Common Causes of Roof Leaks and Water Damage

Roof leaks rarely come from nowhere. There’s usually a specific, identifiable cause. Here are the most common ones we come across.

Aged or perished waterproofing membranes

Waterproofing membranes have a working life, and once they pass it, cracking and general breakdown become far more likely. This is one of the most common causes of leaks on flat or low-pitch roofs.

Flashing that has lifted or failed

Flashings around parapets, chimneys, and roof penetrations are common weak points. Once a flashing lifts even slightly, water can get behind it during rain.

Ponding water on flat roofs

Water that doesn’t drain away properly sits on the roof surface for longer, putting sustained pressure on any weak point in the waterproofing. Blocked or poorly positioned outlets are a common cause.

Cracks from movement or age

Buildings move slightly over time, and that movement can crack a waterproofing layer that was previously sound. This is one reason a system that worked for years can suddenly start leaking.

Damage from other building work

Roof penetrations added for aerials, solar panels, or other fittings, if not properly sealed, can become a new entry point for water.

What to do about it

Because leaks can originate some distance from where the water shows up inside, an on-site assessment is the most reliable way to find the actual source. See our roof waterproofing page for more, or if the roof has been repaired before and is leaking again, our waterproofing repairs page.

FAQ

Can a roof leak from a spot that looks fine?
Yes. Water often travels along a structure before showing up as a stain, so the visible damage isn’t always directly below the entry point.

Do all roof leaks need the whole roof re-waterproofed?
No. Many leaks can be addressed by repairing the specific failed area, depending on the assessment.