If your roof only leaks when it rains heavily — but stays dry in light rain — that pattern is actually a useful clue. It tells us the leak has a specific entry point that only the volume of a downpour reaches. Light rain runs off without finding it; heavy rain forces water through. This article explains the most common causes and why a proper inspection matters.
Broken or slipped tiles
A cracked or slipped tile leaves a gap in the covering. Light rain may run off the surrounding tiles without reaching it, but heavy rain — especially wind-driven — forces water through the gap and onto the underlay. If the underlay is also torn or degraded, the water reaches the timbers and ceiling. See our roof repairs page.
Failed lead flashing
Lead flashing seals the joins between the roof and chimneys, walls and valleys. A crack or split in the flashing is invisible in light rain, but heavy rain drives water straight through it. Failed flashing around chimneys is one of the most common causes of heavy-rain leaks. See our leadwork page and chimney repairs page.
Chimney defects
Chimneys are fully exposed above the roofline. Cracked flaunching around the pots, weathered mortar joints and failed flashing all let heavy rain in — often some distance from where the damp appears inside. Read our article on common chimney leaks during winter.
Valley leaks
A valley carries a large volume of water where two roof slopes meet. In heavy rain that volume is at its highest, so any crack in the valley lining, slipped tiles beside it, or debris choking the channel causes water to overtop and leak. See our roof valleys page.
Flat roof splits
Flat roofs leak through splits, blisters and failed seams that light rain does not reach but heavy rain forces water into. Ponding water worsens the problem. See our flat roofing page.
Tracing the source
Because water travels before it shows, the damp patch is rarely below the entry point. We use a drone to inspect the roof close up and trace the true source of a heavy-rain leak. Arrange an inspection through our roof leak repairs page or quote form.
Frequently asked questions
Why does my roof only leak during heavy rain?
A roof that leaks only during heavy rain has a specific defect that the volume of a downpour exposes — a broken or slipped tile, a crack in the lead flashing, a failed valley, or a flat roof split. Light rain runs off without reaching it. We inspect the roof to find and fix the exact cause.
Can you find a heavy-rain leak with a drone?
Yes. A drone survey gives clear close-up imagery of tiles, flashing, chimneys and valleys, which often reveals the source of a heavy-rain leak without scaffolding. Where the cause is hidden inside the structure, we may recommend a closer physical inspection.