Why Does My Roof Leak Only in Heavy Rain or Wind-Driven Rain?
A roof that leaks only in heavy rain or wind-driven rain has a small weak spot that light rain never reaches. Hard rain, or rain pushed sideways by wind, can reach gaps at flashing edges, under the tile and around penetrations that stay dry the rest of the time.
That does not make it a minor problem. The gap is there all the time, and each storm lets in more water. The good news is that this kind of leak can be found, because it points to a short list of places.
Why light rain does not show it
Rain falling straight down lands on the surface and runs off. A gap has to be facing the water to take it in. In light rain, the water drains down the roof and never reaches the gap.
Heavy rain puts far more water on the roof at once. It can pile up at a valley or behind a chimney until it reaches a spot that is normally above the waterline. Wind pushes rain sideways and upslope, into places that face the wind and would never see water otherwise.
This is true for tile roofs in particular. Roof tiles overlap, but they do not seal. The underlayment beneath the tile is the second barrier, and its job is to keep wind-driven rain out of the house. In other words, the tile is the first layer and the underlayment is the second. When the second layer is worn, the first one is all you have.
Where these leaks usually hide
Flashing edges. Flashing at a chimney, a skylight or a wall is a sealed edge. If the seal has dried or pulled loose, water pushed against it in a storm can slip behind it. This is one of the most common causes of leaks that show up only in hard rain.
Pipe boots and other penetrations. A cracked boot may only leak when enough water runs down the pipe, which takes a strong rain. See our article on pipe boots and penetrations.
Cracked or slipped tiles. A tile that has moved can leave a gap that is open only on the side the wind comes from.
Aged underlayment. On older tile roofs, felt underlayment typically fails in about 20 years in our climate. Once it has cracked, water that gets past the tile can find its way through.
Valleys. A valley is where two roof planes meet and where monsoon water concentrates. It carries more water than any other part of the roof, so a small flaw there shows up first in a downpour.
What to notice when it leaks
Write these down while it is happening:
When did the water show up, and how long after the rain began? Was the wind blowing, and from which direction? Which room, and where in the room? Did it stop when the rain stopped?
A leak that appears only when wind blows from one direction points to the side of the house facing that wind.
How the cause is found
We start with those clues and work from the stain up the slope to the weak spots on that path. The method is the one we describe in how we find a roof leak: check the usual suspects, then use controlled water testing if the roof does not give the answer away.
Water testing is especially useful for this kind of leak. If a leak only happens in hard rain, waiting for a storm to find it is slow and unreliable. Putting water on one area at a time, while someone watches inside, shows which spot is the entry point.
Learn more about this service on our roof leak detection page.
What the repair looks like
The repair depends on what we find. A failed flashing edge is resealed or rebuilt. A worn pipe boot is replaced. A cracked or slipped tile is replaced or reset. If the underlayment under a section has failed, the tile in that area is lifted, the old felt is taken off, new underlayment and flashing go in, and your original tile is reset.
These are the repairs we describe on our roof repair page. If the underlayment has failed across the whole roof, we will tell you, and explain whether a tile lift-and-relay makes sense.
Do not wait for a bigger storm
A leak that only shows in the worst storms can seem safe to ignore. It is not. The gap is open every time it rains. Having the roof checked before the next hard storm is easier than dealing with a wet ceiling in the middle of one.
Frequently Asked Questions
Why does my roof leak only when the wind blows?
Wind pushes rain sideways and upslope into places that stay dry in straight-down rain, like flashing edges and gaps in tile laps.
Is a leak that only happens in big storms serious?
It can be. The gap is open in every rain. A hard storm just lets in enough water for you to see it.
Can you find it if it is not raining?
Often, yes. We check the usual suspects and can use controlled water testing to find the entry point on a dry day.
Do I need a new roof?
Usually not. These leaks tend to come from one spot. A new roof is only needed when the whole roof system has reached the end of its life.
Who do I call?
Call or text photos to (725) 502-3114.