Spotting a crack in your wall can be worrying, but not all cracks are created equal. Some are harmless and purely cosmetic, whilst others might indicate something more serious. This guide will help you understand what you’re looking at and whether you should be concerned.
The Main Types of Wall Cracks
1. Hair-Line Cracks
Concern Level: Low
These are very thin cracks (often just 1-2mm wide) that look like you could draw them with a pen. They’re typically found in plaster or render, which is the outer coating on your walls.
What they mean: Hair-line cracks are usually just surface-level damage caused by normal house movement, drying, or minor settling. They’re extremely common and rarely indicate a structural problem.
What to do: These are purely cosmetic and can be easily filled with filler and redecorated.
2. Vertical Cracks
Concern Level: Low
These cracks run straight up and down the wall, typically 2-5mm wide.
What they mean: Vertical cracks are usually caused by thermal movement—your walls expanding and contracting with temperature changes—or minor settling of the building. They’re common around window and door frames.
What to do: Keep an eye on them over a few months. If they’re not getting wider, they’re typically not serious. A professional can fill and repair them.
3. Horizontal Cracks
Concern Level: Medium
These run horizontally across the wall and can be quite wide (3-8mm or more).
What they mean: Horizontal cracks can indicate more significant movement or settling in your building. They sometimes occur above door and window openings where the structural load is concentrated. Wider horizontal cracks might suggest subsidence (when the ground beneath your home is shifting or sinking).
What to do: Monitor these closely. Measure the crack’s width and check it every few months. If it’s growing, contact a professional surveyor for advice.
4. Diagonal or Stair-Step Cracks
Concern Level: Medium
These cracks run at an angle across the wall, often in a zigzag pattern (particularly common in brick walls where they follow the mortar joints).
What they mean: Diagonal cracks typically indicate uneven movement or settling in your building. They’re more concerning than simple vertical cracks, as they suggest the structure is under stress.
What to do: It’s worth getting these checked by a surveyor, especially if they’re wider than 5mm or appearing in multiple locations.
5. Cracks with Displacement
Concern Level: Higher
These are cracks where one side of the wall has moved noticeably relative to the other. If you run your hand across it, you can actually feel a step or offset.
What they mean: This indicates significant structural movement and shouldn’t be ignored. It could suggest subsidence, foundation issues, or major settling.
What to do: Contact a structural surveyor as soon as possible. This warrants professional investigation.
6. Damp-Related Cracks
Concern Level: Higher
Cracks that are accompanied by damp patches, discolouration, or a musty smell. These might appear wider at the bottom and narrower at the top.
What they mean: Cracks allow moisture to penetrate your walls, which can cause significant damage over time and may indicate rising damp (water seeping up from the ground) or other moisture problems.
What to do: Get professional advice, as this likely requires both crack repair and damp treatment.
Quick Reference Chart
| Crack Type | Typical Width | Direction | Concern Level |
|---|---|---|---|
| Hair-line | Under 2mm | Random | Low |
| Vertical | 2-5mm | Up and down | Low to Medium |
| Horizontal | 3-8mm+ | Left to right | Medium |
| Diagonal/Stair-step | 2-10mm+ | Angled/zigzag | Medium to High |
| Displacement | Varies | Any direction | High |
| Damp-related | Varies | Any direction | High |
How to Assess a Wall Crack
When you spot a crack, check the following:
- Width: Is it thinner than a credit card (under 3mm)? Or noticeably wider? Use a ruler if unsure.
- Direction: Does it run vertically, horizontally, diagonally, or randomly?
- Location: Is it near a window or door, or in the middle of a wall? Movement around openings is common.
- Depth: Run your finger across it. Is it just surface-level, or does it go deep into the wall?
- Signs of moisture: Are there damp patches, discolouration, or mould nearby?
- Multiple cracks: Is this an isolated crack, or are there several appearing in different areas?