TL;DR
A roof that only leaks in heavy rain usually doesn’t have a hole. It has a drainage or wind problem: valleys and gutters back up, or wind pushes water sideways past laps built to shed water flowing downhill. The two most common local causes are spring debris packing the drainage and rubber pipe boots split by our sun. Patching under the ceiling stain rarely fixes it.
A roof that leaks in heavy rain and stays perfectly dry the rest of the year is telling you something specific. It usually doesn’t have a hole in it. If it did, you’d see a stain after every shower.
What you almost certainly have is a capacity problem. The roof sheds water fine at normal volume, then something upstream backs up, overflows, or gets pushed sideways by wind, and water gets in through a joint that works exactly as designed in ordinary rain.
That distinction matters, because the two problems get fixed differently. A hole gets patched. A capacity problem gets traced back to drainage, and patching the spot where water appears does nothing at all.
Here’s how to tell which one you’ve got, what causes it on roofs around here, and what a real fix looks like.
Why does a roof only leak in heavy rain?
Because heavy rain does three things ordinary rain doesn’t. It delivers more water than your drainage can carry, so valleys and gutters back up and push water under shingles. It arrives at an angle, so wind drives it sideways past laps built to shed water flowing downhill. And it keeps going long enough to soak through a seal that would have dried out in a shower.
Every roof is built on one assumption: water flows downhill, and each layer overlaps the one below it. That assumption holds beautifully until water stops flowing downhill. Wind driven rain moves sideways and even upward under a shingle edge. Ponded water sits still and finds its way through by pressure and time.
So the leak isn’t a failure of the roof surface. It’s a failure of the conditions the roof surface was designed for.
What actually causes it
Angi lists seven common causes of roof leaks in heavy rain, and they sort neatly into the three mechanisms above: worn or missing shingles, failing flashing, skylight seals, clogged gutters, vent leaks, loose fasteners on metal roofs, and penetrations from solar panels.
Two of those dominate on local roofs, and both are climate driven.
The first is drainage. Spring drops a heavy load of oak pollen and leaves right as storm season starts, and it packs into gutters and valleys. Water that can’t drain backs up onto the roof and gets under the shingle courses. That roof didn’t fail. Its drainage did.
The second is sun damaged seals. Rubber pipe boots dry out and split in our sun, and they’re the most common leak source we find. Heat and UV also bake the sealant around flashing until it cracks. A split boot or a lifted flashing edge will shed a light shower and pass water the moment rain is heavy or driven.
Angi also notes that architectural shingles last about 20 to 25 years. If yours are near that and the leak is new, age is a live suspect rather than a single failed part.
A real example of a capacity problem
On a roof and gutter repair we completed in 78254 out near Alamo Ranch, the fix had two halves and only one of them was roofing.
The crew took the damaged roofing down to the deck, confirmed the surface underneath was solid, swapped decking where it needed it, and ran new ice and water barrier into the valleys before matching the existing roof with Owens Corning Supreme shingles in Driftwood.
Then the actual cause. The front downspout wasn’t draining right. So they closed off that hole, resloped the gutter, and moved the downspout to the opposite end where the water actually needed to go.
That’s the whole lesson in one job. You could have replaced every shingle on that elevation and the water would still have backed up in a downpour, because the water had nowhere to go. Little corrections like that are what keep water off the fascia and away from the house.
How do you find a leak that only shows up in a downpour?
Look during the rain, not after it. Get into the attic with a flashlight while it’s actively pouring and trace the water uphill from where it drips. Water runs along the underside of the deck or a rafter before it falls, so the wet spot on your ceiling is almost never under the entry point.
This is the single most common reason a repair doesn’t hold. Somebody patches directly above the ceiling stain, seals a section of perfectly good roof, and misses the real entry point entirely. Our guide on how to detect roof leaks in the attic walks the process.
If you can’t get up there safely during a storm, note exactly when it leaks. A leak that only appears when rain comes from one direction points at wind driven water on that elevation. A leak that shows up ten or fifteen minutes into a hard rain, then stops soon after, points at drainage backing up and then clearing.
Those two patterns send a roofer to completely different parts of the roof, so the detail is worth writing down.
Is it urgent if it only leaks sometimes?
Treat it as urgent. An intermittent leak is still wetting decking and insulation every time it rains, and the damage accumulates whether or not you can see it. The gap between the first stain and real structural damage is measured in seasons, not years.
The reason people wait is that the ceiling dries out between storms and the problem looks like it went away. It didn’t. The wood above the drywall stayed damp longer than the paint did, and insulation that gets wet repeatedly stops insulating.
If water is coming in right now, a small active leak is still an emergency, and we respond to leak calls within 24 hours.
What a proper fix looks like
Diagnose first, and expect the fix to include drainage. On a volume driven leak the repair usually touches three things: whatever is blocking or misrouting water, the joint that let water in, and any decking that got soft while the leak went unnoticed.
A quality repair also replaces the failed component rather than sealing over it. New flashing instead of reused, a new pipe boot instead of a bead of caulk around a split one. Reused parts are one of the top reasons a roof still leaks after a repair.
Then get ahead of it. Most volume driven leaks are a maintenance miss rather than bad luck, and the routine in our guide to preventing roof leaks catches the boots, the flashing, and the drainage before the weather exploits them.
What to do next
Three things worth remembering. A roof that only leaks in heavy rain usually has a drainage or wind problem, not a hole, so patching the spot under the stain tends to fail. The two most common local causes are valleys and gutters packed with spring debris and rubber pipe boots split by our sun. And intermittent is not the same as minor, because the decking gets wet every single time.
If your ceiling stains only after a hard rain, get it looked at before the next one. Our free 27-point roof inspection comes with photos and a written report, and it’s built to find drainage and seal failures while they’re still a repair. Call (210) 267-9029 or schedule a roof repair inspection.
