Causes of Flat Roof Leaks

Understanding what causes flat roof leaks is the first step to protecting your property. Whether you manage a commercial building or own a home in London, identifying the source of water ingress early can save thousands in repair costs.

Why Flat Roofs Are More Prone to Leaks

Flat roofs are a practical choice for modern buildings, offering easy access and space for HVAC systems, skylights, and solar panels. However, their minimal slope means water doesn’t drain as quickly as on pitched roofs — increasing the risk of pooling, membrane stress, and eventual leaks.

1. Ponding Water and Poor Drainage

One of the leading causes of leaks is standing or “ponding” water that doesn’t drain within 48 hours after rain. Blocked outlets, poorly designed slopes, or debris buildup can allow water to collect and slowly penetrate weak points in the roof membrane.

• Blocked gutters and outlets from leaves or debris

• Incorrect roof gradient during installation

• Insufficient drainage capacity for heavy rainfall

2. Damaged or Aged Roofing Membrane

Over time, exposure to UV rays, temperature fluctuations, and foot traffic can weaken the membrane surface. Cracks, blisters, or shrinkage allow water to enter beneath the protective layer, leading to hidden leaks and insulation damage.

• EPDM rubber shrinkage or splits

• TPO and PVC seams separating over time

• Bitumen blistering caused by trapped moisture

3. Faulty Flashing and Roof Penetrations

Flashing protects the vulnerable joints between the roof and vertical surfaces such as walls, skylights, and vents. When flashing becomes loose, corroded, or improperly sealed, it allows water to enter through gaps around roof penetrations — one of the most common points of failure on commercial buildings.

4. Poor Installation or Workmanship

Even high-quality materials can fail if the roof wasn’t installed correctly. Inconsistent seams, inadequate adhesive application, or poor detailing around penetrations can all lead to premature leaks. Always verify that installers are accredited and experienced in commercial flat roofing systems.

5. Roof Traffic and Equipment Damage

Commercial flat roofs often host HVAC systems, satellite dishes, and maintenance walkways. Foot traffic and dropped tools can puncture the membrane, while vibration from machinery may weaken seals over time. Protecting walkways and restricting access are simple ways to reduce accidental damage.

6. Thermal Movement and Weathering

London’s changing weather causes materials to expand in summer and contract in winter. This constant movement puts stress on seams, adhesives, and flashing — eventually creating cracks that allow water in. Extreme temperature shifts, snow, and UV exposure accelerate this deterioration.

7. Structural Movement or Subsidence

Buildings naturally settle over time, but excessive movement can distort a flat roof’s surface and cause gaps in the waterproofing layer. This often appears as splitting or wrinkling in the membrane, particularly near joints or parapet walls.

8. Inadequate Maintenance

Neglect is a major contributor to leaks. Without regular inspections and cleaning, minor defects go unnoticed until water finds a way through. Routine maintenance ensures debris is cleared, joints are resealed, and early signs of wear are addressed before damage becomes serious.

• Annual or biannual inspections recommended

• Immediate attention after storms or heavy rainfall

• Professional cleaning to prevent moss and debris buildup

How to Prevent Flat Roof Leaks

Prevention is always better than repair. Scheduling routine inspections and addressing drainage or membrane issues early can significantly extend the lifespan of your roof. Professional flat roof leak detection services use infrared and electronic testing to locate moisture before it causes interior damage.

Serving London & Surrounding Areas

We provide expert leak detection and roof maintenance throughout London, including:

• Central London

• North London – Enfield, Islington, Barnet

• South London – Croydon, Bromley, Wandsworth

• East London – Hackney, Tower Hamlets, Stratford

• West London – Ealing, Hammersmith, Hounslow

Frequently Asked Questions

Can small cracks cause roof leaks?

Yes. Even hairline cracks can allow water to seep into the roof structure over time, especially if combined with poor drainage or ageing materials.

How long should a flat roof last before leaking?

Properly installed and maintained flat roofs can last 20–30 years. Lack of maintenance or poor workmanship often shortens that lifespan significantly.

Are roof leaks covered by insurance?

Insurance may cover leaks caused by sudden damage, but neglect or lack of maintenance is rarely included. Regular inspection records strengthen your claim.

Need Help Identifying the Cause of a Leak?

If you suspect a leak in your flat roof, our London-based specialists can perform a full inspection using advanced detection methods. We identify the source quickly and recommend the most effective repair solution.