What is subsidence? Our Ultimate Guide
Subsidence is the sinking of the soil underneath a property, leading to structural movement of the building. The most obvious signs of subsidence are cracks in the internal and external walls. Subsidence can have a significant impact on property insurance premiums and the value of a property, but there are different types of subsidence.
What is subsidence and what’s the difference between historic movement and active movement?
Subsidence happens when the ground loses moisture and contracts. This could be due to environmental or man-made factors. Ground sinking will cause the foundations of a property to move and affect its structural integrity.
Historic Movement
If a property has experienced ground sinking in the past, but this has stopped or been fixed, this is called ‘historic movement’. Many properties are affected by historic movement. Houses will often move a little in the years immediately after they are built, as their foundations settle. It does not mean that the property cannot be insured and is less of a problem than active movement.
Active Movement
‘Active movement’ is the more serious subsidence issue. This is when subsidence is currently taking place. Insurers will be more wary of a property where a surveyor has reported active movement.
What are other issues often mistaken for subsidence?
There are several other geological processes that cause buildings to move, but they should not be confused with subsidence. They have different impacts on properties and are regarded as distinct issues by insurers. ‘Heave’ is when the ground moves upwards as a result of soil expanding; ‘Landslip’ is the downward movement of sloping ground, and ‘Settlement’ refers to soil that compacts or compresses under the weight of a building within 10 years of its construction.
What causes subsidence?
Environmental factors are the most common causes of movement underneath buildings. Soil that loses moisture is the No.1 cause of subsidence in the UK, and it is no coincidence that there are more instances of subsidence in the south east of the country than anywhere else, which is also the driest part of the UK. As climate change is only going to make periods of drought more frequent, instances of subsidence are predicted to increase.
Subsidence is also more likely to occur in clay soils – clay reacts in a more volatile way to changes in weather. Clay dries out, cracks and shrinks in hot weather, and expands when wet. Tree root activity is also a major cause of subsidence. If the roots of old trees are allowed to grow freely they can creep into the foundations of buildings, taking water from the soil.
Too much moisture in the soil is also a problem. Heavy rainfall and high groundwater levels can wash away earth and unsettle a building’s foundations.
Other long term causes can be geological processes such as seismic and volcanic activity and sedimentary compaction, but these are most commonly found in other parts of the world.
What are the property related and man-made causes of subsidence?
The most common cause of subsidence from human activity is leakage from mains water pipes, drains, gutters and underground utilities. Leaks can soften or wash away the soil under foundations. The age of the building plays a part too. Victorian and Edwardian properties were more often built on shallower foundations than today, and are more likely to have experienced movement in the past. If a building has been extended or seen more recent development, this could cause problems. Modern building regulations call for deeper foundations but more rigid materials, so different parts of a building could move at different speeds.
Historic mining activities may also lead to subsidence. Even if the pit or quarry has been filled in, this material can shift over time and cause ground sinkage.
What are signs of subsidence you should look for when buying a property?
Cracks
Cracks in walls are the tell-tale sign of subsidence, but not every crack in a house means it is sinking. Most houses develop cracks, and they can be entirely innocent. They just mean that stone, brick, plaster and other building materials are shrinking or expanding naturally with the seasons and changing temperatures.
What does the crack look like? If it is wider than 3mm, diagonal in shape, and appears close to a window or doorway, then it could be a sign of subsidence. Hairline cracks in external brickwork are quite common. Large cracks in brickwork are a greater cause for concern, especially if they are wider at the top of the building.
Uneven floors, sticking doors and windows
If floors are uneven, or doors and windows are sticking and not able to be opened or closed easily, it may mean they are being warped by the movement of the building. Similarly, you should be concerned if gaps in the brickwork start to appear around doors and windows.
Other signs of subsidence
What are the other things to look out for if you think your house is suffering subsidence? Inside, you might find rippling wallpaper and peeling paint, bulging walls or bowed ceilings, or a visible tilt or lean in a room. Outside, the presence of sinkholes or depressions, cracks in driveways or pathways may be signs of subsidence.
How do surveyors check for subsidence?
If you think your house is subsiding, the best thing to do is arrange for a subsidence survey. This type of survey is conducted by a qualified structural engineer who will know what to inspect and look out for, and recommend remedial actions. As a buyer, a structural survey will usually identify signs of historic and active movement, so that you know the risk before you buy.
How much does subsidence devalue a property?
If a structural survey reveals active movement, it does not mean that the house is unsellable or uninsurable. It will significantly affect the valuation, and a process called underpinning will be required to make the property stable. On average this devalues a property by 20-25%, even after the underpinning work has taken place.
Is it hard to sell a house with subsidence?
Yes, but not impossible. Sellers will have to reduce the asking price significantly, and declare that the property has been underpinned. This is a legal requirement. The pool of potential buyers will in all likelihood be limited to cash buyers, because mortgages are very difficult to find for a property with active subsidence.
How to fix subsidence
As we have said, underpinning is the main structural work required for the most serious cases of subsidence. There are three forms of underpinning – piling, for very deep foundations; beam and base; and mass concrete. Surveyors will be able to say which is the most appropriate type of underpinning for your property or the property you are interested in buying.
Underpinning is the last resort to fix subsidence, but property owners can reduce the risk of subsidence with some ongoing maintenance. Get professional help to prevent exponential tree root growth, repair leaking pipes, fill cracks in walls and secure gaps around doors and windows. Monitor soil moisture levels around the property to prevent excessive drying or flooding, ask a surveyor to inspect the property’s foundations regularly, and schedule periodic structural surveys. It will be expensive but subsidence is one of the costliest things to go wrong in a property.
How does subsidence impact buildings insurance?
Subsidence is an issue that insurance providers take very seriously.
There is no time limit on declaring incidents of subsidence to insurance companies. Even if the movement was historic, it must still be declared every time you renew a policy or change insurance provider. Premiums will be higher, but some insurance companies will still provide cover if preventative works to stop the subsidence have been successful.
Standard buildings insurance policies include subsidence cover, as long as there is no known active movement for the property. The excess on subsidence claims will be high, usually at least £1,000. If you make a claim for subsidence works, your insurance provider will usually exclude subsidence cover from any renewals. Subsidence cover only includes the cost of repairs for a subsidence event, rather than the cost of preventing further subsidence in the future. Check what is included and excluded in the subsidence policy terms.
Let us help with your property search
If you are thinking of buying a property, we can help with all aspects of the buying process, including any concerns you may have about subsidence. Simply get in touch with your local haart branch.