Roof leaks only when it is windy
Rain that falls straight down runs over a roof. Rain driven sideways by wind is pushed up under the edges of shingles, into the seams of flashing and through vents that face the weather. A leak that appears only in stormy weather is almost always at one of those details, and it is real even though a calm rainy day never shows it.
The symptom
What you are seeing
- Weeks of ordinary rain pass without a mark. Then a storm comes in off the bay with a strong wind behind it and by morning there is a wet patch on a ceiling, a drip in the attic or water on a windowsill below a wall where the roof meets the house. When the wind drops, the leak stops, even if the rain continues. It can be years between storms that line up the right way, which is why these leaks are so often dismissed.
- Note the wind direction on the night it happened, and which side of the house the mark is on. Wind-driven leaks nearly always come from the weather side. Then look at that slope for the details that face the wind: the exposed edges of a rake, a ridge or hip cap, a wall that rises above the roof, a vent turned toward the weather or a skylight. A leak here is not a sign the roof is worn out; it is a sign one detail was not built for sideways rain.
Most likely first
Likely causes
Rain pushed under the shingle laps
Wind lifts the edge of a shingle a fraction and drives water up beneath it, past the point where the next course overlaps. On low-pitched slopes and at eaves without a sealed starter course, that water reaches the underlayment.
Ridge and hip caps facing the weather
The caps along the top of a roof are the most exposed pieces on it. Ridge vents in particular can take water straight in when the wind is on them, and a cap that has lifted or lost its fastener lets rain under.
Flashing laps open on the windward side
Step flashing along a wall and the laps around a chimney shed water that runs down. Water blown sideways finds the open end of each lap. A counter flashing that has pulled out of its mortar joint leaks in exactly this weather and no other.
Vents, pipes and turbines turned to the wind
A roof vent or a pipe boot with its opening or its weak seam toward the weather takes rain in every time the wind is from that quarter. It stays dry from every other direction.
Rake edges without a drip edge
The sloping edge of a gable is where a crosswind hits first. Without a metal drip edge under the roofing there, water is blown back under the covering and along the sheathing.
The honest rule
Repair or replace
A wind-driven leak on a roof in otherwise good condition is a repair, and a specific one: the detail that faces the weather is rebuilt to shed sideways water, with sealed laps, a drip edge, a storm collar on the pipe or a vent that closes against the wind. We want to show you which detail and why, because the general condition of the roof does not explain a leak that only happens in a gale.
It becomes a replacement question when the covering has aged to the point that the laps no longer seal at all, when the shingles have lost their bond and lift in any breeze or when the underlayment has been wet enough times to have failed across the slope. Then every storm from that quarter will find a new way in, and repairing them one at a time is a poor use of money. Between those two, a roof with sound covering and a handful of weak details on the windward side can be brought right with a day of flashing work and a season of proof.
What fixes it
The service for this, and where to read more
Service
Roof leak repair
We trace where rain gets into the roof and explain the repair needed at its source.
Service
Roof inspections
A roof assessment with photographs, a written report and a clear explanation of what needs attention.
Guide
Roof repair or replacement
A repair is worth considering when the damage is limited and the surrounding roof is in good condition.
Related problem
Ceiling stain that appears after rain
A stain that darkens or spreads after rain means water is getting through the roof and reaching the drywall.
Related problem
Cracked or slipped roof tiles
A cracked, chipped or slipped tile is common on a concrete or clay roof and rarely a leak on its own, because the underlayment beneath it is what keeps water out.
Questions
Asked about this problem
The roofer says the roof is fine. Why does it still leak in storms?
Because a roof can be in good condition and still have one detail that fails sideways. An inspection on a dry day looks for wear, and a wind-driven leak is not wear. Ask for the windward details to be checked one at a time, and tell them which storms cause it, including the wind direction. That narrows the search to a few square feet.
Can a hose test find a wind-driven leak?
Sometimes, if the water is aimed up the slope at the suspect detail rather than run down over it, to imitate the wind. It takes someone inside watching and someone on the roof working from the bottom up. It is slow but it is the surest way to prove which lap is the one.
Is it worth fixing if it only leaks once or twice a winter?
Yes. Each time, the sheathing and the insulation get wet and dry slowly, and the damage builds up between the leaks you notice. A leak that shows twice a winter has probably wet the roof deck a dozen more times without reaching the ceiling.
Free estimate
Find out what it costs
Tell us what's happening at your property, one step at a time. We'll review your request during business hours and arrange a free inspection.
What happens after you send it
- We call during business hours to set a time.
- A free visit. We measure on site and nothing is signed at the door.
- The proposed work and the price, in writing.
- (925) 555-0100Phone
- Mon–Fri 7:00 AM – 5:00 PMHours
Sat by appointment · Sun closed
100 Example Road, Brentwood, CA 94513 · office@example-roofing.demo
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