Why your tiled roof only leaks in heavy rain

The leak isn't where the stain is

One of the most confusing things about a tiled roof is that a water stain on your ceiling almost never sits directly under the spot where water got in. Tiles shed water by overlapping and relying on gravity. When water does sneak past them, it runs along the rafters, battens and insulation before finally dripping — often metres away from the real entry point.

That's why patching the ceiling, or guessing at the tile above the stain, so often fails. The water just finds the same path again the next time it rains.

How wind-driven rain gets in

Mackay's storms don't bring gentle, vertical rain. During cyclones and heavy summer downpours, high winds push rain sideways. That horizontal force drives water up and underneath the tile overlaps — past the line of defence the roof relies on in normal weather.

Once water is under the tiles, it's inside the roof. From there it follows the timber framing until it reaches a low point and starts to drip. So a leak that only ever appears in a big storm is a classic sign of wind-driven rain ingress, not a single obviously broken tile.

What to look for

• Stains that appear or grow only during storms, then seem to dry out
• Damp patches that move or spread across the ceiling over time
• Water marks some distance from the nearest external wall or valley
• Multiple small marks rather than one obvious drip point

How a specialist finds it

Because the entry point and the stain are in different places, tracing a storm leak takes a methodical approach — reading the roof's layout, checking the valleys, flashings and tile overlaps, and working back to where water is most likely getting under the tiles. Getting the diagnosis right is what separates a lasting repair from another patch.