Diagonal Cracks in Property: Warning Signs or Investment Opportunity?

Cracks in walls are a common sight when inspecting properties—but when should you really start to worry?

Crack monitoring studs visible on both sides of the crack

Hairline cracks can arise from various factors like settlement or thermal expansion, but if a crack is diagonal, it’s time to take a closer look.

Why Diagonal Cracks Matter?

Diagonal cracks suggest movement in the structure at 90° to the crack itself, often this suggests a downward movement—a potential red flag.

The biggest concern? Foundation movement, also known as subsidence. This occurs when the ground beneath a property sinks or shifts. Key causes include:

• Tree roots damaging nearby drains, washing away supporting soil (especially in sandy areas).

• Roots of trees or bushes near foundations causing mechanical damage or drying out soil.

• Seasonal changes, particularly on clay soil, where cracks may appear in dry weather but close up again when moisture levels increase.

• Underground mining, a particular concern in former coal mining areas.

  
  

Diagonal cracking through a passageway wall

The Risks of Structural Movement

Diagonal cracks can indicate serious and costly problems, including:

• Structural Instability – If left unchecked, movement can compromise a building’s safety.

• Water Infiltration – Cracks allow dampness and mould to take hold, worsening structural issues.

• Lending Refusal – Mortgage lenders may assign a zero valuation and require an expert report from a Chartered Building Surveyor or Structural Engineer.

• Reduced Property Value – Structural concerns deter buyers and can drive down resale prices.

• Rising Repair Costs – The longer movement continues, the more expensive the fix.

  
  

What Should You Do?

If you come across diagonal cracks, take action promptly:

1. Get a Professional Inspection – A Chartered Building Surveyor or Structural Engineer can, in the first instance, assess whether the cracks are historic or ongoing.

2. Monitor Movement – Ongoing movement needs tracking over 12-18 months using crack width gauges - the key is to establish if movement is progressive (hopefully not!).

3. Foundation Repair – Solutions like underpinning or mini-piling may be required if subsidence is confirmed.

4. Flexible Repairs – Use lime mortars, flexible sealants and heavy-gauge lining papers to accommodate small future movements.

5. Preventative Maintenance – Regular property inspections, drain checks, and careful tree management can help prevent further cracking.

Investor Tips: When to Walk Away & When to Seize an Opportunity

For property investors, knowledge is power. Here’s how to approach properties with structural movement:

1. Always get a full structural survey before purchase—you need all the facts upfront.

2. Get a Coal Mining Report —subsidence is usually less severe when mining was deeper than 100m, as movement stabilises within a few years.

3. Know that cash is king – Properties with suspected subsidence issues often get a zero valuation, meaning they become cash-only deals—great for negotiation and eliminating mortgage-backed competition.

4. Have a Structural Engineer on your team – They’re invaluable for cracking assessments, monitoring, and overseeing remedial works like underpinning.

5. Look for tell-tale signs – Diagonal cracks are usually wider at the top than the bottom and often appear around doors and windows. Accompanying signs include sticking doors, sloping floors, and gaps between walls and ceilings.

6. Check the drains when viewing a property with suspected movement. That means opening the inspection chambers inside the plot, checking pipe and chamber condition and flushing water through the system making sure it all drains away.

Conclusion

Diagonal cracks in a property should never be ignored. They often signal deeper structural issues that require expert assessment and, in some cases, long-term monitoring. Repairs can be costly, and not all properties are worth the risk.

However, if you have the right professionals on your team, a structurally compromised property can present a lucrative opportunity—especially when others are too afraid to take it on.

If you’re serious about investing in UK property and want expert guidance on sourcing solid investments (without the hidden nightmares), get in touch. We help investors build strong portfolios—without costly surprises.