Can damaged flashing cause a roof leak?

Lead moves with temperature. Over-long pieces, poor fixing or thin material lead to fatigue cracking along a line. Wedges and clips release, allowing an upstand to lift. Where a chase in masonry has never been repointed, the whole edge gradually opens.

Substitutes fail faster. Mortar fillets crack because mortar cannot flex; sealant and flashing tape have short lives when exposed to weather and movement.

Water passing a flashing is behind the covering and above the underlay. From there it runs downslope or along a lap until it finds a hole, a nail or a lap end. The internal stain can be a metre or more from the flashing, and on the other side of a room from the wall the flashing serves.

This is why a repair aimed at the stain rather than the junction so often fails.

Correctly sized pieces with adequate laps, proper dressing to the profile of the covering, secure clips and wedges, and a repointed chase. Done properly, leadwork is long-lived; done as a patch, it is a repeat visit.

Ask what the failure was, what material and detail will replace it, and whether adjacent lengths are in the same condition.

From ground level, look for lead that has visibly lifted away from a wall, a colour change suggesting corrosion, or a line of green staining running down brickwork below a joint, which often indicates water has been running over the flashing rather than being carried away by it. None of these confirm a leak on their own, but any of them is reason enough to have the detail looked at.

Where render or pointing has recently been redone above a flashing without the lead being lifted and reset, ask whether the flashing itself was inspected at the same time, since resealing around a failing flashing without addressing it is a common way for the same fault to resurface.

A flashing that is letting in water steadily should not wait for a routine maintenance visit, but nor does it usually need emergency attendance unless water is entering fast or reaching electrics. Arranging a prompt, planned repair strikes the right balance between cost and risk for most cases of this kind.

Where scaffolding or a tower is already being used for other work nearby, it is worth checking whether flashing repairs can be included at the same time, since access is often the larger part of the overall cost.