Are you considering buying a house with subsidence?
If you have discovered that a house you are interested in has history of subsidence, you are likely to have a number of questions.
What exactly is subsidence? What causes subsidence? What impact could subsidence have on any future sale? What are the risks associated with buying a house with subsidence?
What is subsidence?
Subsidence is the downward movement, or collapse, of the ground that a property sits on.
All properties will experience a small amount of movement, which will largely go unnoticed. However, when the movement occurs in a downwards direction, and causes the property to become unstable, it is important to take action to protect the property from extensive damage.
What is the difference between subsidence and settlement?
Most newly-built properties will experience some degree of settlement. Settlement is caused by the ground beneath a property compacting under the weight of the new structure.
Unlike settlement, subsidence is not caused by the weight of the building. Subsidence is caused by the ground beneath the property becoming unstable, and would have occurred whether there was a property built on the land or not.
The opposite of subsidence is ‘heave’. Heave becomes apparent when the ground beneath the property swells and moves in an upwards motion.
Signs of subsidence
The most obvious sign of subsidence is the appearance of subsidence cracks in walls. When the ground beneath your property becomes unstable, and moves in a downwards motion, it will take some of your property’s foundations with it. As one section of your property begins to sink, it will put pressure on the structure of your home, and cracks will begin to show at the point of tension.
Subsidence warning signs
Several factors may put a property at a greater risk of subsidence. These include:
Trees that cause subsidence
Large trees, close to your home, can cause problems with the stability of the property’s foundations. Large tree roots can disturb the soil beneath the foundations, and thirsty plants may dry out the ground, leaving it more vulnerable to cracking and movement.
The property’s foundations
Older properties generally have shallower foundations, which may leave them more susceptible to erosion and subsidence.
Clay soil is particularly prone to cracking, shrinking and moving during warmer, drier weather. This can unsettle the property’s foundations and cause subsidence. A good way to assess whether clay soil is likely to cause a problem is to look closely at the surrounding properties. Can you see any external cracks?
Any damaged water mains, or household drains, can create an added subsidence risk over time. Soil that becomes saturated with water can easily become unstable and erode under the weight of a property.
Nearby mining history
Any area that has a history of mining has an increased risk of experiencing subsidence. It is important to gather information about any historic mining activity as part of your pre-purchase property searches so that you can take the necessary steps if the property is at risk.
Are cracks always a sign of subsidence?
No, they are not. Signs of settlement and weather changes can easily be confused with early signs of subsidence, which is why it is important to have any cracks thoroughly investigated by a qualified, chartered surveyor.
Small hairline cracks, which appear seasonally, are likely to be due to the expansion or contraction of materials in changing weather.
Cracks that are a result of subsidence will usually be larger (thicker than 2mm) and more visible (it is likely you would be able to see them both internally and externally). You would also expect the cracks to be wider at one end, and often diagonal in direction.
Another early sign of subsidence may be that your doors and windows start to stick, as they become misaligned.
How common is buying a house with subsidence?
It is estimated that subsidence affects around 40,000 properties each year. How common house subsidence is in your area will depend on your location.
In former mining communities, such as East London, South Wales and the North East of England, subsidence can be very common. Similarly, homes built in areas with clay soil will be more vulnerable to movement and erosion. Insurers will be aware of these areas of increased risk, and insurance premiums in the area will generally be higher as a result.
Underpinning a house
Underpinning is the process of strengthening the foundations of a property that has been affected by subsidence.
There are several different techniques used to underpin a property, depending on the level of damage and the original cause of the subsidence.
Mass concrete underpinning
Mass concrete underpinning is a way of extending, or deepening, existing foundations, and is the most common method of property underpinning. During the process, areas of ground beneath the existing foundations are excavated and then filled with concrete. This process is completed in small, manageable sections to ensure the property remains well supported during the underpinning work.
Piling is seen as the most versatile method of strengthening a property’s foundations. Piles are driven into the ground, bypassing the weaker, looser soil, to sit on more stable soil or bedrock below.
Jet grouting can be used to strengthen weak soil beneath the existing property foundations. High-pressure jets are used to mix existing soil with a self-hardening grout, creating a strong, substantial base to support the property’s foundations.
How much does underpinning cost?
How much it costs to underpin a property will depend on the severity of the problem, along with other factors such as the location and accessibility of your property.
Buying a house with structural movement
Before you consider buying a house with subsidence, you should ask three key questions:
- What was the original cause of the subsidence and is it likely to cause future problems? (ie. has the root cause been addressed?)
- Can the current owner’s buildings insurance policy (which will include subsidence insurance) be transferred to you, and would you be entitled to make further subsidence claims against the policy?
- Would your mortgage provider be willing to lend against a property that has previously had subsidence issues?
Will subsidence devalue my house?
Your property is only worth the figure someone is willing to pay for it. Any potential buyer is likely to face significantly more expensive buildings insurance premiums, and as a result may well feel it is right that this future financial commitment be reflected in the property purchase price.
Some potential buyers will be put off buying a house with subsidence, or history of subsidence, meaning your target market may also be reduced. This is likely to have an impact on the level of offer you can command.
Selling a house with subsidence history
If you are planning on selling a house that has been underpinned, it is important that you have the necessary information in place before any viewings. If the cause of the subsidence has been addressed, and the problem has been resolved, you will need to supply a Certificate of Structural Adequacy. A Certificate of Structural Adequacy will detail the cause of the subsidence, the extent of the damage, the work carried out to address the problem, and a statement confirming that the property is now structurally sound.
If your property is currently showing signs of subsidence, you may find that potential buyers are unable to secure a mortgage to purchase the property. When this happens, you may need to consider selling to a cash buyer who is happy to take on the property in its current condition.
In order to reduce the risk of your property sale falling through as a result of subsidence problems, it is important that you are honest and open about the property from the start. If your would-be buyer does not find out about any previous (or current) subsidence until they have a survey done, they will wonder what other problems they might have to deal with, and are likely to feel cautious about proceeding with the purchase.
Should I buy a house with subsidence?
There is no denying that subsidence is a serious issue for a property, but does that mean you should be put off buying a house with subsidence?
If you are considering buying a house with subsidence, you should have a comprehensive structural survey carried out to ensure that any problems have been fully rectified.
Any house that has been underpinned is likely to be more expensive to insure, so it is a good idea to get a buildings insurance quote before you decide to pursue buying a house with subsidence.
It is also worth thinking about how the property’s history of subsidence will affect the value of your home, and how easy you may find it to secure a buyer when you come to sell the property.
Pictures of subsidence in a house
These are some of the most common signs of subsidence in a property:
Diagonal subsidence crack in external wall, near window.
Diagonal subsidence crack, wider at one end.
Cracks in garden or driveway paving can also be a sign of subsidence.
Large subsidence crack in an internal wall.
Cracks low down on an exterior wall can show that the property has become unstable.