Neighbour's trees making our house crack? What should we do?

[mrskbpw]

We live in a semi-detached 1930s house. It's got a single-storey extension on the side, where a garage would be (in fact, I think originally it was going to be a garage but the people who built it changed their minds). The extension is a bedroom/study at the front and a shower room. We've noticed recently that the whole extension seems to have shifted. There are cracks appearing in the walls and worryingly, the door frame on the bathroom door is no longer flush against the wall.

Our neighbour's house is set further back than ours. Between our house and his drive is a row of conifer trees - no more than 2m (probably less actually - some could only be about 1m away) from the wall of our extension. Apparently, they used to be small but now they're huge - higher than the extension - and have never been trimmed since we've lived in the house (since Feb 2009). I'm wondering if this is what's causing the cracks?

Anyway, do any of you wise people have any knowledge of this stuff? Could it be the trees? What should we do? Should we call our insurance company or is that something we should do later? We do have builders coming in a few weeks to do some different work, so we could ask their opinion, but I'm actually worried about leaving it now we've spotted it.

[Pootles2010]

No experience (apart from Sarah Beeny shows!), but could you have a word with your neighbour?

Are the cracks straight or diagonal? I'd definitely ask your builder, if they don't know, ask insurance.

[dexter73]

I would phone up your insurance company and tell them about the cracks. They will probably send someone out to have a look at them and see what is causing them.

[fapl]

I would do as much investigating on your own as you can before you call in the insurers.

Do you realise you have to declare subsidence when you apply for house insurance and it can really increase the premiums you pay? Also if you ever try to sell your house you will have to declare a history of subsidence which may put some buyers off. If it is still minor at this stage, try and figure out what the cause is and deal with that, then monitor it for a while. If damage at this stage only requires redecoration, get people in and pay for it yourself rather than go through your insurers. There is usually a £1,000 excess for subsidence claims anyway.

[Pendeen]

Are there any signs of cracking in the house or are they only in the extension?

[Cinders22]

We have a number of cracks on our concrete driveway and recently called a workman to give us a quote for it being redone. He said it was our neighbours conifer tree causing the damage, he said the roots can be as big as the tree. I had a word with our neighbour, I explained an expert has said it was the tree and that we could not have the driveway replaced currently as it would just happen again. Our neighbour was not happy, he actually had a tree surgeon come round and assess if it was his conifer that was causing it and found that indeed it was. Fortunately our neighbour has now cut the tree down to prevent further damage to our property.

So, my advice would be to ask a builder to come and assess the damage and ask him what could be causing it. If it is the trees I would firstly speak to your neighbour, whilst I do not believe they would be responsible for paying for your repairs, they may agree to cut down the trees and prevent further damage.

[mrskbpw]

Thanks for all the suggestions. The cracks are only in the extension - not in the main house. The extension is the part of the house right next to the conifers though, they run right alongside almost the whole wall. And actually, there are no cracks in our kitchen, which is also extension, but has no trees next to it.

Flipping heck - it's all extra hassle and expense, isn't it?

[minipie]

As fapl says I suggest you don't call the insurers until you've tried other angles first.

Are you on clay soil? If not, it's less likely to be the trees causing it.

I think that your neighbours can be liable for further damage if you ask them to remove the trees and they do nothing about it (as long as you can show it was the trees that caused the damage).

We have recently got our neighbour to remove a large willow tree that we think was causing movement under our house. However we did have a surveyor's report which said that it was likely to be the willow causing the issue. So I think you may need some kind of similar "evidence". All extra expense sadly yes.

[Pendeen]

I asked because modern foundations are usually deeper than those of older buildings and thus (usually) less prone to movement.

From your description the trees sound a possible candidate however the whole subject of movement in buildings can be very complex. I'm an Architect not a structural engineer (so not an expert in the field) but I know that often more than one factor is responsible for movement.

You say the extension was built before you moved in and the trees were fully grown yet the cracks are only just appearing? Is the ground by the extension often wet or after rain takes longer to dry out than the rest of the ground?

[Mammonite]

For it to be trees, you need to be (1) on shrinkable soil - usually a clay and (2) the structure is on shallow foundations and the cracks have appeared as the trees have grown bigger (or been cut down). So a new extension next to mature trees may not subside, but young trees could cause subsidence as they get bigger.

Drains, weak soil or overloading can all cause settlement as well though.

Can you work out from this what your soil type is (both superficial and bedrock) and say roughly where you are in the country? I could have a stab as to whether it's an area known for this problem.

See also this publication.

[mrskbpw]

I knew you'd all be clever on here. From that map (thanks Mammonite) it looks like we are in a pink bit - clay sand silt gravel. Another map I looked at says it is "slowly permeable seasonally wet slightly acid but base-rich loamy and clayey soils". I'm not completely sure what that means, to be honest. We are near Orpington - SE London/Kent borders. The extension was built in 1998.

We moved in in Feb 09 and our neighbour moved in about six months earlier.

The trees were, I think, always kept quite small by the previous owner of our neighbour's house. In fact, originally there was only one tree, at the front. But the two neighbours fell out and so the lady who lived in our neighbour's house planted more to annoy the people who lived in our house. (It's certainly annoying me - well done, her!)

Our neighbour has not touched/trimmed them since we moved in, so they've grown pretty large in those three years. We've had to cut them back a lot where they've been growing over our fence and on to our drive. I can't see the ground next to the extension as the trees are so big, they cover it. I can't get into the gap between our house and his trees.

[Mammonite]

Is that what the map calls "Head", believe it or not that is a geological term for soil? South east London is well known for subsidence problems on the London Clay, which is quite a large area, but you can have localised issues with clay deposits which tend to accumulate in small valleys too. The sands and chalks are not normally subsidence prone. However your trees might be so large and close that it's the roots themselves causing the problem regardless of the soil type.

I don't think there's an easy answer. You could try asking your neighbour to keep the trees cut back and see if the cracks close up again. You could ring your council and ask to speak to someone about nuisance high hedges. You could contact a few local structural engineers or surveyors for quotes to come and have a look and diagnose the problem. If the cracks are getting big enough to fit a pencil, say, you do have cause for concern.

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