorian houses were built with a layer of bricks straight onto the clay mud and have zero fountains/footings. We don't know of the age of your property or the OP's - or whether either house has foundations.

Yep Civil Engineer here and I was thinking the exact same but with much less expertise than you of soil.

Also as I said upthread because the OPs house was weaker before underpinning then her house was expressing the subsidence and now that it has been strengthened that will mean the neighbours house is the weaker one and therefore expressing the subsidence because all of the houses are linked together it has to be expressed somewhere.

It probably allows the insurance company to say we will now have to re-assess the claim in 12 months if you cut down the hydrangea, to see if it makes a difference.

A quick google says climbing hydrangea are highly unlikely to cause subsidence the root expanse is too small and too shallow compared to the trees that usually cause subsidence in shrinkable clays.

Edit: Also retired Civil Engineer that worked in geotechnics and at one point specifically in shrinkable clays.

Hence why recommending a second opinion.

@Ellensapple What you wrote is garbage! Subsidence is where the soil around the foundations shrinks. Or is washed away. This can be gravel soil that is not stable or frequently, clay. It’s often a case where there’s no rain, the clay shrinks. This is turn allows shallow foundations to fail. Cracks are then visible in the building. The soil can dry out because a tree is drinking too much water and is too near the house. Large mature trees and especially willows, drink a lot and have very extensive route systems stretching a very long way. A shrub is nothing like a mature tree!

Heave is completely the opposite. It’s where too much moisture is retained in the soil. Can be via water retained because trees have been removed and sometimes leaky pipes or a sump of water that collects under the house. Heave is expansion of the soil under the foundations and pushed the walls up and outwards.

The op should ask for evidence that her shrub is doing anything! A few trial pits will establish what’s going on but it’s either mature trees or dry soil that’s moved and shrunk.

DH is a structural engineer and certainly knows about soils. You cannot design foundations with no knowledge of the soil! You need to know about trees too!

But you need to talk to your insurers to cover yourself against potential future claims.

Whether or not hydrangeas are thirsty or potentially problematic plants is a separate issue.

Comply with your insurers’ requirements.

Climbing hydrangea do not have invasive roots that would damage foundations. They have aerial roots that enable the plant to cling onto brickwork.

That langage is just designed to frighten you @railingsandsilver and is clearly being effective.The insuraner cannot unilaterally hold you responsible and you are well within your rights to require some evidence. You are also correct that insurers will do virtually anything to delay or avoid a payout.

I wouldn’t expect that type of plant to cause such damage, it is not a stand of massive willow trees. Do you have any evidence of what causes the subsidence in your own property and being able to say it was x, not plant systems, may be helpful.

Hold your nerve. I’d be asking for investigations and evidence such as soil analysis and specific root identification before anything else. Simply having a climbing hydrangea on a shared boundary would not usually be enough evidence.

A hydrangea might be ‘thirsty’ but it’s not considered a high water demand shrub or tree that would cause shrinkage.

I’m a building engineer and have overseen dozens of subsidence cases. I’ve never once seen one attributed to a hydrangea.

Hydrangeas normally have shallow roots and the reason why they are thirsty is because they have large leaves and the roots can’t suck up water quickly enough.
I would be surprised to find out that your plant is the cause of their subsidence.

@Pansykavalier You absolutely do not speak to your insurers!! They have already paid out and I’d bet a lot of money this has nothing to do with Op. Neither will there be a claim so stop scaremongering. You don’t know what you are talking about!

OP you won’t be and can’t be held responsible for the damage that is exists now because you didn’t have the requisite knowledge. It is only any additional damage which is attributed to your hydrangeas from now on (because you do now have some knowledge) that you’d be liable for IF movement continued after they’ve remove whatever else they intend to remove. They probably will keep monitoring as they will want to know if the movement has stopped before they repair. You’d only ever be responsible for any additional damage caused after you’ve been notified. Do you know what other trees etc they are going to have to remove?

Thanks for the education. You should take it up for a living like I did. We are crying out for Civil Engineering lecturers at my university. You do need to have a decent level of experience in industry and a PhD in engineering and then you can make money out of lecturing other people like I get to do.

Heave causes subsidence in the same way that freeze thaw causes rock to fail. In heave the soil holds onto the water and then it dries out in drier times. The action of heaving and drying out weakens the support to the foundation and damages them.

Have you ever worked as a structural engineer? DH is FICE, FIStructE and F of another one! This is the real world where the cracks produced by heave and subsidence are different! Heave is pushing up the foundations and that causes the damage. What it does afterwards is somewhat besides the point. The damage is done. Have you ever inspected a house with heave? Tell me what you saw and why it was different from subsidence damage.

My DH made far more than any lecturer thanks. He did the work.

I would dig out a trench on the boundary, document for roots and install a root barrier.

Where did the OP state that her insurers have already paid out? Your post doesn’t make any sense. In this situation it makes total sense for her to log this with her insurers, in case of future litigation against her.

If your house had underpinning, it means the issue is the soil, not the hydrangea. I live right next to a big park and there are huge trees growing a few metres from my house. The house (and every house on the road) had underpinning done in the 90s due to being built on clay soil. The house had no subsidence issues since then despite all of the huge tree roots under it. If your neighbours do underpinning properly, their house won't be affected by a silly hydrangea

I’d remove my plant .
Could buy another and pot it up
This is someone’s house .

@Pansykavalier A poster says the op should notify her own insurance because the neighbours instance might counter claim. Did you read that? I’m suggesting the op does nothing of the kind because she’s almost certainly not contributing to subsidence. What is happening to next door is not happening because of her plant. The insurers of next door should pay for ground investigation and trial pits to see what is happening to the ground around the foundations and not take wild guesses about a hydrangea. So my post made perfect sense . The op should sit tight until proof is ascertained.