The common causes of subsidence and how to avoid it
The mere mention of subsidence is something that strikes fear into the hearts of many homeowners. It can cause major structural issues and does take time and money to fix. But what is subsidence, what are the causes of subsidence and is there anything we can do to stop it occurring?
What is subsidence?
Subsidence is when the ground underneath your home sinks or shifts. This movement causes disruption to the foundations, making the structure of your home unstable. Typically, you’ll notice issues such as a sloping floor, cracking along the walls and difficulty opening and closing your doors and windows. If you have an extension, you may notice it pull away from the rest of your home.
Common causes of subsidence
There are quite a few reasons why subsidence might occur. It can be due to a long-term issue or something more recent, such as changes in the weather or local flooding.
Some long-term problems may go unnoticed for many years, so they can come as a surprise to homeowners. However, if you live in an area with a history of mining, subsidence can be a common issue, even if houses have been standing for decades. Old mine shafts, tunnels and hollows can sit deep beneath homes and cause no problems. But over time, these can collapse – say, if an old mineshaft support crumbles – causing the ground to sink significantly.
Insufficient or poor foundations are another issue that can lie undetected for years. Some older homes will have been built before modern building regulations were introduced and therefore may not go as deep. This may not be a problem but changes to soil conditions – such as it drying out and shrinking – can lead to movement that the foundations simply can’t handle.
Tree roots can also be one of the causes of subsidence. They may contribute to drying out the soil, cause movement under the ground, or interfere with the drains. Collapsed drains also cause movement and the release of water underneath the house can rinse away soil, causing further damage.
Practical prevention
When buying a house, it’s important to get surveys done first, to make sure there are no known problems in the area – such as an old mine shaft under the house.
To protect the house you’re already living in, there are some sensible things you can do to prevent subsidence from happening. For instance, when you have an extension built, make sure it’s done properly by experienced builders as a poorly built structure is more susceptible to structural issues – not just subsidence.
Good home maintenance is also important. Looking after your drains by not putting items down there that might cause blockages and quickly resolving issues when they arise, will help to prevent cracking. Not planting trees too close to the house will also help to protect your drains and your foundations. Finally, consider making your home more resistant to flooding by reducing non-permeable surfaces outside and adding soakaways.
How to get subsidence repaired
How subsidence is repaired, depends somewhat on the cause. But in most cases, repairing subsidence isn’t as complex as you might think. That said, it will take skilled trades to sort it out. So, it’s not something you can do yourself.
The first step is to get a survey completed, so you can work out the cause and extent of the problem. This will help determine the best method for fixing the issue and how much it will cost.
Traditionally, the only way to fix subsidence was by excavating around the foundations and bolstering them with concrete and support bars. This method, known as underpinning, is still sometimes the best route to go down. For those properties that need extra support, mini-piling may also be required. This is where small, structural columns are dug into the ground to help provide extra stability. A newer, much easier method is resin injection. Here, a chemical formula is injected into the sunken ground beneath your home, raising it and stabilising it.
Of course, that’s not the only repair work that may be needed. There might be a drain line to fix along with cracks in the brickwork. Inside, there may be walls that need replastering and there may be doors and windows to refit.
The good thing about getting subsidence repaired is that it will ensure your home is structurally sound and will prevent it from losing value. In fact, homes with subsidence tend to be sold off cheaply, which is great if you want to buy a bargain. But if you’re selling, it’s much more financially savvy to get subsidence repaired before putting your home on the market. Not only should you see a return on the repair costs but it will open your home up to a much wider range of buyers.