In a nutshell, underpinning is a method used to rectify properties that have suffered from considerable subsidence. This technique is used to provide support to the structure of a property, to ensure that it remains structurally sound. As a property owner, you may be wondering, when is underpinning required and what are the signs of subsidence?
There is a range of causes for subsidence and several reasons why you may need to underpin your property. In this article, we’ll provide our in-depth guide for underpinning along with what you should be aware of if purchasing an underpinned property.
Four Main Reasons Why Properties Require Underpinning
- The property has aged, and as such, the foundations are no longer strong enough to support the foundation of the property. Wooden supports may have eroded over time or footings may have weakened. This requires reconstructive work to provide stability to the property
- Extensions, the addition of extra floors or changes to the existing property can alter the stability of existing foundations. This is because the use of the previous structure has changed and it may not be able to accommodate for the additional strain. The property, therefore, requires strengthening to account for the additional structure and weight.
- The structure of the soil underneath the property has changed. This can affect the stability of the foundations of the property and weaken its strength. This change may have occurred due to trees soaking up the water, leaking drains softening the ground or excessive weather conditions that have altered the condition of the ground. Whatever the reason, subsidence may have occurred, leading to a cavity that the property will sink into.
- A natural disaster such as flooding, drought or an earthquake may have caused the structure to move. This may have damaged or altered the structural stability of your property.
What is the Purpose of Underpinning?
Underpinning is performed to reinforce the structure of the property. Any of the aforementioned reasons may have been the culprit of change, however, all causes require remedial attention. The extent of the damage can vary between each, altering the amount of reconstruction required. The most commonly occurring need for underpinning tends to be due to subsidence. This is when the soil under the property shifts and the property begins to sink into a cavity.
In cases such as these, the existing soil and structure will be excavated to make room for replacement materials. This soil will be replaced with deeper footings, strengthened foundations and new soil. This should provide the property with additional support, reinstating its previous structure. Overall, the process aims to provide a firmer ground for the foundations of the building and enhance its structure. If completed professionally, this action should prevent subsidence issues for several decades.
What is Subsidence?
Subsidence occurs when the soil underneath a property shift and causes the property to sink. This movement of soil reduces support to the existing structure of the property, as well as its foundations. There are several causes of subsidence that will likely require underpinning to remedy them. They include:
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Weather Conditions
Consistent alterations to the soil from weather conditions can detrimentally affect the security of your property. Fluctuations such as long periods of consistently wet weather followed by long periods of dry summers are known to create unstable structures. This is due to the way that soil behaves under various conditions. When soil is wet it expands, whereas when it is dry for extended periods of time, it contracts.
Properties constructed in areas that are prone to droughts can frequently suffer from subsidence issues. During the heat, the soil may shrink, dry out and crack. Whereas long periods of wet weather will cause the soil to move drastically, often resulting in cavities for the property to sink into. Underpinning is certainly required to offer additional support.
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Tree Roots
Perhaps less severe than extreme weather changes, subsidence can also be caused by factors such as tree roots. In a similar manner to the hot weather previously mentioned, tree roots absorb the water from the soil underneath your home. This removes the moisture from beneath your home, destabilising its structure. After long periods of dryness, downpours of rain can cause severe shifting of the soil, causing major structural issues.
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Mining
Whilst less common, the repercussion of mining or excavation work can be a clear cause of subsidence. This is due to the gap in the support and structure of the property with the space below ground level. The building supports face more strains and can be weakened due to the suspension of the ground. Over time, a property and its structure may give way to sinking into this gap if not reinforced properly.
How to Spot Signs of Subsidence
If you are considering purchasing a property, or are the owner of a property and are concerned that there may be existing subsidence issues, there are actions you can take. As new owners or potential buyers of a property with subsidence, the most important thing to do is to instruct a certified RICS surveyor to assess the structural strength of your property. They can identify several issues associated with the condition of your property. This may include, issues with subsidence as well as further structural problems associated with the building. They will also be able to identify whether remedial work is required and advise you on the best strategy for underpinning.
If you’ve been residing in a property for several years, you might be concerned that your property is developing issues with subsidence. Before taking immediate action, there are certain things you can look out for. This includes:
Cracks within any of the following areas:
- Interior or exterior brickwork
- Within extension joints
- Cracks that are 3mm wide
- Close to windows and doors
- Cracks that are wider at the top than the bottom
- Found after periods of dry weather
Other symptoms such as wrinkling wallpaper and jammed doors and windows may also be signs of subsidence.
If any of these signs are present in your home, it is important to request the services of a surveyor. It is important to address the severity of this issue before your property becomes unstable and dangerous.
Final Thoughts
Soil subsidence can be caused by a number of factors, but the most common causes are extreme weather conditions and tree roots. If you’re considering purchasing or living in a property that has already suffered from soil subsidence, it’s important to have an expert surveyor assess the structural stability of your property. You’ll also want to watch for signs like cracks in interior or exterior brickwork as well as extension joints; if any of these symptoms are present then make sure you call on the services of a specialist RICS surveyor as soon as possible!