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What Is Subsidence & What Causes Subsidence?
Subsidence is the gradual downward movement of the ground beneath a building, causing the foundations of the building to become unstable and the property begins to sink down as a result. Subsidence affects tens of thousands of UK residents every year, devaluing their property and compromising its structural safety.
Subsidence occurs for a variety of reasons, these can be:
Soil type / clay shrinkage
The foundation ground that your property is built on can have a major influence on the likelihood of subsidence. Properties built on clay ground are more likely to suffer from subsidence due to clay soil’s ability to hold water. In the warmer months this water, which is being held by the soil, can evaporate causing the clay to shrink, thereby pulling your property down.
A very common cause of subsidence is tree roots. Some trees such as oak, willow, sycamore, ash, and poplar are more prone to causing subsidence than others. Tree roots cause subsidence by absorbing the water from the soil under the footings. Just like in the warmer months, the soil then shrinks, which results in your property subsiding.
Washing away of soil / leaking drains
Any source of running water (leaking drains, flooding, heavy rainfall, etc…) can wash away and alter the soil underneath your property. This cause is particularly common for sandy and gravelly soil. Over time this causes the ground to shift and become less stable, eventually resulting in it giving way and subsiding.
Historic mining sites
Properties that have been built on historic mining or quarry sites are also at a higher risk of subsidence than other areas. This is due to the ground that it is built on being weaker and more unstable, as the material used to fill the site can shift as it decomposes. Reports can be purchased from the Coal Authority to see if your property might be affected.
There are several signs of subsidence that we recommend you look out for. As you can’t see what’s happening in the ground below your house, these signs are your best way to identify potential issues.
The most common sign of subsidence is cracks appearing in internal and external walls. Cracks are a mechanism for releasing stress in a structure, which naturally weakens your property’s design.
It’s important to note that not all cracks mean that your house is suffering from subsidence, small cracks are often just cosmetic and could purely be down to the age of the property. When assessing the cracks in your walls, it’s important to look at the following:
- Are two sides of the wall at differing heights?
- Is the crack wider than 5mm, or can you insert your little finger?
- Does the crack follow a zig zag or stepped pattern?
If you have cracks in your walls and answered yes to any of the above, then you may have subsidence. We’ve also created a handy crack gauge that you can download for free at home to measure and monitor wall cracks around your home.
Subsidence cracks commonly appear near doors and windows, as these are weaker points in the structure of the home and therefore more prone to cracking. The cracks can affect doors and windows differently depending on where they appear. Some may cause gaps to appear around their frames and for the door or window to swing open by itself, whereas some may cause the doors and windows to become stuck, jammed and difficult to open / close.
Sinking floors are often the most obvious signs of subsidence, but it’s still important to keep your eye out as it’s best to catch it as early as possible!
Sinking floors can form in different ways, if the subsidence is concentrated in the middle of the property, then the centre of the floor can indent or “dish”. Here you should look for the floorboards pulling away from the skirting boards primarily in the middle of the wall.
Sinking floors can also happen on one side or corner of the property, caused by the ground sloping a certain way. Again, the best way to visibly notice this is to see the floor pulling away from the skirting boards at a specific side or corner of the room.
Typical signs of subsidence before and after Mainmark's bespoke resin injection treatment:
Generally, subsidence is not an overnight occurrence, it can take many years for it to show any effects on your property. Because of this, the visible signs that do arise at the start are usually small and so some property owners may believe it’s something that can be addressed later. Unfortunately, this is never the best option. Subsidence is best dealt with as early as possible to minimise the work that must be carried out during the repairs.
Ignoring subsidence can have a wide variety of knock-on effects depending on what you use your property for. Landlords may struggle to rent out a property that has subsidence, as tenants want to feel secure in the home that they live in. People looking to sell their house will struggle to sell a house that has subsidence for the same reasons.
If you’re looking to continue living in the property, subsidence can also cause serious structural damage in the long term, and in the worst cases, can cause complete collapse of the property.
Historically, one of the few options for fixing subsidence was concrete underpinning. This was a costly, timely and messy procedure that included excavating the ground beneath your property and supporting the foundations with large volumes of concrete. Anyone living in the property at the time would have to move out, which could put families without a home for an extended amount of time, or a landlord without rental income.
Luckily, modern technology enables us to fix subsidence much more efficiently and much more cost effectively. Modern resin injection methods can be used to successfully strengthen the ground and re-level and repair homes affected by subsidence in significantly less time than it takes for traditional concrete underpinning. In the majority of cases, the occupants don’t need to move out!
Mainmark’s proprietary Teretek® resin injection solution is a proven, cost-effective and quick alternative to more invasive methods. Using a process similar to keyhole surgery, the work can often be completed in one day. It is widely used to strengthen foundation ground, re-level buildings and remediate issues in residential, commercial, industrial, mining and infrastructure projects.
When looking at what the cost of subsidence repair is, it’s important to note that every property is different. Factors such as what soil type and foundation ground lies beneath your property, what caused your subsidence and how serious your subsidence is all affect the cost of repair.
According to a Checkatrade report, the average cost to fix subsidence in the UK is £12,500. This takes in to account a range of different methods of repair, including the more expensive traditional concrete underpinning.
If your home if effected by subsidence, it’s important to check your home insurance policy before proceeding any further, as some policies will cover subsidence repair costs. However, if covered, the insurer will want to approve the method of repair that you are using and there will usually be an excess to pay.
It’s also important to look at subsidence repair as a long-term fix. Ignoring subsidence and leaving it to get worse will only raise the price of the repair in the future. On top of this, if you ignore subsidence and the worst does happen – property collapse – then the cost of repairing and rebuilding will far outweigh anything you’d have to pay now.
For many, purchasing a property is the biggest investment of their life. The buyer and the seller will want a smooth process, however, there will often be a need for compromise.
For sellers, the final sale price is typically the biggest compromise, while buyers usually need to be flexible regarding the location, layout and size. However, expensive structural repairs may be a deal breaker for many house hunters.
If you’re buying a house and you suspect that it has subsidence, then you should have a full building survey done, this should inform you if there is any risk of subsidence. If subsidence repair work has taken place in the past, then you should obtain documents from the seller to verify that repairs were done to the standard set out by the Building Research Establishment. These documents should include:
- A formal completion certificate (issued by the council).
- A certificate of structural adequacy.
There may be some guarantees within these repair documents that you will want passed on to you. It’s also a good idea to find out more about the insurance for the property, as properties with a history of subsidence may have limited or more expensive policies.
If you’re selling a house that has subsidence or has a history of subsidence, transparency is key. You may also have to be prepared to lower your asking price; a 2021 report by SOLD.co.uk found that houses affected by subsidence saw a valuation decrease of 20% – 25%.
Sellers should remember that having subsidence on a property does not mean that it can never be sold! Your property will have many positives that you should look to promote and if the work has been completed to the appropriate standard, it is only a matter of time until a buyer is found.
So you’ve identified the issue, completed the work and your property is now free from subsidence. The next question you may have is how does this affect the property going forward?
Well, at renewal you will need to be prepared for the fact that there may be a smaller number of insurers who will insure your property and that the premiums will more than likely be higher.
Your existing insurer will normally continue to cover you, or you can contact BIBA (The British Insurance Brokers’ Association) for a specialist broker. You should look for an insurer who will ‘transfer’ the insurance to a new buyer. This will make any future house sale much easier as it alleviates one of the issues a potential buyer may face.