Home and living

The facts about subsidence

What is subsidence?

Subsidence is when the ground beneath a building sinks, pulling the property’s foundations down with it.

What causes subsidence?

Subsidence occurs when the ground loses moisture and shrinks, or the buildings’ foundations move. This can be caused by a number of things including:

  • Prolonged dry spells
  • Planting of trees and shrubs close to buildings, which absorb water from the soil causing ground cracking. Occassionally their roots will also grow so large that they can disrupt the foundations of the property
  • When the ground beneath a building moves upwards, which is called 'heave'
  • When the ground beneath a building moves down a slope, taking the property with it, which is known as a landslip or landslide

Key signs to look for...

Existing subsidence

The first sign is usually cracks in the walls, either internal plasterwork or external brickwork. Subsidence cracks are quite distinctive. They usually appear suddenly, especially after long spells of dry weather, and tend to be:

  • diagonal, and wider at the top
  • thicker than a 10p coin
  • found around doors and window

Subsidence can also cause doors and windows to stick as the building becomes distorted.

A property that’s been monitored for subsidence may have lots of small holes drilled into the outside.

Potential subsidence

Know the signs to look for when choosing a new property. There are 2 main culprits for causing subsidence:

Soil shrinkage

This kind of subsidence will be caused by the type of soil the property is built on. Typically there are 2 types:

  • Cohesive – generally clay or silt. They vary in their ability to adapt when wet or dry.
  • Non-cohesive - sand or gravel. These don’t adapt when wet or dry, but can be washed away when in a water flow.
  • In some cases, soil can be chalk or limestone which can dissolve over time, creating a cave. When these collapse it’s known as a ‘swallow hole’.

Man-made subsidence

This is caused by old in-filled sites where pits and quarries have been filled after mining and excavation has finished and covered over or vibration.

When it’s not subsidence

Many properties experience cracking, and this isn’t necessarily evidence of subsidence.

Buildings naturally shrink and swell in response to changes in temperature and humidity, leading to minor cracks where walls and ceilings meet. Nnew homes and recently built extensions also often experience cracking as the structures settle under their own weight. You might also notice fine cracks in freshly plastered walls as they dry out

If you're in any doubt, or have any concerns, contact a buildings expert, or you can find local trusted tradesmen on the TrustMark site.

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