Subsidence


What is subsidence?

Subsidence involves the downward shift of a building’s foundations in line with ground movement.  This occurs as a result of changes in the moisture content of the soil leading to shrinkage.
Heave, by contrast, involves upward ground movement and a corresponding movement in foundations.  This occurs when dry soil swells due to increased moisture or usually as a result of mature trees being removed.

What causes subsidence to occur?

Changes in ground conditions resulting from:-

  • changes in weather patterns coupled with increasingly dry Summers
  • vegetation; trees and shrubs can extract moisture from deep within the soil causing shrinkage, especially during long period of dry weather
  • removal of trees and shrubs can cause previously dry soil to swell up resulting in heave
  • defective / leaking drains causing soil erosion beneath a buildings foundations 
  • clay soil, which is more susceptible to shrinking and swelling according to moisture content  

What are the signs?

The first obvious sign of subsidence is diagonal cracking. 
Most houses suffer minor cracking when buildings shrink and swell naturally due to changes in temperature and humidity, in plasterboard joints and where walls meet ceilings.  These cracks are normally nothing to worry about.
The warnings signs are when a series of small, diagonal cracks suddenly appear in plasterwork finishes and around openings which are potentially weak points.  This type of cracking will normally appear following a long dry spell and the cracks are normally wider at the top than at the bottom. 

What should you do?

If you suspect your home may have subsidence you must contact your buildings insurer straight away.  Alternatively, if you suspect the home you may be purchasing may be suffering from subsidence, you will need to commission a Structural Engineers Report to identify if there is a problem. 

 What can you do to prevent subsidence?

The most obvious preventative measure is to control the growth of any existing trees and shrubs;  

  • take care when planting any new trees / shrubs
  • as a general rule, any new trees need to be planted the same distance away from you house as their expected mature height
  • think carefully before selecting any new trees to plant, the broad leaf varieties tend to cause more damage than evergreens because of the amount of moisture they require
  • prune existing trees and shrubs regularly to keep them to a sensible height 

Other preventative measures;

  • check for blocked or leaking drains 
  • check gutters regularly and clean out leaves & dirt 
  • check pipes, particularly during cold spells to ensure no damage or leaks

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