If your roof is leaking around a chimney, dormer or valley and you can't see a broken tile, the lead work is almost certainly where the problem starts.
Lead flashing, valleys and soakers are the parts of a roof that seal the joints between different surfaces. They do a job tiles simply cannot do. When they fail, water finds a way in quickly - and because the entry point is rarely directly above the damp patch inside, the source of the leak can take time to trace.
Knowing the warning signs helps you act before plasterwork, timbers or ceilings suffer serious damage. Below is a practical guide to what to look for, what causes each problem, and when to call a roofer rather than waiting.
A pair of binoculars from ground level will show you a great deal. Look at every point where the roof meets a vertical surface - chimney stacks, dormer cheeks, parapet walls and roof windows. These are the joints that lead is designed to protect.
By the time you can see damp inside, water has usually been entering for some time. The damage visible on a ceiling or wall is nearly always some distance from where the water actually got in, because it tracks along rafters and ceiling joists before dripping through.
Most flashing failures in older properties come down to two things: age and poor original installation. Lead is a long-lived material when it is fitted correctly and to the right thickness, but the failures we see regularly follow predictable patterns.
Thermal movement without proper joints. Lead expands significantly in warm weather and contracts in the cold. A single piece of flashing cut too long without the correct expansion joints - called welted joints or code-appropriate sizing - will eventually buckle, crack or lift. BS EN 12588 sets out the code numbers for lead thickness and the maximum lengths that should be used in each application. Anything longer than those limits without a proper joint is asking for trouble.
Insufficient fixing into the mortar joint. The top edge of a flashing is tucked into a raked-out mortar joint and then pointed back in. If the joint was not raked deep enough, or if cheap ready-mix mortar was used, it can fail within a few winters. The flashing then relies on nothing but gravity to stay in position.
The wrong lead code used for the job. Flashing lead is specified by code number, which relates to its thickness. Code 3 (1.32 mm) is the minimum for most flashings, with code 4 or 5 used in exposed positions or on flat roof details. Using a thinner code than the job demands saves money at the time but leads to premature failure.
Bodged repairs with mortar or sealant. A roofer who runs a bead of silicone or smeers mortar over a failing flashing has not fixed the problem - they have delayed the inevitable while making the eventual proper repair harder and more expensive. Sealants eventually break down, and removing hardened mortar from lead without damaging it takes time.
Galvanic corrosion at contact points. Lead reacts chemically with certain metals. Where lead sits in direct contact with copper - from old copper nails or pipe flashings - both metals can corrode faster than they would alone. This is less common on residential roofs but worth knowing if you have older plumbing vents exiting the roof.
Many properties include a mix of older buildings, bungalows and extensions with lean-to or flat roof details - all of which involve lead work at the junctions. The same warning signs apply regardless of roof type, but the junction between an older main roof and a later extension is a particularly common source of failure where two different materials meet.
Lead work problems do not resolve themselves. A small gap in a flashing joint becomes a larger opening as frost and wind work at it through the winter. If you see any of the signs above, getting a roofer up on the roof to inspect before the next wet season is always cheaper than waiting until water has tracked into the timbers or through a ceiling.
A proper inspection of the lead work on a chimney stack or dormer will tell you whether a section of flashing needs re-pointing, replacing, or whether the entire lead detail needs stripping back and starting again with the correct materials and code.
For any repair to last, the cause of the failure must be addressed - not just the visible symptom. If a flashing has lifted because the mortar joint was too shallow, re-fixing it without raking out a proper chase is pointless. Any lead work should be carried out to BS EN 12588 standards, using the correct code for each application.
Whether the job is a chimney stack with a back gutter, a dormer with step and cover flashings, a tiled valley being replaced with a dressed lead valley, or a soaker replacement at a slate abutment, the approach is the same: strip out the old material, prepare the surfaces properly, form and dress the new lead correctly, and point with an appropriate mortar mix that will move with the building without cracking.
If you have noticed any of the warning signs above - from the ground, in the loft, or on your ceilings - call Brandon Roofers and we will arrange a roof survey. We will tell you exactly what needs doing, in plain terms, before any work starts.
No obligation · We usually respond within 2 hours
Storm damage, active leak, damaged ridge - we aim to be on-site within 24 hours.
