Lead flashing does one of the most important jobs on a chimney stack while being one of the least thought about, sealing the junction where the stack passes through the roof covering. For homeowners in Keynsham, a flashing failure is one of the more common causes of a chimney leak, even on a stack where the brickwork itself looks perfectly sound from every angle. A flashing failure can be particularly frustrating for homeowners, since it often develops gradually and is well underway by the time any sign of a leak appears indoors.
Flashing forms a skirt of lead dressed into a mortar joint around the base of the stack, working alongside soakers, individual pieces of lead woven between the tiles or slates up each side of the chimney, and on the uphill side, a back gutter that channels rainwater safely around the stack rather than letting it pool against the brickwork below it. The quality of the original installation also plays a part, since flashing dressed in hurriedly or without enough overlap tends to fail earlier than a carefully finished job.
Over the years, lead can lift away from the brickwork as the mortar joint it is dressed into deteriorates, crack from age and repeated thermal expansion and contraction, or corrode thin after long exposure to weather. On many properties around Keynsham, this leadwork can be original to the house and, simply through age, is often overdue for renewal well before anything else on the roof needs attention. Properties that have had other roofing or building work carried out nearby can also see flashing disturbed inadvertently, which is worth mentioning to a contractor if recent work has taken place.
A useful clue that flashing is the culprit behind a leak is that water tends to appear during or after heavy or wind-driven rain rather than in light, steady drizzle, since it is often only under those conditions that water gets pushed under a lifted edge of lead. Bear in mind that the resulting damp patch inside the house is not necessarily directly below the chimney, since water can travel some distance along roof timbers before it finally drips through the ceiling.
A proper repair strips back the failed lead, prepares a clean mortar joint, and dresses new code lead in securely, rather than relying on mastic or sealant as a quick fix, both of which tend to fail again within a season or two of British weather. Done correctly, new flashing should comfortably outlast most other elements of the roof around it. A well-executed repair also tends to blend in visually with the surrounding roofline, rather than looking like an obvious later addition.
If you suspect a leak near a chimney on your Keynsham property, it is worth having the flashing checked rather than assuming the worst about the brickwork. Brunel Roofing Bristol offer free inspections and can carry out lasting lead flashing repairs, backed by a 15-year guarantee.
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