Why do cracks in walls appear?

Most cracks are normal in homes, even in new builds. They’re typically caused by several factors including natural building movement, changes in temperature or settlement over time. Cracks in walls can also appear if there are structural issues such as subsidence.

Common causes of cracking walls

Understanding the common causes of cracks in walls, from the non-serious to potentially serious, can help determine if the issue requires further investigation.

Non-serious

• House settling

• Newly dried plaster

• Seasonal soil shrinkage or expansion (especially with clay soils)

• Thermal expansion and contraction

• Lack of lintel (beams that provide load bearing support)

Potentially serious

• Nearby tree roots (growing and drawing moisture from soil)

• Water damage or leaky drains

• Poor ground support

• Ageing building or materials

• Nearby heavy traffic

Common types of wall cracks

Your first instinct may be to panic when you see a crack in your wall, but it’s important to understand what you’re looking at. Here are the most common types of wall cracks and what they usually mean.

Hairline cracks

Hairline cracks in walls are common and are usually found around doors and windows. These cracks are typically cosmetic, often caused by plaster shrinkage or paint movement and normally aren’t something to worry about.

Vertical cracks

If you notice vertical cracks, they may be the result of foundation settlement. These are often found in areas where the walls meet ceilings or floors. Wider cracks of more than 5mm may requirement assessment.

Horizontal cracks

If the cracks appear horizontally, there may be pressure on the walls from soil or ground movement. If they appear externally, then it may be due to retaining wall stress or shifting foundations and should be assessed quickly.

Diagonal cracks

Diagonal cracks, which may widen towards the top or bottom of the wall, are frequently associated with subsidence or foundation movement. These cracks should be taken seriously, especially if they’re near doors and windows.

Step cracks in brickwork

Zig-zag cracks that follow mortar lines are a common sign of subsidence. These are especially concerning if they reappear after repair or worsen over time and should be investigated as soon as possible.

Ceiling and door frame cracks

Cracks which appear here may suggest even house movement and settlement. Temperature changes and expansion of timber frames can also affect this. These are worth monitoring over time, as if they worsen then it could indicate ground movement.

Cracks that keep coming back

Recurring cracks are an indicator that the underlying ground movement hasn’t been fixed. While patching over cracks can help with cosmetic issues, it won’t help fix the problem if the cause is a structural issue. Mainmark’s subsidence and ground improvement treatment methods effectively fix cracks in walls in properties of all sizes.

When to worry about cracks in the wall

So, what should you do if you’re concerned about cracks in walls? Firstly, you should make a note of the size and type of cracks and keep a record of where and when they appear.

You should act if:

• Cracks are wider than 5mm or keep widening

• They appear suddenly or after heavy rain/dry weather

• They run diagonally through door or window frames

• You notice uneven floors, sticking doors, or gaps at skirting boards

• Doors and windows have gaps around their frames

• Two sides of a wall are at differing heights

• Cracks extend from inside to outside walls

What to do next:

• Monitor the cracks for changes (mark and date the edges).

• Take clear photos for reference.

• Don’t fill or repaint until assessed.

• Contact a professional. Mainmark can identify whether the issue is cosmetic or structural. If you’re worried you may have subsidence, book a survey with us today.

What Causes Structural Cracks in the UK?

Subsidence and drainage issues are common causes of cracks in walls. Tree roots too can cause problems as they grow and branch out in search of moisture. Many parts of the UK, particularly London and the South-East, have clay-rich soils. That means that during spells of heavy, prolonged rain, the soil swells and expands and during a heatwave the soil loses its moisture quickly causing it to contract and shrink. This constant movement causes the ground beneath the property to shift and puts stress on the foundations, resulting in cracked walls and ceilings.

It's important to note that many older homes naturally settle and so not all cracks are a sign of danger. Early diagnosis, however, prevents costly repairs. Find out more about Mainmark UK’s residential subsidence solutions.

When it’s time to call an expert

Identifying the root cause of cracked walls and ceilings is essential to fixing the problem. If there’s ground movement, then patch repairs won’t resolve the issue. Mainmark offers a range of proven solutions including Teretek® Resin Injection, a non-invasive method where an inert resin formulation is injected beneath the foundations to fill voids, improve soil, and restore load-bearing capacity. It’s fast, effective and work can be done with minimal disruption allowing occupants to stay in their homes.

An example of this is a three-storey semi-detached London house extension, which suffered subsidence, pulling 35mm away from the main building and causing structural damage. Mainmark resolved the issue by using resin injection and precision computer-controlled grouting (JOG). This raised the extension by 21mm without major excavation or disruption, meaning residents were still able to use the whole house as works were carried out.

Worried about cracks in your home?

Not all wall cracks are a cause for concern. Some are cosmetic and are typically caused by natural settling and temperature and moisture changes. However, cracks that are wider than 5mm, run diagonally, horizontally, or reoccur may signify deeper structural issues such as subsidence or ground movement.

Early investigation can help the problem before it becomes severe. Mainmark, can help identify the root cause and provide long-lasting, non-invasive solutions to stabilise foundations and prevent further damage.

If you’re concerned about the cracks in your walls, contact us today.

FAQs

Are small hairline cracks in walls normal?

Yes, hairline cracks are considered normal and are often the result of cosmetic issues such as natural building settlement, expansion and contraction due to temperature changes and age of the building.

When should I be worried about wall cracks?

Cracks wider than 5mm, appear suddenly after heavy rain or dry weather, or run diagonally through door or window frames are a cause for concern. Uneven floors, sticky doors, gaps in the skirting boards are also indicators of a structural problem.

What does it mean if cracks keep coming back?

Recurring cracks indicate that the underlying issue hasn’t been resolved. Mainmark UK subsidence and ground improvement treatment methods effectively fix cracks in walls in properties of all sizes

Who should I contact about structural cracks?

Ground engineering experts can assess the extent of the problem and find an appropriate solution. Mainmark’s ground improvement treatment methods can address foundation subsidence and are effective in fixing cracks in walls or re-levelling sunken floors.