Subsidence

What is subsidence?

Subsidence is among the top worries of homeowners and buyers. Aside from increased risk from structural disasters, subsidence may bring expensive repair bills that everyone wants to avoid.

In this article, we are going to look at the issue in detail as we discuss its signs, ways to avoid and deal with it, as well as its implications on a property’s safety and value.

What happens when there is subsidence?

In simple terms, subsidence is the sinking of the ground underneath your property due to instability of soil. When there is subsidence, the foundations of a house, or any property, become misaligned, which eventually poses a structural threat. It can occur to any property; however, subsidence is mainly a problem in certain areas with certain soil types.

When applying for property insurance, most homeowners frequently confuse subsidence with heave and settlement, which are phenomena also caused by ground movement.

Unlike subsidence, heave is a case where the ground underneath a property moves upwards, causing foundations to be pushed upwards. Settlement, on the other hand, is also a downward movement of the ground your property sits on; however, it is caused by the compression that the soil is experiencing from the weight of the property (usually 10 years after the property was built).

It is worth noting that settlement is not covered by most property insurance while subsidence and heave are covered if considered reasonable. To avoid expensive bills, you have to check with your insurance provider as soon as you have suspicions of subsidence in your property.

What causes subsidence?

Although subsidence can happen anywhere, houses and properties situated on specific areas are most at risk of subsidence. These include properties in areas where soil types like clay, silt, sand and gravel are more dominant. Some of the main hotspots of subsidence in the UK are big cities like London, Birmingham and Manchester.

Aside from the nature of soil or soil type, there are also a number of reasons why subsidence occurs:

• Man-made vibrations of the ground (construction, railway, road works, etc)
• Mining activity on the area
• Nearby vegetation that takes out water from the soil
• Leaking drains and pipes
• Large trees and shrubs planted near the property
• Drying out of soil / drought
• Other natural disasters like earthquakes and flood

Contributing factors mentioned above can higher the risk of your property to experience subsidence. For prospective homebuyers, it is important to know what surrounds the property you are interested in to avoid unexpected problems like subsidence. Checking out subsidence maps can also help you identify areas where there is high probability for subsidence to occur. Areas that experience flooding often are also at risk.

What are the signs of subsidence?

A crack in a wall does not necessarily mean that subsidence is occurring in your property. Most houses suffer cracking and sometimes, cracks appear because of the swelling of walls and floors as temperature changes. Cracking is normal occurrence in buildings; however, it is also the most common sign of subsidence.

The first sign of subsidence are cracks, particularly diagonal cracks, in the ceilings and walls around doors and windows. Cracks caused by subsidence are at least 1mm – 3mm long and are wider at the top than the bottom. Existing cracks also expand when there is subsidence.

Aside from cracks, wall and ceiling rippling in wallpapered rooms as well as sticking of doors and windows are also signs of subsidence. Be vigilant of these signs to address subsidence as early as possible.

If you are unsure whether there’s subsidence in your property, must get in touch with a chartered surveyor to carry out an assessment. Once an assessment has been conducted, you may also contact your insurance provider in order for them to send a loss adjuster to estimate the potential cost. From this, your insurance provider may advise you the best action to take and even recommend you to a trusted contractor.

What should you do if there is subsidence?

Resolving subsidence is a case-to-case basis. There is actually no exact way to treat it, but the most effective way is to identify the root cause – you must first identify what caused the soil underneath your property to be unstable. Once known, the issue must be addressed immediately.

If there are leaking drains and pipes, you must fix these instantly as to not worsen the situation.

There are some cases where large trees and shrubs around the house or property are causing the ground movement. In this case, a tree surgeon must be consulted to remove the tree. Removing the tree on your own or without the help of professionals might worsen the situation so be careful.

It may take a while before subsidence can be confirmed. A lot of observation and monitoring may be needed in order to identify the root cause and to ensure that all problems causing the ground movement are addressed.

If none of the immediate solutions work, the property may need to go underpinning which is recommended as the last resort to deal with subsidence.

What is underpinning and when do you need it?

Underpinning is a construction method to repair and prohibit further movement of the foundations of properties experiencing a severe case of subsidence. This procedure works  by excavating the ground to either replace foundations with new materials or to repair existing ones. During underpinning, the depth of existing foundations are increased to transfer the building weight to a more stable soil type. There are different types of underpinning but for subsidence, mass concrete underpinning or the pit method is commonly used.

Not all properties experiencing subsidence need to undergo underpinning. To know whether a property needs underpinning, a building or structural survey must be conducted by a chartered surveyor. Severe signs of subsidence include a huge hole appearing in the ground or if the property seems to lean on one side. Once advised by a surveyor to undergo underpinning, the property owner must seek professional services as this method is very sensitive and may cause serious damage or even make the property collapse if not done right.

Underpinning is a costly procedure which ranges around £15,000. The severe the case of subsidence, the higher the cost would probably get. Its cost will also depend on the size and extent of the work.

Always remember that underpinning must only be carried out by a specialist with the help of ground works contractor. Certain requirements of the Party Wall Act 1996 must be followed by owners of properties in close proximity with another property. This act serves as guidelines and framework to avoid disputes with regards to boundary walls and excavations in neighbouring buildings.

How do you avoid subsidence?

Although not all cases of subsidence can be prevented, owners of properties that are at risk can still perform a couple of ways to prevent this phenomenon from happening.

Some of these ways are:

• Keep drains and pipes well-maintained so as to avoid water leakage. Blocked or leaking drains should be repaired immediately. Water from leaks make the soil unstable. Sources of excess water should also be avoided. This can be done by using water butts, rain barrels and tanks to collect rainfall.
• Ensure that large trees and shrubs are at a safe distance (not too near the property). It is advisable to plant any kind of tree at least 10 metres and keep large trees at least 40 metres from the property.
• Perform pruning regularly to control the height of trees and shrubs, thus, reducing the amount of water they absorb.
• Do not remove trees on your own. Digging up in the wrong parts of the ground may higher the risk of subsidence. Always consult with a tree surgeon for advice.
• Be mindful of what type of trees you plant around your property. The Association of British Insurers (ABI) has prepared a guide on safe distances of trees, depending on species, from the property.

Should you buy a property that has been underpinned?

It is important for prospective homebuyers and property investors to know whether their properties of interest have experience subsidence and have undergone underpinning as this issue affects the value of the property.

Basically, a property that has been underpinned do not usually get insured as they are seen to be structurally weak. However, there are still insurance providers that cover underpinned properties.

Once you have decided to buy an underpinned property, you should seek a chartered surveyor for a full structural survey to know other issues that might affect your property. In addition, an insurance provider must be contacted as soon as the property becomes your responsibility.

Written by Heidecel Serrano