- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 10 Apr 2018
Subsidence of buildings
Subsidence occurs when the soil beneath a building is unstable and sinks downward. This is not the same as ‘settlement’, which is caused by the weight of the building, but it can still have a negative impact in terms of the overall structural stability. The opposite effect of subsidence is ‘heave’, where the site upon which the building is situated moves upwards and/or sideways.
According to Subsidence Support, ‘Over the last 10 years the adverse effects of subsidence caused by shrink-swell behaviour of soil have cost the economy an estimated £3bn, making it the most damaging geohazard in Britain today.’
 Signs of subsidence
- Sudden appearance of cracks, especially after a prolonged period of dry weather.
- Vertical and diagonal cracking in specific areas, tapering in width between the top and bottom.
- External cracking which also occurs in the same area internally.
- Opening and closing of cracks on a seasonal basis.
- Cracking occurring around weak structural points, such as doors and windows.
 Causes of subsidence
Subsidence is usually caused by the ground shrinking through a loss of moisture. This is more common after prolonged periods of dry weather. Areas where clay forms a significant proportion of the soil can be vulnerable, particularly where the clay is highly shrinkable as it then also has a tendency to expand when wet.
Other causes of subsidence may include:
- Absorption of moisture by trees and shrubs which can cause the water content of the ground to fall. For more information, see Tree root subsidence.
- Collapsing drains, culverts, hidden mine shafts, and so on.
- Buried organic material being which decomposes and destabilises all or part of a building’s foundations.
- Swallow holes or solution cavities.
- Improperly compacted ground.
- Sand or silt-based soils losing their water-soluble plant nutrients, in a process known as leaching.
 Methods of prevention and remediation
Tree Root Barriers made of high-density polyethylene can be a quick and cost-effective preventative method. As root growth can cause desiccation of soils, the use of barriers means that trees can be maintained and building occupiers not be unduly disrupted.
In minor cases of subsidence, re-pointing may be the only remedy required. If subsidence is more serious then the most common remedy is underpinning. This involves excavating soil from beneath existing foundations and replacing it with material, usually concrete, to form a new foundation beneath the existing one.
Research has shown that the majority of subsidence problems involve trees and vegetation to some extent. However, in practical terms it is very difficult to predict which trees will cause future problems. Removal of trees may not be desirable (due to the potential for heave), or may not be possible due to Tree Protection Orders (TPOs).
 Related articles on Designing Buildings Wiki
- Brownfield land.
- Contaminated land.
- Cracking and building movement.
- Defects in brickwork.
- Defects in construction.
- Defects in stonework.
- Ground conditions.
- Latent defects.
- Right of support.
- Tree root subsidence.
- Uplift force.
- Why do buildings crack? (DG 361).
 External references
Featured articles and news
This article examines the changing policy commitments and evolving definitions of the zero carbon home.
Researchers believe they may have created a 'game-changing' new form of concrete using graphene.
Grouting refers to the injection of materials into a soil or rock formation to change its physical characteristics.
Part of Designing Buildings Wiki, BREEAM Wiki will advance knowledge sharing for the BRE family of sustainability tools.
From the decorative to the utilitarian, and from the photographed to the forgotten.
New BRE book considers the progression from project-based knowledge creation to whole-life urban knowledge management.
This CIOB article explores the concept of value in building design and construction.
BREEAM and Measurabl announce integration to improve the financial performance of commercial real estate.
Rogers Stirk Harbour + Partners' release new images of soon-to-open 3WTC tower in New York.
A document can be called a bond or a guarantee. Does the name matter and what is the difference between them?
New briefing note is launched focusing on increasing knowledge of housing that promotes health and wellbeing.
Arbitration is a private, contractual form of dispute resolution used in the construction industry.