Possible subsidence and building work

[Zebra789]

In a bit of a dilemma and would appreciate advice from someone more knowledgeable!

We suspect we’ve got a bit of subsidence due to our neighbours having stupidly large trees close to the boundary. They’ve agreed to reduce the height of them and we’re waiting for that to happen.

We’re due to have some building work done in the next few months, having a conservatory turned into a proper extension (on the other side of the house from the bit I’m worried about). The foundations are already deep enough so there’s nothing involved with digging the foundations etc. We’ve been waiting absolutely AGES for our builder to be free and the conservatory is dreadful, leaking roof, changes temperature of downstairs horribly etc.

If we tell the insurance company now and they find that it is subsidence, will we have to put the building work on hold for a few years until it’s sorted? Or will we be able to go ahead? We’ve had these cracks for ages (we didn’t realise until recently that it was probably subsidence and needs properly looking at, I asked a builder years ago and he said it was nothing). I’m really worried that we won’t be able to do the extension, but equally worried that I don’t want the house to fall down if we leave it another few months before investigating it!

Widest part of crack is about 1mm I think (but this is after we previously polyfillered a similar size one). Cracks are pretty lengthy and along where the existing extension joins on. There’s a few in the render outside too that have been there for a few years also, I thought it was just poor render that needed replacing.

Any advice would be appreciated, I’m feeling really stressed about what to do next.

My experience of claiming for subsidence is that they only look at the part of the house which is affected.

They are very unlikely to underpin unless they have no choice; they will pay for the trees to be removed, might / should check the drains too, will monitor for 6-12 months to make sure the crack isn't moving any more and then will then fix the cracks by pinning brickwork if necessary and / or repairing plaster and redecorating. That's it. Only if they are forced to, when the problem recurs, would they underpin (£££££).

If you have an engineer engaged for the extension, perhaps s/he would have a look, though my insurance company reacted very quickly.

We suspect subsidence in our house, so much so that we’ve had a structural engineer out twice, paid privately because we didn’t want it on record.
we have it in writing that he thinks it’s historical movement and expansion and contraction through the seasons.
we still disagree as there are still signs of movement, however we also discovered that our drains weren’t properly connected up and had been leaking - this was fixed last year just before we started our extension. We have had further movement, but suspect it’s probably due to the ground drying out now the drains are fixed, so are watching and waiting. I do feel for you, it’s incredibly stressful but it did set my mind at rest having the engineer out!
oh, and as part of the engineer investigations with trial holes, we discovered the previous owner had our house underpinned and never declared it!

Even if you get your insurers invoked they tend to monitor movements for at least 12 months op so I. And see them doing anything drastic until they know it is defo movement. Have you had an independent surveyor come and look at it for you? Xx

But if you decide you need to claim in future, how will you explain away all this delay in informing your insurance company?

1mm crack I wouldn’t be telling the insurance company about just yet. I would measure watch and wait to see if it grows. You really need to start worrying when you have various of 3mm or one at 5mm. If it’s where the extension joins the house, it could be seasonal movement as the foundations could be different. Most houses have some form of cracks from seasonal movement/heating differences.

if your really worried maybe get a private structural engineer to have a look before insurance as once a claim (even if it’s not subsidence) will need to be declared.

by explaining exactly what I’ve said, our SE felt it was expansion and contraction and that we’ve continued to monitor following fixing our drains - but now suspect it’s something more sinister, and hence contacting insurance. We have only done what they would in the first instance. Having already undertaken all of this should only serve to strengthen any claim.
although I’ve no idea what they would actually do given that we’ve already been underpinned!

I thought about getting a surveyor to look independently, but then I thought if it was subsidence we'd need to declare it to the insurance company at that point. I'm worried about shooting myself in the foot in terms of the upcoming building work more than anything! We've been waiting for over a year.

We're going to have to look into it at some stage, definitely, but I'm just dithering about whether we need to do it now (DH and I both agree that the cracks have recently got a teeny bit more pronounced on both the render and inside, probably due to the dry weather) or whether we could hold out until after the building work before noticing it...

Frustratingly we've already done all the planning side of things with the structural engineer and architects otherwise I'd have asked them their opinion! The cracks were definitely visible when they were here and no one said anything, which I suppose is reassuring in itself.

@Blue2021 That's really reassuring thank you - the internal ones are definitely around 1mm in diameter (but pretty lengthy). The ones on the render outside it's hard to judge as they're second floor height, we just thought the render was crap (it is generally and needs re-doing). I'm going to have a proper look at them tomorrow, but I'm pretty confident that they're not that wide (second floor though, so hard to judge). The thing that reassures me is I KNOW they've definitely been there for years (which we put down to the crap render), one has just got a tiny bit longer on the extension recently. If it wasn't due to the proximity of stupidly large trees I'd probably put it down to seasonal movement and the recent heatwave. We didn't build that extension, so I don't know much about it, beyond knowing it was signed off by building control as I have the paperwork somewhere.

I doubt your SE would’ve taken note of the cracks, if ultimately he was there for your extension. You would have needed to specifically point them out. I’d be tempted to get them back in - if nothing else it may give you peace of mind.
trees will be thirsty with the recent heatwave - your SE visit may give you ammo to persuade your neighbour to get them removed, but it’s likely that as the roots die back there could be more movement.
a conversation with an SE will be no bad thing before contacting the insurance company, in my opinion.
I know what you mean about your extension by the way! I could have weittten your post 3 years ago. We went ahead and no regrets - if you can count living on a building site for 2 years with incredibly slooooow progress (self build) as no regret!

Neighbours are intending to get the trees to a more manageable height, I personally think they need to be removed entirely though, but I think this is a reasonable first step. I'm more worried that I'd need to immediately contact my insurers and get the ball rolling if the SE says it's subsidence, although I suppose he won't tell them and it's up to us really how we proceed with that information isn't it...

Oh gosh, that sounds super stressful! I don't think I could cope with it for more than a few months. I think I've only just finished hoovering up all the dust from our last big project a fair few years ago now!! Our conservatory is just dreadful, the roof leaks and it makes the downstairs baking in summer and freezing in winter. I've been SO excited about it becoming a permanent extension! I know it's not the end of the world but I'll be gutted if we have to pause it for a few more years.

Any pictures of the cracks ?
1mm could easily be down to the dry weather and shrinkage in the ground, it’s been very dry /hot for most of this year.