Why Does My Roof Only Leak in Heavy Rain?
Wind-driven rain, overloaded valleys and storm-side flashing. Why some leaks only show in downpours, and how to find them.
Why does my roof only leak in heavy rain? Usually because storm wind drives rain sideways or uphill under shingle edges, flashing and tile laps that stay dry in gentle rain, or because valleys and gutters overflow faster than they drain. The weak spot is often on the side facing the storm. We find these with targeted hose tests as part of our roof leak repair in Valrico, FL.
Five reasons a roof leaks only in heavy rain
- Wind-driven rain.Valrico's summer storms come in with gusts that push water under laps and flashing. Normal rain runs straight down.
- Overloaded valleys.Two slopes dump into one channel. In a downpour, debris-clogged valleys overflow under the shingles or tiles.
- Clogged gutters.Water backs up over the edge and under the first course, into the fascia and decking.
- Flashing on the storm side.Wall, chimney or skylight flashing that only takes water when rain is driven straight at it.
- Tile laps and worn underlayment.On tile roofs, heavy rain gets past the tiles in volume and finds every crack in old felt.
Valrico's rainy season makes it worse
From June through September, sea-breeze thunderstorms build most afternoons. About two-thirds of Tampa Bay's yearly rain falls in those four months, and 2024 was the wettest rainy season on record. A weak spot that stays dry all winter can leak every day in August.
What to note before you call
- Which way the wind was blowing when it leaked
- Whether it leaks in every heavy rain, or only some
- How long after the rain started the drip appeared
- Where inside it shows, and roughly where that is on the roof
These answers cut the time it takes to find the leak. The stain is usually not under the hole: see water stain on ceiling: where is the leak really?
How we find it
We check the storm-facing slope first: flashing, valleys, pipe boots and edges. Then we run a hose test in the same direction the wind blew, one section at a time, with someone in the attic. More in roof leak detection. If your answer to "why does my roof only leak in heavy rain" turns out to be flashing, see roof flashing repair.
Heavy rain leak questions
Why does my roof only leak in heavy rain?
Heavy rain usually comes with wind, which pushes water sideways or uphill under shingle edges, flashing and tile laps. It also overloads valleys and gutters. Gentle rain just runs off.
Why does my roof leak only when the wind blows one way?
The weak spot is on the side facing that wind. Flashing, pipe boots or laps on that slope only take water when rain is driven straight at them.
Can clogged gutters cause a roof leak?
Yes. When gutters back up in a downpour, water rises over the roof edge and under the first course of shingles, rotting the fascia and decking.
Is a leak that only happens sometimes still urgent?
Yes. Each time it leaks, the decking, insulation and drywall get wet again. In Florida humidity, that leads to rot and mould.
How do you find a leak that only happens in storms?
A hose test that copies the storm: water aimed at one section at a time, in the same direction the wind was blowing, with someone watching in the attic.
Leak that only shows in storms?
Call (813) 555-0147 or text us a photo of the stain. We'll find where the water is getting in, show you, and give you a written price.