Subsidence is less than ideal when you’re living in - or moving into - a property. But what is subsidence? Essentially, subsidence relates to the process of the ground beneath a building moving, which can then destabilise a property’s foundations.
What causes subsidence?
When thinking about what causes subsidence, there are a few things to keep in mind. 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 subsidence cracks. Occasionally, 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...
Some subsidence signs to look out for include:
The first subsidence sign you’ll notice is usually subsidence 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.
Knowing the subsidence signs to look for when choosing a new property will help you be in the know and aware of any issues. There are two main culprits for causing subsidence:
This kind of subsidence will be caused by the type of soil the property is built on. Typically there are two 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’.
This is caused by old in-filled sites where pits and quarries have been filled in with a variety of materials and covered over. The fill can degrade over time, usually due to the decomposition of the materials, causing a reduction in the volume of the soil. This then leads to subsidence.
When it’s not subsidence
Many properties experience cracking, and this isn’t necessarily evidence of 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. New 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 for a subsidence check.
Has your property previously suffered from subsidence or is it in a high risk subsidence area? Our expert non-standard property team can provide cover for all types of property, whether they have a history of flooding, subsidence or have been unoccupied long term.