Detecting Common Flat Roofing Problems

Worn flat roof surface with visible ageing and weathering, adjacent to a pitched tiled roof and skylight — example of a roof in need of repair or replacement.

Flat roofs are a practical and modern roofing solution, but their design makes them vulnerable to specific issues that can lead to leaks, structural damage, and costly repairs. Knowing what to look for can save you time, money, and hassle in the long run. Here's how to spot the warning signs before they become major problems.

1. Pooling Water

Flat roof with visible moss and weathering on a residential extension, showing early signs of deterioration — Armstrong Roofing inspection in progress.

One of the most common issues with flat roofs is water pooling. If your roof doesn't drain properly, standing water can degrade materials and eventually lead to leaks.

Signs to watch for:

  • Visible puddles after rain
  • Stains or discoloration from water buildup
  • Sagging areas in the roof surface


2. Cracks, Blisters, and Splits

Flat roofs often use membrane materials that can crack, blister, or split due to temperature changes and UV exposure.

What to check:

  • Bubbling or blistering on the surface
  • Visible rips or splits in the roofing material
  • Cracking around seams or edges

3. Loose or Damaged Flashing

Flashing protects the edges and joints of your roof. When it's loose, water can easily get inside.

Inspect for:

  • Gaps or peeling at edges, skylights, or vents
  • Rusted or missing flashing components


4. Moss and Algae Growth

Moss isn’t just an eyesore — it holds moisture against your roof, encouraging rot and decay.

What it means:

  • A sign your roof is retaining too much moisture
  • Often indicates poor drainage or aging materials


5. Interior Signs of Roof Trouble

Not all problems show up outside. The inside of your home can provide early clues.

Look out for:

  • Water stains on ceilings or walls
  • Peeling paint or damp patches
  • A musty smell indicating mold or mildew


6. Membrane Shrinkage or Lifting

Over time, the roofing membrane can shrink, especially around penetrations like vents and pipes. This leaves parts of the roof exposed.

Warning signs:

  • Pulling or lifting around fixtures
  • Exposed insulation or underlayment

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