Your Guide to Subsidence and Underpinning
This article looks at what subsidence is, gives tips on how to spot it and your options for getting it fixed and how to avoid it in the first place. We also look at any implications for a future sale, and if purchasers should walk away from the deal.
What is subsidence?
Subsidence happens when the ground your home is built upon sinks. As the ground beneath the property falls in, the foundations of the house become misaligned, which can be particularly problematic when the ground sinks at different rates.
It is important to note the distinction between subsidence and “settlement” because most insurers do not cover settlement. Subsidence, according to the Financial Ombudsman Service, is caused by the: “downward movement of the site on which a building stands… where the soil beneath the building’s foundations is unstable”. But settlement is “downward movement as a result of the soil compressed by the weight of the building within ten years of construction”.
What are the signs of subsidence?
Be reassured, the presence of a solitary crack in the wall does not mean your property has subsidence. It is far more likely to be caused by walls or ceilings swelling and shrinking because of changes in temperature over time. Also, a new build property, or one that has had major re-plastering work, is likely to develop small cracks as the plaster dries out or the structure settles onto its foundations.
A crack caused by subsidence will probably be:
- Wider than 3mm (the width of a 10p coin)
- Visible on both the inside and outside of the property
- Diagonal and typically wider at the top than the bottom
- Located close to a window or a door
Cracks are not the only sign of subsidence. You should also look out for windows and doors that stick because this could be caused by subsidence warping the frames as the house sinks. Wallpapered rooms may look “rippled” at the wall and ceiling joints and, if you have an extension, you may also notice cracks where it has been joined to the main part of the house.
I have suspicious cracks, what should I do?
If you have a real concern the cracks are down to subsidence, you should contact your buildings insurer, because as soon as it is spotted the easier it will be to deal with. Your insurer will arrange for a surveyor to come and inspect the building and confirm the presence of subsidence. If there is any doubt, the surveyor may decide that the home needs to be monitored for a period of time to allow them to determine whether the ground is, in fact, sinking. This can sometimes take up to 12 months.
The downside to telling your insurer straightaway is that it may mean your insurance premiums rise, even if it turns out there was never any subsidence present. However, you should keep in mind that all insurers views risks differently, and the disclosure may not make any difference to your premiums at all.
What houses are most at risk of subsidence?
Some homes are at greater risk than others of subsidence, and this is usually because of a combination of factors. The main risks that increase the chances of sinkage are:
- Trees – It there are large trees or shrubs close to the building they may cause sinkage as the plant drains the moisture from the soil, causing it to dry out and sink. It has been found that approximately 70% of all subsidence cases result from tree roots absorbing the moisture from the soil.
- Clay – Because of this type of soil changing with the weather, there is a greater risk of the building sinking. This is because when the weather is hot and dry, it causes the soil to contract, crack, and shift, which makes the ground unstable.
- Drought – if the home is situated in an area prone to drought, this could cause the soil to dry out, which increases the risk of subsidence.
- Leaks – A leaking water main or drain can soften the soil, perhaps even washing it away, causing subsidence.
- Age and construction – If the home is a period property, it is more likely to be at risk of sinkage than a newer home. This is because older properties usually have shallower foundations. However, it is not all doom and gloom with period homes – as they tend to be built from bricks and lime mortar which make them more flexible and less likely to be damaged from the ground shifting beneath them, than more contemporary constructions.
- Mining – One of the better-known causes of subsidence. If the property has been close to a former quarry or pit, then it could shift as the material used to fill the site will move as it decomposes. Reports can be obtained from the Coal Authority if you think your home may be affected by a former pit.
There are steps you can take to reduce the chances of your property being the victim of subsidence, for example:
- Keep trees at a safe distance from your home and don’t plant any within 10 metres. Larger trees should be no closer than 40m. You can obtain a guide to planting trees within the boundaries of your home from The Association of British Insurers, which provides a run-down of popular domestic species, detailing how tall they are likely to grow, and safe planting distances.
- Try to catch excess water – use water butts to catch rainfall, keep guttering, pipes and plumbing well-maintained to avoid leaks. This will prevent the soil around your home from becoming waterlogged and will reduce the risk of sinkage.
If the subsidence is being caused by tree roots, then the easiest solution is to remove the tree. That said, this should only be done in consultation with your surveyor and with the help of a tree surgeon. You should also bear in mind, if your home is in a conservation area you will need to contact your local authority for permission to remove the tree. In addition, even if your home is not within such an area, a Tree Preservation Order (TPO) may have been registered. If so, you will need to apply to the council to have the TPO removed prior to felling the tree.
In the worst cases of subsidence, the house may need to be underpinned. This can be both expensive and disruptive, with costs running around the £50,000 plus mark. The Royal Institution of Chartered Surveyors (RICS) has estimated that approximately fewer than 10% of subsidence affected properties need underpinning.
Underpinning is a method of construction for properties suffering from current or historical subsidence. Typically, underpinning is required when the structure of a property moves so much that the foundations need to be repaired. Essentially, the soil beneath the existing foundations is excavated and then replaced with new materials to repair the property’s structure.
For any property that is structurally unsound and in need of underpinning, you will need to obtain professional help and advice. There are a variety of methods builders employ to underpin a property, but if it is not carried out properly and with the expertise it deserves, it can lead to serious damage or even structural collapse of the entire building.
Although underpinning can be expensive, if left unresolved, the cost is likely to spiral out of control and put your entire property at risk. The cost of underpinning is always worth it in the long run, for the sake of ensuring your property is structurally secure and safe to live in.
Buying a property with subsidence
Whenever you are viewing a property, you should always keep an eye open for evidence of subsidence. If you have any suspicions, ask the estate agent or seller directly whether the property has ever suffered from subsidence. If you suspect the property has been affected, it is advised you obtain a full buildings survey which will inform you of the risk.
If repairs for subsidence have ever been undertaken, your conveyancing solicitor should obtain legal documentation from the seller to confirm the repairs have been completed to a standard set by the Building Research Establishment. Documents should contain a formal Completion Certificate, which is issued by the local authority if the property has been underpinned, together with a Certificate of Structural Adequacy, which will have been filled in by a building surveyor if the repairs were part of an insurance claim. Many repairs also come with certain guarantees which you will want to make sure are passed on to you.