Why does my roof leak when it is windy?

A lead upstand, a verge or a lap is designed to shed water running downwards. Rain arriving at an angle, with pressure behind it, can travel upwards under a lap or behind an upstand for a surprising distance. Nothing needs to be visibly broken for this to happen.

Because it depends on angle, the leak often occurs only with wind from one direction, which immediately narrows the search to one or two elevations.

Verges and gable details take the most punishment on an exposed elevation. Chimney flashings, particularly the back gutter behind a stack, are next. Roof lights, dry-fix components at ridges, and coverings that have lifted slightly under uplift complete the usual list.

Wind can also drive water into a roof space through ventilation openings without any defect at all, which is worth ruling out before work is specified.

Write down the date, the approximate wind direction and how heavy the rain was each time it happens. Two or three of those observations are often enough to point diagnosis at a single elevation, which saves both time and access cost.

A visual survey then examines those details closely, and physical access confirms anything the images can only suggest.

Before assuming a junction detail is at fault, check whether the pattern could instead be explained by a blocked gutter overflowing onto a wall below, or by rain being funnelled off a taller neighbouring roof onto an exposed section of your own. Both can look identical to wind-driven ingress from inside the house.

It is also worth checking whether the same wall has a render or pointing defect that lets water track down brickwork and appear at a similar point internally, since that has nothing to do with the roof at all.

A visual inspection of the exposed elevation, cross-referenced against the wind directions you have logged, usually identifies the candidate detail quickly. Where the finding is not conclusive from the outside, a controlled hosing test aimed from the recorded direction can reproduce the leak under observation, which is far more reliable than waiting for the next storm.

That test only works once the likely area has been narrowed down, which is why the observation stage matters as much as the visit itself. Where more than one elevation is exposed to prevailing weather, testing them one at a time, rather than all at once, keeps the result unambiguous.