Subsidence

[Yukduck]

We bought our property 4 years ago. The survey passed the property with flying colours, no issues. Within 2 years we had cracks appear in our back walls, internally and externally. We told our insurers and they suspected subsidence so the cracks were monitored for a year. In this time our soakaways and drains were renewed (to eliminate this as a cause), and a large neighbour's tree taken down (said to be the cause). The loss adjusters did not really know what the cause was when we asked for a difinitive cause, but said it had stopped moving.
We moved out for 3 months and the walls were re-built internally and ceilings and walls replastered to half the house, back windows and doors replaced. We moved back in.
Now, over the past year, the cracks have re-appeared in the new plaster. It looks like the insurance company, the loss adjuster and the builder did not get to the bottom of the cause. Some of the cracks are in the same place.

What happens when subsidence repairs fail? We have let our insurers know and also the loss adjusters and we are waiting to hear back at the moment. We just don't know what the next steps could be and are a bit worried.

Possibly it was not subsidence? Unless you had a report from a structural engineer you may not have had an accurate diagnosis. Loss adjusters tend to be finance driven and many are frequently not qualified or sufficiently experienced to make any judgement and builders likewise.

Are the foundations of the back wall suitable for the soil? Is there now "heave"? This is where the soil is too wet and swells. Happens with clay. It pushes the walls about if the foundations are too shallow. Would have thought this would be unlikely with underpinning but the removal of the tree has allowed water retention in the soil - the tree is no longer drinking it! The cracks indicate movement but if they are not serious, are they standard shrinkage cracks that you get with new walls? If they have split the bricks,you need it looked at.

Get a qualified Structural Engineer to come and look. Someone who has experience of this type of problem! Not a surveyor either.

How old is the house? Was it a new build?
Agree re structural engineer, it could be tree-related, mining related, poor build quality, drainage related depending on where you live and the age/type of house.

Likely to need geotechnical assessment as well as structural (I am a geotechnical engineer). Depending on the clay content of the soil and the type of tree, cutting it down could aggravate the situation.

Is it a new build or older house?

An engineer will commission soil tests. It is cracks in the outside walls that are critical. Interior cracks may be the walls drying out. Are there external cracks?

Thanks all. The soil is more sandy than clay. Pine trees grow well in local parks in our area so I am guessing we have sandy soil (New Forest area).
Our home was built in the 1960's on a gently hilly area, an estate built on the site of an old orchard and chicken farm, so quite fertile soil. We are detached (most properties are on our estate).
Neighbours who noticed the builders at ours told us of their own historic subsidence issues, so it is not unknown in our road (but first we knew of the general problem in our area).

One or two neighbours said the same - our homes did not have deep enough foundations when built.
It really is a worry. We had no idea as the survey highlighted no issues.
I am not sure how much a structural engineer would cost, and even if our home is insurable if we pursue this matter.

Sorry, forgot to say cracks are on the outside as well as inside.

The cracks are diagonal and stepped along the pointing through the brickwork on the outside. On the inside walls they are bigger at the top of the crack than the bottom. This is the same as the first time round.

Slightly different this time as it is the side of the property from back to front that is affected. Last time it was mostly the two back rooms.

No underpinning was done or soil samples taken the first time. I was surprised at this as I was told someone would visit to take a soil sample in the early weeks but it was called off as unnecessary and metal tell-tales were stuck on internal and external walls for a year instead.

I am wondering if not enough was done the first time round. I am really hoping there is still something that can be done.

Geotechnical engineer here too - what kind of tree was taken down, how close was it to the house? Does your soil drain well?

Soil mapping indicates that there is a potential for shrink-swell clays in the New Forest area, so a combination of shallow foundations, swelling soil and the removal of a tree (especially one with a high water demand) could have resulted in heave causing the cracking.

It should be relatively straightforward to have a test pit dug to examine the foundations and to take soil samples to determine the swelling potential of the soil.

If there are soakaways then how likely is it to be on clay? I guess it could be a surface layer and the soakaways go to something more permeable underneath.

Ultimately though, they didn't correct the cause of the movement as it has moved again. I would have thought it was time for underpinning.

whatscoming older soakaways can just be a large pit filled with builders rubble to store water and allow percolation into surrounding soil - clayey soils would need a larger pit, and as you say they may be dug deeper to penetrate a more permeable layer.

Thanks for coming back to me again.

The tree was a cherry tree. The neighbour planted it 50yrs ago. Size 40ft high x 50ft spread. The trunk was approx 2.5ft circumference. It was planted central to the back fence of our property (she is our bottom of garden neighbour). The branch spread was the whole width of our garden and gave us and her privacy.

She removed it at the loss adjuster's request approx 2yrs ago, just before monitoring started.

There are no other trees nearby now this one has gone.

The soakaway was a brick honeycomb large circle just under the back lawn around 15ft from the house. It looked a bit like a buried wishing well with a wooden circle lid on top just under the lawn. It was to take the roof water away from the roof gutter and was in good condition. The underground drainage pipes that lead to it were replaced as they leaked a bit just to eliminate them as a cause of the back wall cracks.

I had subsidence, sympathies, it's horrid and you feel so out of control. My insurers got a company to look at all the drains and to take soil samples from the front and back of house so sounds much more thorough than yours. I was also told that if it recurred within six years it was part of same claim, not sure whether that is industry wide practice. I think I would also be tempted to get advice independently to think about next steps and what you should be saying to insurance company to get it properly remedied. My understanding is that your insurer should continue to cover your property though that is convention rather than written into any law or regulations and I don't know how reliable that is.

I think you do need to consult your insurance policy regarding a claim but you must not just go with a loss adjuster and a builder. A structural engineer will get a soil appraisal and get the house underpinned or other remedial work and ensure there are adequate foundations for the ground conditions. You don't need to engage the separate professionals. I do hope the insurance will pay - they should! If the people who advised you last time were their recommendations, they have a responsibility.

I cannot believe it was not underpinned before actually, if they thought it was subsidence. Sounds like a money saving exercise to me. If the foundations are too shallow it is necessary to put this right and a structural engineer will know what depth and construction is needed or how to underpin.

Slightly off topic, but we are on clay but have a soak away into the Chalk below. If the soak away is working, it could be removing the rather large cherry has caused the latest problem, combined with insufficient depth of foundations.

How much does a Structural Engineer cost? DH is one - he's expensive but he is the senior partner of a fairly large consultancy. You won't need him! They are the equivalent of hospital consultants, for buildings, but cost depends how much work is involved and experience of Engineer. A small company with experience in this field is just fine. They will advocate for you with the insurance company as well and you will get a better resolution and it will give you peace of mind. You do need this house to be saleable at some point. It's a no brainier really. I feel you were fobbed off before by people who were perhaps ill equipped to understand the problems and the ones created by tree removal. Your surveyor should also be - shot!!! Fancy missing this in an area where remedial works have been carried out. The insurers may want to know about that.

Years ago my husband had to oversee the demolition of a house that was 2 years old due to heave. 8 willow trees removed by the builder and the site was on the edge of a small brook. Clay soil. You could see right up to the bedrooms when standing by the lounge walls. The walls just fell apart like a deconstructed box. Not saying yours will do that of course. Foundations are important though! Engineers are the best people to design them and act on your behalf!

Thankyou.
I am so worried we will have to move out again. It was incredibly stressful last time with everything in storage and our animals in kennels/cattery and our family, friends and grandchild not being able to see us much as we were so much further from them in alternative accommodation.

Bojo underpinning will only be done where the problem can't be sorted out by removing the cause - in my case it's keeping a tree cut back. I think I read only 15% of subsidence claims result in underpinning

The mature cherry tree at 12m high should have been a minimum of 9m from the house (0.75 times mature height). How far from the house was the tree?

The cherry tree was approx 50ft from the house.

50 feet = 15m, so even in high shrinkage soil that should have been far enough away to have a minimal effect. You said your neighbour had a problem with shallow foundations - do you know how deep they are?

I would get a full structural survey by a qualified structural engineer. He may check the walls for sufficient wall ties etc. It will cost but it sounds like you may have to make a claim against the builder so you will recoup your loss/fee long term hopefully.

I do not know actually how deep our foundations are but one of our neighbours who had subsidence (two doors down) did say that our homes were built with less than the usual meter foundations. He said that this was found to be his problem. His was underpinned a year or so before we moved in to the road.

The builder who did the work at our house worked to a schedule of works set out by the loss adjuster. The builder removed some of the internal walls in the back rooms (the worst affected) and rebuild them with metal straps, then replastered. Double glazed windows and French doors were replaced in the back, with strong integral lintels which we were told would also stabilize the back wall.

The cracks are back. Almost as big as before and like the brickwork behind the plasterwork has "jumped" just as it did before.

I never felt it was the tree, our drains or our soakaways. Our soil is sandy loam and drains well. Looks like the cause was never found and the problem remains.

Chances are a new structural engineer coming in will want to do more monitoring. It does depend on how big the cracks are though and whether there is an obvious fault causing them.

Like Informal said, 15m is a long way for the tree to have had much effect. I wonder whether the ground is simply inadequate, onto fill or similar, and they need to go deeper to decent ground.

If the neighbour's house was built at the same time then it most probably will be the same problem. Can you ask them nicely for their report?

That is a good idea. I will ask our neighbour if they are happy to let us see their report.

We never had one. It was all done on the loss adjuster's spec of works for the builder.

Did the loss adjuster have suitable qualifications or experience one wonders? It is the loss adjusters fault. The builder just did what he was told!

The loss adjuster should have PI insurance to cover this sort of thing.

Subsidence is where the foundations are not holding up the house, for whatever reason.. This allows the walls to move unevenly.

Keeping a tree cut back means it drinks less water but after underpinning this should be neither here nor there. The underpinning should have taken account of trees.

Where clay soil is excessively wet it expands and that is heave. It pushes the foundations upwards and the walls outwards. This is more likely to happen where pipes are leaking and saturate the soil. This is not really subsidence. Subsidence is shrinkage in the soil because it is dry. The walls and foundations settle at differing rates resulting in cracks. We get subsidence all the time in draught conditions. Underpinning is not cheap so loss adjusters avoid it. That doesn't mean to say it didn't need to be done though! It is money driven.

Years ago ordinary builders would not have had foundations designed properly. They just did what they thought best. You only have to look around lots of housing estates now to see garden walls that are not designed properly. Where we used to live, several blew over. Same problem - not designed properly and cheap construction.