Failing lead flashings are one of the most common causes of roof leaks - Cambridge Roofers cut and dress lead correctly so the repair lasts.
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Lead flashings are the strips and soakers that seal the joints between your roof covering and any vertical surface - chimney stacks, dormer cheeks, parapet walls, and flat roof abutments. When they fail, rainwater tracks silently into the roof structure, often for months before a stain appears on a ceiling. By then, the timber beneath may already be softened.
Poorly fitted or deteriorated lead is one of the most frequent reasons homeowners find water inside their property. The problem is not always dramatic. It can be a slow drip that only shows after heavy or prolonged rain, or a damp patch on a chimney breast that gets written off as condensation.
You do not need to climb onto the roof to spot trouble early. From the ground or an upstairs window, look for these indicators:
Any one of these is worth investigating. Two or more together points strongly to a lead flashing problem that will not resolve itself.
Lead moves. It expands in warm weather and contracts in the cold, and over years this thermal cycling causes fatigue in the metal, particularly at bends and drips. A correctly installed flashing is dressed in short sections - typically no longer than 1.5 metres - with expansion joints built in. When flashings are installed in single long runs, or are fixed too rigidly, cracking at the folds is almost inevitable.
A common problem is that original lead was laid to an insufficient Code thickness. Lead sheet is specified by Code number - the higher the Code, the thicker the sheet. Code 3 (1.32 mm) is the minimum for soakers between slates or tiles. Code 4 (1.80 mm) and Code 5 (2.24 mm) are used for chimney flashings and flat roof upstands. Thin lead in a location that demands something heavier simply will not survive normal weather over the long term.
Mortar failure is another factor. Step and cover flashings are tucked into a raked mortar joint and held with a wedge of lead or mortar. Once that joint opens - whether from age, frost damage or settlement - the flashing is no longer fixed at the top, and water finds its way behind it immediately.
Bodged repairs with mastic, self-adhesive flashing tape or roofing felt are also worth noting. These materials degrade faster than lead, and they are often applied over an underlying problem rather than to solve it. A flashing that has been patched with tape may look watertight but still allow water to track through at the edges.
Not every lead problem needs a full replacement. If the lead itself is in sound condition but the mortar joint has opened or the wedges have dropped, repointing and re-wedging can restore a watertight seal. If the lead has cracked, thinned through corrosion, or was installed to the wrong Code in the first place, replacement is the correct answer.
Asking a roofer to patch lead that is already fatigued will cost money twice - once for the patch and once for the replacement that will follow within a few years. A straight assessment of whether the existing lead is serviceable or not is the most useful thing any roofer can offer at the inspection stage.
Chimneys are the most demanding location for lead work. A full chimney flashing set includes back gutters, side soakers, step flashings and a cover flashing - each element must overlap and discharge correctly so water cannot pond or back up. The back gutter behind the chimney is often the first to fail because it carries the most water and is the hardest to inspect.
Dormers typically have lead soakers under the side tiles and a lead apron at the base. On older properties the lead may have been installed without adequate expansion allowance, leading to splits at the corners.
Flat roof abutments - where a felt or EPDM rubber flat roof meets a wall - should have a lead flashing dressed into the wall above the upstand. If this flashing has dropped or the mortar joint has failed, water gets in at the top of the upstand rather than being directed away from it.
Correct lead work means cutting the sheet to the right profile, dressing it with a bossing mallet or dresser to achieve a clean fold without thinning the metal, and fixing it to the correct Code for the location and pitch. Wedges are hammered into the raked joint, the lead is turned in, and the joint is pointed with an appropriate mortar or lead-based sealant. A tingle or clip is used to support the free edge of longer runs.
On completion, all laps should shed water away from the roof, not towards it, and no joint should allow water to sit. The work should look neat - tight folds, consistent depth in the chase, and a clean mortar finish. Rough edges, visible filler or tape are not hallmarks of a job done correctly.
We carry out lead work across Cambridge and in the surrounding villages. Whether the property has a traditional chimney stack on a Victorian terrace or a flat roof abutment on a modern extension, the principles of correct lead installation are the same.
For most flashing applications on pitched roofs and chimneys, lead remains the best performing material available. It is malleable enough to dress tightly into complex profiles, durable enough to outlast almost any other option, and it is compatible with virtually every roof covering - slate, clay tile, concrete tile, stone. Alternatives such as zinc and copper also perform well and may be specified for particular architectural reasons, but lead is the standard choice for repair and replacement work on most domestic properties.
Single-ply membranes are sometimes used as an alternative at flat roof abutments, but for chimney and dormer flashings, lead is the correct specification on the overwhelming majority of UK homes.
If you have spotted any of the warning signs above - or if you know your lead flashings have not been touched in twenty years or more - call us for a roof survey. We will tell you honestly whether you need a repair, a replacement, or nothing at all.
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Call any time. Calls are answered day and night and passed straight to our roofers.
