Common Causes of Flat Roof Leaks

Flat roofs are more susceptible to leaks than pitched roofs because water cannot run off as quickly. However, most leaks are preventable with proper maintenance and timely repairs. Here are the most common causes.

Ponding Water

Water that pools on a flat roof exerts constant pressure on the membrane and accelerates deterioration. This is usually caused by inadequate falls (the slight slope built into every flat roof to direct water to drains) or blocked drains and outlets.

Faulty or Deteriorated Flashing

Flashing is the material used to seal the junction between the roof membrane and walls, chimneys, skylights, and upstands. When flashing lifts, corrodes, or cracks, water can penetrate behind it. This is one of the most common causes of flat roof leaks.

Membrane Damage

• Blistering and bubbling caused by trapped moisture or air
• Cracks and splits from UV exposure or temperature movement
• Punctures from foot traffic or debris
• Seam failures in older felt or built-up roofing systems

Blocked Drains and Gutters

Leaves, moss, and debris can block roof drains and gutters, causing water to back up and pond. Regular clearing — especially in autumn — is one of the simplest things you can do to protect your flat roof.

Poor Original Installation

Many leaks we investigate can be traced back to shortcuts taken during installation. This includes insufficient membrane overlaps, poorly bonded seams, or inadequate upstands at the roof edges. Always use a qualified, experienced roofer.

If your flat roof is leaking, don't delay. Contact us for a fast response and diagnosis.