24 July 2026

Did you know frost makes small roof defects bigger every year?

Water that freezes expands — and pries every crack and gap further open. Why roof leaks surface in winter of all seasons, and what to do before then.

The mechanism is simple physics: water that freezes expands. Rainwater finds every hairline crack and gap in your roof, freezes there on a cold night and pries the opening a little further apart. During the thaw, new water runs in, and the next frosty night the game repeats. That is how a hairline crack from autumn grows into a leaking gap within a single winter.

Each material takes its own share. Porous roof tiles and ridge tiles absorb water and crumble with frost; mortar joints disintegrate. On a flat roof, standing water is the biggest culprit: with a blocked outlet, a puddle remains that freezes and works the seams of the covering open. And melting snow then finds every opening — snow thaws slowly and presses water against the roof for days, far longer than a rain shower.

That is why roof leaks so often surface in winter of all seasons: the autumn storms create the defects, the frost enlarges them, and the thaw that follows is the classic leak moment. One nuance: drips under a roof window in cold, dry weather are usually condensation, not a leak.

What you can do, you do before winter: have small defects repaired at a planned moment, ideally during the autumn check, and keep gutters and outlets clean so no water keeps standing. Never step onto a frosted or snow-covered roof and don't go chipping ice yourself. If it does leak in the middle of winter, that is an emergency repair of € 150-450; frost-opened seams on a flat roof are a repair of € 175-600. All guide prices are in the price index.