What is it?
Cracks that run at an angle across a wall, often wider at the top than the bottom.
What does it look like?
[Insert Photos] A slanted line cutting across bricks or plaster, frequently starting from corners of doors or windows.
Common causes
1. Subsidence (foundation sinking)
2. Heave (ground swelling)
3. Thermal expansion
4. Structural overloading
How serious is it?
Rating: High Concern. Diagonal cracks are the classic sign of structural movement and should always be investigated by a professional.
How to tell which cause you have
If the crack is wider than 3mm and passes through the bricks (not just mortar), it is likely subsidence.
What should you do next?
Instruct a structural engineer or a RICS surveyor to carry out a structural report.
Typical repair options
Underpinning, resin injection, or helical strapping.
Typical repair costs (UK)
£3,000 – £20,000+ if underpinning is required.
Frequently Asked Questions
1. Are all diagonal cracks subsidence? No, but many are.
2. What width is dangerous? Over 5mm is usually a major concern.
3. Do trees cause these? Yes, by drying out clay soil.
4. Will my house fall down? Unlikely, but it needs fixing.
5. Can I sell a house with these? Yes, but it’s harder.