What is subsidence? what causes subsidence and how to fix it

Simply put, subsidence is the result of a building slipping downwards into the soil. The consequence of this action is that certain parts of the property will drop more than the rest, causing the familiar symptomatic cracks down the walls.

Because of similar signs of problems, subsidence is often confused with the effects of heave or settlement:

• Heave is essentially the opposite of subsidence, where the soil around the foundations swells and pushes the walls upwards and outwards.
• Settlement is the natural process of the foundations for a newly-built property (or extension) squashing the soil to a natural final resting point, which causes the building to drop slightly.

There are several potential origins of subsidence that will help give any homeowner a few pointers to guide them towards the origin of the structural problems:

• One of the most common causes of subsidence is created by the location of trees. While a nice addition to any garden and an important source of recycled carbon dioxide into oxygen, it is the tree's roots that create a problem by drawing moisture away from the soil base around the foundations. This creates a void into which the building slips.
• Another likely culprit comes from clay soil. Because of the soil's structure, it is usually dense with water, depending on the water table. When that soil dries out, voids are created around the foundations which then cause slippage of the building above. This can also be attributable to a spell of drought, when insufficient water is held in the ground, as the sun's heat draws out the moisture from the clay.

Note: the opposite effect, where the ground is swamped with water, particularly in continuously raining seasons, the clay soil is plumped up and expands, creating a source of heave.

• Although it might not be obvious, leaks from domestic piping orthesewerage system can wash away the important soil around the foundations.
• Anywhere that is located near to currently active or prior mining works may be susceptible to subsidence, where the shafts cave in and create sinkholes near the property.
• It's also worth considering the building's age, its construction methods and materials, the adequacy of the foundations for the building size, and the poverty of the groundworks as a whole, since these all could point to the faults that create the perfect states for subsidence to occur.

The less common occurrence of landslide or landslip would be a possible cause of subsidence. This is where the ground surrounding the building's foundations shifts away, a situation that is most frequently found where the property is on a higher level.

Subsidence is always going to be a worry if you think you might have it, not the least for the cost of the remedies required to sort it out.

But it's important to identify whether it is subsidence or a simple case of natural settlement, which is a far less serious problem.

Most experts will point you towards the following symptoms to identify:

• New cracks appearing in walls and ceilings that are greater than the thickness of a 10-pence coin (3mm)
• Doors and windows sticking where they weren't a problem before
• New unevenness in the floor, particularly if it angles towards a corner of the room (try rolling a marble across the floor to see where it stops).
• A continuous widening of existing cracks, with a greater width towards the top.
• Cracks appearing at the corners of windows or doors and, again, especially where they are wider at the top than at the bottom.

If you are concerned about the existence of subsidence - old or new - you'll need to call in professional assistance to identify conclusively that your symptoms are caused by subsidence, as well as providing a clear plan for the problem's solution.

Structural survey

It is worth talking to a structural engineer, as well as your insurance company, to confirm what the problem is and how long it will likely take to resolve it.

What the surveyor will provide is a Structural Survey document, which differs from the usual Building Survey. As the name suggests, the Structural Survey concentrates solely on the structure of the building under review, while the Building Survey focuses on the entire property.

From this, the surveyor will visually check the symptoms, before going into more detail to confirm the source of the problem and verifying that it is an issue of subsidence. 

They may not immediately suggest that work start to resolve any problems, because they may require any of the following:

• Monitoring of the symptoms over an established period of time to clarify the cause of the subsidence (and whether the problem is worsening).
• An additional geographical survey to verify the status of the surrounding ground and its constituents.
• A drainage survey to confirm whether broken drains are the source of the problem.

When the surveyor has identified the source(s) of the subsidence problem, they can then confirm the remedies required to resolve it.

Underpinning

One of the most familiar terms connected with sorting out subsidence is underpinning. 

However, underpinning is really only used in the worst cases, which the Royal Institution of Chartered Surveyors (RICS) confirms covers fewer than 5% of cases. In one sense, this is fortunate - certainly for the other 95% of cases - because underpinning is a very expensive solution.

The process of underpinning is a construction method designed to strengthen the base of the footings of a building. Underpinning is usually managed by either strengthening the soil around the foundations (to replace any erosion that might have occurred) mixed with a strong resin that hardens around the footings to prevent future erosion. 

The more familiar method is for the contractors to dig away the soil (while supporting the building) and filling the void with concrete.

Management of trees

Trees are one of the most common causes of subsidence as the plant's root system reaches out to seek sources of moisture. As the water source dwindles, the soil dries up creating voids into which the affected building drops.

It therefore makes sense to manage the trees on or near your property to prevent the reduction in ground moisture.

The Association of British Insurers (ABI) provides a helpful table of guide information regarding the safest distance of planting trees from the nearest building. Note that this can be the main property or any outhouses with foundations, but must include the proximity of any of your neighbour's buildings.

The ABI list of the most popular trees, not intended to be exhaustive, are:

Source: Association of British Insurers

Note: This information is for guidance only

If you suspect that a tree or large plant might be creating a risk of subsidence because of how near it is to the building, you might want to consider its removal.

However, you should consult a structural surveyor to confirm that conclusion before uprooting any trees. You should also contact a tree surgeon to assist in the process of its removal once the surveyor has confirmed that course of action to prevent future or additional subsidence.

Removing trees, even if there is no evidence of subsidence, can also create problems, including subsidence itself or heave, since the source of the current moisture management is removed.

Before doing any work on trees on your property (or in combination with neighbours), you must also consider whether any Tree Preservation Orders (TPOs) exist on the plants. If so, you will need to obtain written permission from the local council before doing anything to them. 

Water capture

Where there is a problem with underground leaks, you should consult a plumber or drain specialist to identify the source and apply a suitable remedy. If it has been ongoing for some time, it might also be worth instructing a structural surveyor to confirm the status of any current subsidence or to provide their opinion and guidance on any likely future problems.

For the occasions where excess water is driving off the building and is either currently eroding the soil around the foundations or is likely to be a problem in the future, then you should get a specialist in to check over the rain management. If it is not as serious as that, you might wish to invest in water-butts to collect the rainfall (which is also a useful solution to help water the garden in drier seasons).

When it comes to confirmed subsidence, there are a few questions that you might have about your insurance and the ability to sell an affected property in the future.

According to the ABI, these are the most frequently-asked questions

• Does my insurance cover subsidence? - According to the ABI, a standard home insurance policy will provide cover for damage created not only by subsidence but also the effects of heave and landslip. Usually, the policy will have a stated excess (the amount the policyholder has to pay as part of the cost) of around £1,000, but, the ABI also notes, for properties which have already had subsidence problems, that excess value will almost certainly be higher.
• What is not covered by the insurance? - The ABI suggests that you should look at the terms of your policy, but the focus is on the main structure and the outbuildings. Generally, the policy will not cover damage to garden walls and patios, unless there is a direct impact on the structure or any of those outbuildings. Additionally, your policy might not cover for damage created by poor building practice, which means your only recourse would be to contact the builder.
• What should I do if I think there is subsidence? -The primary advice is to contact your insurance company as soon as possible, because subsidence cases can be quite complex and may take several months to resolve. Your insurance company will take you through the steps you need to take. In addition, they might appoint surveyors to assess the damage and what remedial action might be necessary. Note, too, that one possible action might be to simply watch and wait to see if the problems worsens, which means the solution may take months. 
• If I have made a previous subsidence claim, what happens to my insurance? - Because of the significant cost of fixing problems with subsidence, it is highly likely that the premiums for your policy may well increase. It will also help if you have involved your insurance company from the beginning and the work has been completed to their satisfaction or under their own direction. There may also be instances where your current insurer will no longer be prepared to accept the risk, and you'll have to look around for other policies that will cover you. Whatever your particular position, you should discuss your concerns with your current company and they will be able to give you the necessary guidance.
• If I'm buying a property that might have had subsidence, how will I know? - The TA6 conveyancing form (also known as the Property Information Form) is the key document. You should receive the TA6 from the seller's solicitor via your own conveyancer. The TA6 must, by law, cover everything that has happened to the home you're buying, including any works to repair damage from subsidence. If your seller has insurance cover currently, and you still want to go ahead with the sale, you could ask for the insurance company details and discuss your policy options with them - if they are currently insuring this structure, then it follows that they are likely to extend the policy to you when you complete the purchase.
• If I'm selling and have had subsidence, what happens? - The first thing is that you must be completely open and honest about everything (to your certain knowledge) that has happened to the home, including subsidence. All this information and details are completed on the TA6 conveyancing form, which you should complete as quickly as possible. This is sent to the buyer's solicitor who will then ensure that the details are passed on to their client. You might also be inclined to provide your insurer's details so that the buyer can check out the possible insurance policies if they were to go ahead with the purchase.

If you are concerned about the legal side of buying or selling a property with a previous or existing subsidence problem, then why not talk to our team of experts who will guide you through the conveyancing process.

The experts at Homeward Legal are well-versed in all aspects of the conveyancing process, providing a quality service at a fee that is great value for money!

Call  to get your conveyancing quote started, or to discuss your concerns with your plans to purchase or sell your next home.