Cracks in walls and subsidence: what homeowners need to know

Noticing a crack in your wall can be unsettling, especially if you own your home. The good news is that many cracks are completely normal. But some can point to more serious structural problems, including subsidence.

This guide explains what different types of cracks mean, when to take action, and what it could mean for your home insurance.

Key takeaways:

• Small, hairline cracks in walls are normal and usually nothing to worry about.
• Minor wall cracks are typically caused by movement, temperature changes or a building settling over time.
• Wide, diagonal or stepped cracks can be a sign of subsidence and should be investigated.
• Buildings insurance typically includes cover for subsidence as standard.
• Professional advice is the safest option if you’re unsure about a crack.

Are cracks in walls normal?

Minor cracks can appear in walls for all kinds of reasons, and many are harmless.

Homes expand and contract with the seasons. Plaster dries out, and new builds settle as the ground adjusts to the weight of the structure. All of this can cause small cracks to appear over time.

That doesn't mean you should ignore every crack you see. Some cracks can be a sign of structural issues that need attention. The key is knowing the difference between a cosmetic crack and one that needs checking.

What causes cracks in walls?

There are several common reasons cracks appear.

• Thermal movement: Walls expand in heat and contract in cold. Over time, this repeated movement can cause small cracks, especially around windows and doors.
• Drying shrinkage: In new builds, concrete and plaster lose moisture as they cure. This often causes fine surface cracks in the first year or two.
• Settlement: Most properties settle slightly after they're built as the ground adjusts beneath them. This is normal and usually stops after a few years.
• Moisture and damp: Water can weaken plaster and masonry, which may cause cracking. This is worth investigating separately. Our guide to damp and home insurance explains more.
• Subsidence: When the ground beneath a property shifts or sinks, it can cause the foundations to move. This is the most serious cause of cracking and is covered in more detail below.
• Poor building work: Extensions or structural changes carried out without proper care can cause cracking in nearby walls.

Different types of cracks in walls

Not all cracks are the same. The shape, direction and location of a crack can tell you a lot about what's causing it.

• Hairline cracks: Very thin surface cracks, usually less than 1mm wide. Common in plaster and almost always harmless. Often caused by drying or minor temperature changes.
• Vertical cracks: Cracks that run straight up and down the wall. Usually caused by normal settlement or temperature changes. Narrow vertical cracks are generally low risk, but wider ones near structural areas are worth monitoring.
• Diagonal cracks: Angled cracks, often starting from the corners of doors and windows. These can be a sign that one part of the building is moving more than another. If they widen over time, get them checked.
• Horizontal cracks: Cracks that run across the wall. These can be more serious, especially in external brick walls. They may indicate the wall is under pressure or bowing. This warrants a professional inspection.
• Stepped cracks: Cracks that follow the mortar joints in a staircase pattern, usually in brick or blockwork. These are often linked to subsidence or foundation movement and should be taken seriously.
• Cracks wider than 5mm: Any crack wider than 5mm, regardless of direction, is worth getting looked at. Cracks over 15mm are considered severe and need urgent attention.

When to worry about cracks in walls

Many cracks don't need immediate action, but there are some signs that a crack is more than cosmetic.

You should get professional advice if:

• The crack is wider than 5mm
• The crack is growing or changing shape over time
• Doors or windows are sticking or no longer closing properly
• Floors feel uneven or are sloping
• Cracks appear in multiple places at the same time
• You can see daylight through a crack in an external wall
• The crack is stepped or horizontal in brickwork

If you notice any of these signs, contact a structural engineer or a Royal Institution of Chartered Surveyors (RICS) surveyor. They can recommend what to do next.

What is subsidence?

Subsidence is when the ground beneath a property sinks or shifts, causing the foundations to move. This movement puts stress on the structure of the building, which can cause cracks.

It's different from settlement, which is the gradual adjustment a building makes in its early years. Subsidence is uneven and can affect older properties too.

Causes of subsidence

Common causes of subsidence include:

• Clay soil: Clay-heavy ground shrinks during dry spells and swells when wet. This repeated movement can destabilise foundations.
• Tree roots: Large trees near a property can absorb moisture from the ground. This can dry out and shrink clay soil beneath the foundations.
• Leaking drains or pipes: Water from a damaged drain can wash away the soil beneath a building, creating gaps below the foundations.
• Drought: Extended dry periods can cause significant soil shrinkage, particularly in clay-heavy areas.
• Mining or construction nearby: Underground work can disturb the ground and affect nearby properties.

What does subsidence look like?

The signs to look for include:

• Diagonal or stepped cracks, especially around door and window frames
• Cracks that are wider at the top than at the bottom
• Doors and windows that stick or have started to fit poorly
• Visible gaps between walls and floors or ceilings
• Wallpaper wrinkling where walls and ceilings meet

Monitoring is important. Mark the ends of any cracks with a pencil and the date, then check them regularly to see if they're growing.

A RICS surveyor can also carry out a formal assessment. If you suspect subsidence, it's important to act sooner rather than later.

Can subsidence be fixed?

In many cases, yes. The right solution depends on the cause and the severity.

Common fixes include:

• Removing or cutting back trees: If tree roots are the cause, removing or pruning the tree can stop the soil drying out. It may take time for the ground to stabilise afterwards.
• Repairing drains: If a leak is washing away soil, fixing the drain is the first step.
• Underpinning: For serious cases, the foundations may need to be strengthened. This involves digging below the existing foundations and filling the space with concrete to create a more stable base.
• Resin injection: This is a less disruptive alternative to underpinning. Resin is injected into the ground to stabilise the soil.

Once the cause has been addressed, cracked walls can then be repaired.

Good ongoing home maintenance can help prevent problems from developing in the first place. Our guide to home maintenance and risk prevention has practical advice on keeping your property in good shape.

Subsidence and home insurance: what you need to know

Subsidence damage is typically covered under buildings insurance as standard. If your home is affected, you can make a claim to cover the cost of repairs to the structure of the building.

What is subsidence excess?

An excess is the amount you pay towards a claim before your insurer covers the rest. It is usually higher for subsidence claims, often £1,000 or more.

This is because subsidence claims tend to be expensive, so insurers set a higher excess. It's worth checking what your subsidence excess is before you need to make a claim.

How long do you have to declare subsidence?

You must declare any known subsidence, past or present, when you take out or renew a home insurance policy. Failing to disclose it could invalidate your insurance.

If your home has had subsidence in the past and it has been fully repaired, you still need to declare it.

Some insurers may charge a higher price as a result, but many will still offer cover. Being upfront from the start helps protect you if you ever need to make a claim.

How does subsidence history affect your insurance?

A history of subsidence can make it harder to get cover, and it may affect your price.

If you're buying a home with a history of subsidence, it's worth getting a full structural survey before you complete and making sure you understand the insurance implications.

Our guide to how much home insurance costs covers the factors that affect your price in more detail.

How Marshmallow can help

At Marshmallow, we offer home insurance designed for people who are new to the UK.

Our buildings insurance covers subsidence as standard, so if the ground beneath your home shifts and causes structural damage, you're protected.

Get a home insurance quote with Marshmallow.