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Cracks in your walls

If you’ve spotted a crack, find out whether it might be subsidence or one of the other far more common – and much less sinister – reasons that cracks form.

gocompare authors
Updated 15 September 2021  | 3 min read

Key points

  • Cracks appear on the walls of most homes. They are normally nothing to worry about and won’t affect the stability of your property.
  • Harmless, cosmetic cracks can be caused by anything from your home ‘settling’ to temperature changes.
  • Subsidence and heave are the most serious causes of cracks appearing in your home.
  • Cracks caused by these sorts of ground movements are typically much larger – more than 5mm wide -and often run diagonally.

When should you worry about cracks in your walls?

Although some cracks are warning signs that the ground beneath a building is shifting and causing structural damage, most are harmless.

Common causes of minor cracks include:

Settlement

All new buildings – or new extensions to homes – settle downwards under their own weight. This can cause cracking without any threat to the structure.

Usually, settlement cracks appear at weak points, like around windows.

It can take up to 10 years for a building to settle, so you can expect some minor cracks to appear in new builds for quite some time.

Temperature and humidity

All buildings, new and old, expand in the heat and contract in falling temperatures. You may have even heard creaks or snapping sounds as these movements occur.

Thermal cracks caused by this sort of movement are minor and easily repaired.

In newly-built homes, moisture in building materials like wood, concrete and mortar dries out over several months. This results in some shrinkage, which can lead to cracks, usually near ceilings and floors.

In homes old and new, cracks can appear when building materials expand and shrink depending on how much moisture is in the air.

Materials expand as they absorb the water vapour that’s expelled in our homes when we take baths and showers, or boil kettles and cook, for example. Then they shrink as they dry out when it’s warm outside or when the central heating is on.

Cracks can also be caused by:

  • Water damage
  • Vibrations from heavy traffic or construction work
  • Ageing and wear and tear
  • Freshly plastered walls drying out or ‘blown’ plaster

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What size cracks should I be concerned about?

Minor cracks that measure no more than 2mm are usually nothing to worry about and will have no effect on the safety and stability of your property. You can easily check the width of cracks with a measuring tape.

But you should investigate further cracks that:

  • Measure more than 2mm wide along their full extent, especially those that run diagonally.
  • Are more than 5mm wide at any point in the crack.
  • Are wide at one end and narrow at the other.
  • Can be seen on both inside and outside walls.
  • Have become wider or longer over time.

These sort of cracks could be a sign of structural damage and subsidence.

When are cracks in walls a sign of a problem with the structure itself?

Subsidence happens when the ground beneath a property erodes and moves downwards.

As the ground sinks, it pulls the property’s foundations down with it, damaging its structure and causing cracks.

Heave, on the other hand, is when the ground moves upwards, or swells, causing a property to lift. It’s less common than subsidence.

Heave and subsidence can occur when soil gets too wet due to flooding, or too dry due to excessive periods of drought.

These type of ground movements tend to happen in:

  • Areas that have peat or soft clay soil
  • In homes built where mining has taken place in the past
  • In properties with poor drainage or those that are surrounded by trees and shrubs that absorb excessive moisture from the soil

As well as wide cracks appearing, signs of subsidence can include:

  • Gaps appearing between the floors and walls
  • Sloping, uneven floors
  • Cracks in concrete floors and in garden paths
  • Doors and windows that become difficult to open and close tight
  • Cracks that appear on exterior brick walls that are zig-zagged and follow the lines of mortar

How can I prevent cracks appearing?

In a newly-built home, you can help to keep cracks at bay by allowing building materials to dry out gradually so that shrinkage is not too sudden.

Try leaving window vents open to allow for natural evaporation of moisture and avoid cranking up the central heating too high as excessive heat can speed up the drying process and cause cracking.

If you live somewhere that’s prone to subsidence issues – such as a clay soil area – there are some things you can do to try to help prevent the problem.

  • Avoid planting large trees or shrubs that will dry out soil close to your home. If you already have a tree close to your property, get specialist advice before removing it, though. In some cases, if a well-established tree is removed, moisture in the ground will build up and could cause the ground to swell, resulting in heave, which can damage your property further.
  • Keep close checks that pipes, drains, gutters and plumbing are not leaking, as this can wash away soil.

How can I fix cracked walls?

When you next decorate, you can easily repair minor cracks using a filler, then lightly sanding before applying paint.

What should I do if I'm worried about cracks in my walls?

If you suspect subsidence, you should contact your insurer.

They may send out a building specialist or surveyor to take a look.

The specialist might want to place monitors onto cracks to check for ongoing movement and to assess the ground below the foundations.

If movement of your home has stopped, then repairs to damage can go ahead.

If movement is ongoing and is causing major structural damage then you may need to have your home underpinned. This involves lifting, re-levelling and strengthening the ground underneath the building.

Does home insurance cover cracked walls?

Small, hairline cracks are normal as a newly built property settles, or as any home ages and is lived in.

Such minor cracking is a cosmetic problem, and any repairs needed won’t be covered by buildings insurance.

Cracks that form as the result of subsidence, though, are usually covered by an insurance policy.

This is true only if your home has not suffered subsidence in the past (though there are some specialist insurance policies that will cover properties with subsidence history.)

Your buildings insurance policy will cover the cost of repairing damage to the structure of your home that occurs as the result of subsidence, including the repair of cracks.

It won’t normally cover the cost of preventing further subsidence and movement of your home though.

Some policies offer to meet the cost of your accommodation should you need to move out of your home if it needs extensive repair.

Subsidence claims usually come with an excess in the region of £1,000.

Will claiming increase my premium?

Premiums and excesses can increase after you’ve made a subsidence claim with your insurer, especially if it’s still at risk of further movement.

Some companies won’t insure you at all if your home has had subsidence issues as they see it as too much of a risk.

You may need to shop around for specialist insurers who will cover you.

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