Because wind-driven rain is pushed sideways and upwards, not just downwards. In ordinary rain, water runs down the tiles and off into the gutter. In a storm it is driven under tile laps, past a loose verge, through a gap in flashing, or over the top of a ridge whose mortar has gone. The defect is there all the time — only the storm has enough force to exploit it.
- A storm-only leak is not a minor leak. It is a defect that happens to need wind to show itself.
- Wind direction matters: if it leaks on a south-westerly and not an easterly, that tells you which elevation to look at.
- Water can be driven uphill under tile laps. Gravity is not the only force involved.
- The entry point is usually higher up and to one side of where the water appears inside.
What changes when the wind gets up
A pitched roof is not a sealed surface. It is an overlapping arrangement of tiles or slates designed so that water running downhill passes from one to the next and off the bottom edge. The whole system assumes water is moving down.
Driving rain breaks that assumption. Wind pushes water horizontally and can force it up the underside of a tile lap, past the point where the overlap would normally protect. On an exposed elevation in a strong wind, the pressure difference across the roof covering can literally pull water through gaps rather than relying on it finding its own way.
So a roof that is perfectly watertight in a steady November drizzle can let water in during twenty minutes of a south-westerly gale. Nothing has changed about the roof. The loading has changed.
The usual suspects on a storm-only leak
| Defect | Why it only shows in heavy rain | Typical fix |
|---|---|---|
| Cracked or slipped tile | Normal rain runs over the gap; driven rain goes through it | Replace the tile and check the fixings nearby |
| Perished ridge mortar | An open ridge line takes water only when wind drives it in | Re-bed and mechanically fix the ridge |
| Loose or missing verge pointing | The gable edge takes the wind first | Repoint, or fit a dry verge system |
| Split or lifted flashing | Needs pressure to push water past the lap | Replace the lead properly, not with mastic |
| Blocked or overflowing valley | Only backs up when the volume is high | Clear, then check the valley lining |
| Perished underlay at the eaves | Water blown back under the tiles finds the tear | Eaves repair, or re-roof if widespread |
| Undersized or blocked gutters | Overflows only in heavy volume, soaking the wall | Clear, resize or add a downpipe |
| Chimney flashing or flaunching | Driven rain hits the stack from the side | Repoint, re-flaunch, renew flashings |
Note how many of these are detailing rather than the tiles themselves. A roof covering in good condition can still leak badly if the ridge, verge and flashings have gone.
Wind direction is a diagnostic tool
This is the most useful thing you can do yourself, and it costs nothing.
Next time it leaks, note which way the wind was blowing. If the leak appears on a south-westerly — the prevailing direction in the Midlands — and not on an easterly, the defect is almost certainly on the south-west-facing side of the roof, or on a feature exposed to it.
Keep a note over a few storms and the pattern narrows the search dramatically. It is genuinely common for a roofer to be shown a damp patch on a north-facing bedroom ceiling when the actual entry point is a cracked tile on the opposite slope, with the water tracking across the roof structure in between.
It also helps distinguish a roof leak from a wall problem. Driving rain on a solid wall can soak through the masonry and show inside with no roof involvement at all, and that leak will also be storm-correlated. The difference is usually where it appears: ceiling and high on the wall points at the roof, a patch in the middle of a wall points at the wall.
Why the damp patch is not under the hole
Water entering a roof rarely drops straight down. It lands on the underlay, runs along it until it meets a batten, travels sideways along the batten, and only then finds a nail hole, a tear or the end of a run and drops through.
On a typical roof the entry point can be several metres away from where the stain appears, and usually higher. It also means the ceiling stain marks the end of the journey, not the beginning, so repairs aimed at the spot directly above it frequently fix nothing.
The way to find it is to get into the loft during or just after heavy rain with a torch, and look for the actual water path: wet trails on rafters, drips forming on the underside of the underlay, staining that is fresh and dark rather than old and dry. That evidence is worth far more than any amount of looking at the roof from the garden.
What to do during the storm, safely
- Contain it. A bucket, and if water is pooling above a ceiling, a small hole drilled in the bulge to let it drain in a controlled way — a collapsing ceiling is worse than a hole.
- Move what matters out of the way and lift anything stored in the loft off the floor.
- Photograph everything, including the date and the weather. If this becomes an insurance claim, that evidence is what gets asked for.
- Go into the loft with a torch while it is still raining and look for the water path. This is the best diagnostic opportunity you will get.
- Do not go onto the roof. Not in a storm, not afterwards on a wet roof, and not on a ladder in wind. This is where people get seriously hurt.
Is it worth fixing if it only happens twice a year?
Yes, and the reason is what the water is doing between the times you notice it.
Every time water enters, it wets timber. Battens, rafters and ceiling joists that are repeatedly wetted and then dried do not simply return to normal; they develop rot over time, and the roof covering loses its fixings as nails corrode in damp timber. Insulation that gets wet compacts and stops insulating. Plaster degrades. None of this is visible from the room below until it is advanced.
There is also a straightforward cost argument. A slipped tile or a section of ridge re-bedded is a modest repair. The same defect left for five winters becomes timber repair, insulation replacement and a ceiling — and quite possibly a bigger roof job, because by then the nails and the underlay have had five more years of being wet.
What repairs typically cost
These are the roofing figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Minor roof repair | from £150–£400 | Slipped or broken tiles, usually one day |
| Chimney repointing / flashing | £300–£900 | Access dependent |
| Flat roof (EPDM / GRP) | £80–£120 per m² | Warm or cold deck |
| Full re-roof (typical semi) | £5,000–£9,000 | Strip, membrane, batten, re-tile |
| Larger / detached re-roof | £9,000–£12,000+ | Scaffolding included |
Most storm-only leaks turn out to be at the lower end — a tile, a section of ridge, a flashing. The expensive outcomes are the ones that were left long enough to involve the timber.
We trace it from inside the loft as well as on the roof, because the entry point is rarely above the stain. Free inspection, fixed written quote.
Frequently asked questions
Can wind really push water uphill under tiles?
Yes. Driving rain carries horizontal momentum, and the pressure difference across a roof covering in a strong wind can move water against gravity for a short distance. It is exactly why tile laps are specified by pitch and exposure, and why a roof that is fine in steady rain can let water in during a gale.
Why does my roof leak in heavy rain but not light rain?
Because the defect needs force or volume to exploit. A small gap that ordinary rain simply runs past will take water when it is driven sideways into it, and a gutter or valley that copes with drizzle will back up and overflow in a downpour. The fault is present either way; the weather decides whether it shows.
Could it be condensation rather than a leak?
Possibly, and it is worth ruling out. Condensation is widespread rather than localised, worse in cold weather, often shows as droplets across the underside of the underlay, and does not correlate with rain. A leak is localised, follows the weather and leaves a defined stain with a tide line.
How do roofers find a leak that only happens in storms?
By inspecting the loft for the water path, examining the elevation facing the prevailing weather, checking every detail — ridge, verge, valleys, flashings — rather than only the tiles, and using what you can tell them about wind direction. Where it remains elusive, controlled hose testing of one area at a time can reproduce it.
Should I claim on insurance for a storm leak?
It depends on the cause. Sudden storm damage is generally covered; gradual wear, perished mortar and failed flashings generally are not, because insurers treat those as maintenance. Photograph everything, keep the dates and get an itemised written quote. An insurer will usually want evidence that the damage was caused by a specific event.
Is it safe to go up and look myself?
No, and this is the one piece of advice worth taking literally. Wet roofs are lethally slippery, ladders in wind are unstable, and roof coverings can give way underfoot. Inspect from inside the loft and from the ground with binoculars. Anything that needs eyes on the covering itself needs someone equipped for working at height.
Find the defect before the timber pays for it
We inspect from the loft as well as the roof, work with the wind direction you have observed, and tell you plainly what is a repair and what is not. Free inspection, fixed written quote.