It’s natural to feel worried when you spot a crack in your wall. The question that runs through most people’s minds is simple: is this serious?
In this guide, we’ll help you work out whether you need to take action or whether you can relax and move on.
The Honest Truth
Most wall cracks are not cause for concern. Houses settle, materials expand and contract, and minor surface cracks happen all the time. However, some cracks do warrant attention. Learning to tell the difference is key.
Size Matters
The width of a crack is one of the best indicators of whether you should be worried.
| Crack Width | Concern Level | What It Means | Action |
|---|---|---|---|
| Under 3mm | Low | Minor surface damage from normal settling or drying | Monitor, purely cosmetic |
| 3-5mm | Medium | Moderate movement in the building | Keep an eye on it, track any growth |
| 5-10mm | High | More significant movement occurring | Get professional assessment |
| Over 10mm | Very High | Substantial structural movement | Professional survey needed soon |
Wall Crack Guide By Size
- Hairline to 3mm (under 1/8 inch): These tiny cracks are extremely common and rarely a problem. They typically indicate minor movement or drying in the plaster or render. You can usually live with these without any issues. They’re a cosmetic concern rather than a structural one.
- 3-5mm (roughly 1/4 inch): This is the middle ground. A crack this size might need monitoring but isn’t necessarily an emergency. If it’s vertical or only in one location, it’s likely still low risk. However, if you have multiple cracks this size or if it’s horizontal, you should keep a closer eye on it.
- 5mm and above (over 1/4 inch): Once cracks reach this width, they deserve proper attention. Particularly if they’re horizontal, diagonal, or appear in several places around your property. It’s worth getting these assessed by a professional.
The Growth Factor
Here’s something many homeowners don’t realise: it’s not always the size of the crack that matters most, but whether it’s getting bigger.
| Time Period | What to Look For | What It Might Mean |
|---|---|---|
| Week 1-4 | Any visible change at all | Actively developing issue |
| Month 1-3 | Steady widening or lengthening | Ongoing movement in the building |
| Month 3-6 | Growth has stopped or slowed | Likely stabilising |
| 6+ months | No change from earlier measurements | Probably stable and low risk |
A stable crack that hasn’t changed in size for months or years is far less concerning than a crack that’s visibly growing. A crack that’s stayed the same size for two years is probably just cosmetic damage. A crack that’s widened noticeably in the last few weeks could indicate an ongoing issue.
To track this yourself, try these simple methods:
- Take a photo of the crack with a ruler next to it. Date the photo and repeat monthly.
- Use a piece of tape across the crack and mark where the edges are. Check back in a month to see if it’s crossed your marks.
- For very fine cracks, hold a piece of paper behind it. If you can see light through it, it’s definitely worth monitoring.
Crack Location Matters
Where a crack appears on your wall can give you important clues about what’s causing it.
Around Windows and Doors
Cracks in these areas are very common. These are stress points where the structure bears weight, and they’re prone to movement. Small cracks here are usually not a major concern, though they might need redecorating.
In Corners of Rooms
Corner cracks often indicate settling or minor movement. Again, these are usually low risk unless they’re quite large or growing rapidly.
Running Across the Entire Wall
A crack that runs a long distance (especially horizontally) should be taken more seriously than a short, localised crack. This suggests wider movement in the building.
In the Foundation or Basement
Any significant cracks in basement walls or at ground level warrant professional attention, as they could relate to foundation issues or water ingress.
Multiple Cracks Appearing Simultaneously
If you suddenly notice several new cracks in different parts of your property, this is worth investigating. It might indicate a more widespread issue than a single crack.
Other Warning Signs
Beyond just the crack itself, watch out for these accompanying signs:
Damp or Moisture
If the area around the crack feels damp, looks discoloured, or smells musty, that’s a red flag. Moisture and cracks together need professional attention.
Doors or windows sticking
If doors or windows near a crack are suddenly difficult to open or close, it might indicate structural movement. This is worth getting checked.
Cracks Appearing in Other Materials
If you notice cracks appearing in brickwork, ceiling plaster, or tiles at the same time, it suggests the building itself is moving. This warrants professional assessment.
Visible Displacement
If you can actually see that one side of the crack is higher or lower than the other, or if the wall surface is noticeably stepped, that’s a more serious sign.
Crumbling Plaster or Mortar
If the edges of the crack are crumbling or the surrounding area is deteriorating, it’s worth having it looked at.
When to Call a Professional
Use this checklist to decide if professional advice makes sense:
| Situation | Should You Call? | Why |
|---|---|---|
| Single hairline crack, no growth | No | Almost certainly cosmetic |
| Crack wider than 5mm | Yes | Needs proper assessment |
| Crack growing visibly over weeks | Yes | Indicates ongoing movement |
| Multiple cracks in different areas | Yes | Suggests wider building issues |
| Crack with damp or moisture | Yes | Urgently needs investigation |
| Visible displacement (stepped surface) | Yes | Indicates structural movement |
| Doors/windows sticking near crack | Yes | Sign of movement affecting structure |
| You’re unsure or anxious about it | Yes | Peace of mind is valuable |
You should consider getting professional advice if:
- The crack is wider than 5mm
- The crack is growing or changing noticeably over weeks
- You have multiple cracks across your property
- The crack is accompanied by damp or moisture issues
- There’s visible displacement along the crack line
- Doors or windows near the crack are sticking
- You’re simply unsure and would feel better having it checked
A professional surveyor or structural engineer can give you proper peace of mind. They can assess whether the crack is cosmetic or structural, identify the underlying cause, and recommend the right fix.
What You Can Do in the Meantime
While you’re deciding whether to call someone in, here are some practical steps:
- Take measurements and photos to track any changes
- Keep an eye on the crack monthly
- Check for any signs of moisture
- Don’t ignore it completely, but don’t panic either
- Talk to your neighbours. If they have similar cracks in similar properties, it’s likely just normal settling