21 October, 2021 | Building Survey

When does a crack in the wall indicate subsidence?

If you want to know if the property you are thinking of buying is in good condition, an independent surveyor should be your first port of call. Nowhere is this more important than if there’s a crack in the wall. Let’s be honest – the untrained eye won’t be able to tell if a crack is a simple decorating job or whether it’s an indication of a major structural issue with the building. For the sake of your investment, we urge you to have a property survey carried out, so you know exactly what you’re dealing with.

At SSJ Surveyors, we have over 20 years professional experience in carrying out surveys for residential property as well as commercial premises, including the full range of RICS home surveys. Our RICS Building Surveys and Building Defect Reports are designed to inspect all visible building elements, providing in-depth professional advice to empower the homebuyer to make an intelligent purchase decision. While most minor surface cracks are usually nothing to worry about, cracking that has occurred as a result of structural movement could well turn out to be a serious issue.

Why do cracks in walls usually appear?

Before we go any further, it’s worth saying that cracks in the walls of houses are by no means uncommon. In fact, most properties have them at some point. Hopefully, this will provide some reassurance. Cracks occur naturally as a result of settlement, such as in these scenarios:

  • New build homes and building extensions have foundations that may need time to settle under their own weight. Hairline cracks may appear as a result.
  • Hairline cracks can also appear on freshly plastered interior walls, while the walls take time to dry out.
  • In older properties, temperature and humidity changes may lead to a slight expansion and contraction, which is perfectly normal.
  • UPVC double glazed window replacements for timber windows that don’t have a supporting lintel may lead to cracking around the window.
  • Properties on busy roads may experience cracks in walls as a consequence of road traffic vibration.

When should you worry?

Cracks like those mentioned above are usually superficial in nature, requiring nothing more than painting and decorating to get rid of them. Larger cracks, on the other hand, may indicate a more sinister and far-reaching problem. They could be a sign of structural movement of the building’s foundations which can lead to serious damage. The worst-case scenario is that the building’s structural integrity becomes so unstable that it could collapse.

Structural cracks may be caused by:

Tree Roots

If tree roots get under the foundations, they absorb moisture from the soil underneath the property which can destabilise the building. Large trees less than 10 metres from the building should be urgently inspected. Willows, oak trees, poplar and ash are known to be particularly ‘thirsty’ tree species.

Dry Spells

Prolonged heatwaves and dry spells are particularly dangerous for homes built on clay soil. This porous soil shrinks when dry, pulling away from the foundation. Did you know that home insurance claims for subsidence tripled after the dry summer of 2018?

Heavy Rain

Heavy rainfall and flooding can have dire consequences, particularly if the house is built on clay soil. Subsidence on clay soil is usually seasonal, involving shrinkage during hot, dry summer months and expansion during the wetter winter season.

Defect Drains

Burst pipes or leaky drains can remain undetected for a long time while damaging the building, either by washing away the subsoil or by saturating the ground. Either way, the weight of the building may no longer be able to be properly supported.

How can you tell a ‘wide’ crack in the wall?

If you’re not sure whether the crack in a building is serious, the width of the crack could be an important indicator. As a general rule, cracks that are wider than 15mm or that have appeared suddenly may well be a cause for concern and should be looked at by a surveyor or structural engineer, who will report them as falling into one of the following categories:

Negligible: These are hairline cracks under 1mm wide that can easily be eliminated by redecorating.

Slight: Cracks that are between 1-5mm in width can be remedied by way of interior filler / external repointing.

Moderate: Cracks that are between 5-15mm wide may need a professional plasterer or building contractor for repair.

Severe: Large cracks that are up to 25mm in width may be an indicator of structural damage and should always be inspected by a professional surveyor.

Very Severe: Cracks wider than 25mm are usually a clear sign of advanced subsidence. The building may need underpinning or rebuilding and professional assistance is required asap.

Large vertical cracks or diagonal cracks that are wider at the top than at the bottom of a wall are tell-tale signs of structural movement. They are most often found around windows and doorways but can appear anywhere.

If you are concerned about cracks in the wall of a property you are thinking of buying, it is prudent to seek professional advice at the earliest opportunity. Get in contact with the Chartered Surveyors at Silk Sharples Jennings by calling 01743 461777 or emailing info@ssjsurveyors.co.uk and let our expertise and experience inform your property purchase.

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