What are the signs of property subsidence and how to prevent it?
Recognising the signs of subsidence can help you to know if your property is simply settling or whether it has a more serious structural issue.
Our structural engineering experts explain the key signs that property subsidence is present and the actions you can take to prevent it from worsening.
What is subsidence?
According to the Association of British Insurers, subsidence is defined as ‘when the ground beneath a building sinks, pulling the property’s foundations down with it’.
However you define it, subsidence is a very serious issue; one that adversely affects the structural integrity and future safety of your home. When subsidence occurs, it means that the ground beneath your property is sinking. As a consequence, the foundations of your property become disturbed and collapse, at which point your home no longer has a solid foundation to give it strength and stability.
Is subsidence the same as settlement?
No, subsidence and settlement are not the same.
Settlement occurs in the time immediately following a building’s construction, and is caused by the soil beneath it adjusting to the weight of the new structure bearing down on it. Settlement, therefore, is a normal process, even though it can occur over several years.
Subsidence, on the other hand, affects a building after it has been standing for some time. It is not simply a case of the earth adjusting to the building but a sign that the foundation of your property has been compromised and needs immediate attention. Unlike with settlement, which is perfectly harmless, subsidence can cause serious damage to your home if left unchecked.
What causes subsidence?
There are several main causes of subsidence:
Soil type and trees
As highlighted in our Types of Foundation in Construction blog [INSERT LINK], clay soils are particularly vulnerable to property subsidence because they shrink and swell during different seasons. This is amplified where trees are present, as their roots remove water from the soil, destabilising the ground and drying it out.
Leaking drains
Leaking drains can wash away or even soften the founding substrate below your property, again leading to subsidence. Granular soils (like sand and gravels) are most vulnerable to washing away, whereas cohesive soils (such as clay) are most vulnerable to softening. During any investigation into subsidence, a CCTV of the existing drains is recommended.
Mining activity
Subsidence can also be caused by old mines, quarries, or pit sites that have been infilled. Should the infill material collapse, the ground directly above it becomes vulnerable to instability. As a consequence, any homes constructed over such sites are at increased risk of subsidence.
Weather/Climate
Extreme weather or climate change is also cause for concern when it comes to issues of subsidence. Similar to the way in which the presence of trees and drains can impact moisture content in soil, adverse wet or dry weather can also cause the ground beneath your home to become waterlogged or parched, either of which could disturb your property’s foundations.
What are the signs of subsidence?
Signs of subsidence include:
- cracks suddenly appearing in walls and ceilings after many years
- doors and windows that no longer close properly
- previously level floors becoming uneven
- a sudden widening or lengthening of cracks on walls, ceilings, or around doors and windows
If you notice any of these signs, it is important to act as soon as possible to minimise the risk of further damage to your property.
How can I prevent property subsidence?
If subsidence is already present in your home, or the signs of subsidence are appearing, you should contact a qualified structural engineer or building surveyor who can assess the extent of the damage and recommend appropriate remedial work.
At worst, your home may need to be underpinned. This course of action involves excavating the ground beneath the foundation of your property to reinforce it with concrete or steel. Another remedial measure available, particularly if the subsidence is detected early, is to inject grout or other stabilising materials into the soil, to prevent further subsidence of the property from occurring.
In summary: recognising and preventing subsidence
Property subsidence is a serious issue that can cause significant damage to your home if left unchecked or untreated. If you suspect that your property is experiencing subsidence, it is important to call in a professional (such as a structural engineer or building surveyor) as soon as possible to prevent the problem from worsening.
Regularly checking your drains, and avoiding planting trees too close to your property, are just two preventative steps you can take to hinder subsidence from occurring. If subsidence is already present at your property, only a qualified structural engineer or building surveyor can recommend and conduct the necessary remedial works to stabilise the building and prevent further damage.
Engineering differently for your project
Considering a new build or rebuild project? Talk to our accredited structural engineers about a build design that mitigates risk of subsidence. Contact the team here.
About
dbstructural are a team of value-led iSTRUCTE accredited structural engineers based in Leighton Buzzard, Buckinghamshire, covering the UK.
Our values are at the core of everything we do. Engineering differently to ensure a better future for our team, our clients, and the communities of the buildings we design.