If you have a leaking chimney, a weeping valley, or a damp patch spreading from a dormer, the lead flashing is almost always where to look first - and in Sutton Bridge, Downham Market Roofers can assess, repair, or replace it properly.
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Lead flashing is the thin sheet of dressed metal that seals the joint between a roof covering and a vertical surface - the base of a chimney stack, the sides of a dormer window, the angle where two roof slopes meet in a valley, or the point where a roof butts up against a party wall. These joints cannot be sealed with tiles alone. They move with the building and they shed water in a way that rigid materials cannot match.
Properly dressed lead sits in a chase cut into the mortar or masonry, folds down over the tile or slate, and overlaps itself in steps so rainwater always runs away from the building. When it is fitted correctly, it outlasts most other parts of the roof. When it fails - or when it was never fitted correctly - you get water ingress at the most inconvenient and often the most hidden points on the roof.
Lead work carried out to traditional standards uses Code 3, Code 4, or Code 5 lead sheet depending on the location and the exposure of the joint. Code 4 is the most common general-purpose weight for chimney and step flashing. Code 5 is used in higher-exposure positions or wide valley gutters where a heavier sheet is needed.
The most obvious sign is a damp patch on a ceiling directly below a chimney breast, dormer, or valley. However, water travels. By the time a stain appears on a ceiling, the water may have been running inside the roof structure for weeks, finding its level before breaking through plasterboard or lath and plaster.
On the outside, cracked or missing mortar pointing in the flashing chase is a clear warning. Lead that has pulled away from the wall - lifting at its edge - is letting water underneath. Flashing that has slipped downward, lost its step, or been patched with roofing cement is living on borrowed time. Cement repairs to lead joints are a temporary fix at best. The cement shrinks and cracks as the lead moves with temperature changes, and the joint opens again.
Rust staining below a chimney or along a valley line can indicate that the flashing has gone entirely in places and water is reaching the felt or timber underneath. At that point the repair becomes more involved because you may need to look at what the water has done to the roof deck beneath.
This is the question that matters most when you are standing in front of a leaking chimney or a damp dormer. Getting the answer right saves you money. Getting it wrong either leaves the problem unsolved or costs you more than necessary.
The honest answer is that neither repair nor replacement is always the right choice. It depends on the condition and age of the existing lead, the type of failure, the quality of the original installation, and how much of the flashing is still sound.
Lead has a long service life - quality lead flashing, correctly installed, can last 50 to 80 years or more. So if your flashing was installed within the last 20 or 25 years and the failure is localised, a repair is usually the right call. Localised failures include a single section that has pulled away from its chase, one step that has lost its mortar pointing, or a small split caused by foot traffic or falling debris.
Re-pointing the chase is a common and effective repair. The old mortar is raked out, the flashing is pushed back into the chase and clipped, and the joint is re-pointed with an appropriate mix. This is not a job for ordinary pointing mortar, which is too rigid and will crack. A more flexible mix is used so the joint moves with the lead rather than fighting it.
A split or small tear in otherwise sound lead can sometimes be repaired using a lead-bonding solder, though this depends on the size and location of the split. A large split, or one in a position where water pressure builds up, is better addressed by replacing that section. Patching with roofing felt or bitumen tape is not a meaningful repair - it may stop the leak for one winter but it will not hold.
If the flashing has simply lifted because the clips that hold it have corroded or pulled out, re-clipping and re-pointing is a legitimate repair rather than a full replacement. Lead clips are small but critical - they hold the flashing in position without restricting its movement.
Replacement is the right answer when the existing lead is at or past the end of its useful life. Old lead that has become thin through decades of weathering, has multiple cracks, or has been patched so many times that there is more repair than original material is not worth trying to save. You will spend money on a repair and be back on the roof within a few years.
If the existing lead is underweight for its position - Code 3 where Code 4 or 5 should have been used, for example - it will continue to fail regardless of how well it is repaired. Replacing it with the correct weight of lead solves the underlying problem rather than treating the symptoms.
When the original installation was poor - no expansion joints where they are needed, insufficient lap, flashing fixed rigidly rather than clipped - repair work will always be limited by those original shortcomings. A full replacement, done properly this time, gives you a fresh start.
Lead that has crept - slid slowly down the roof face over years - is a sign that the fixings were inadequate from the start. Once lead has crept significantly, the shape of it changes and it no longer sits correctly against the surfaces it is meant to seal. Replacement is almost always the better option in this case.
A full chimney flash replacement on a standard domestic stack typically costs in the region of £400 to £800 depending on the size of the stack and the number of sides that need new lead. Valley replacement costs vary more widely because valley lengths differ, but £300 to £700 is a typical range for a moderate-length valley. These are ballpark figures for the lead work itself and will vary with access, scaffold requirements, and the condition of the surrounding tiles or slates.
Many real jobs fall between the two clear cases. A chimney stack might have sound lead on the front apron and one side, but a back gutter that has given up. In this situation, replacing only the sections that have failed is a practical approach - provided the sections that are being left are genuinely in good condition and not merely surviving for now.
A good roofer will assess the whole flashing before deciding which sections to leave. If there is any doubt about the remaining sections - if they are old, underweight, or showing early signs of the same failure - the cost difference between replacing two sections and replacing the whole stack is rarely large enough to make partial replacement the obvious choice.
Whether you are having a repair or a full replacement, the process of doing it correctly is the same - only the scale changes.
The flashing chase is cleaned out properly. Old mortar is removed, the chase is checked for depth and evenness, and the masonry is sound before anything is fitted. Lead that sits in a shallow or uneven chase will not seal correctly and is more likely to lift.
New lead is cut from a roll to size and dressed - shaped by hand with a dresser and a bossing stick - to fit the profile of the roof and the wall exactly. Dressing takes time and skill. Lead that has simply been bent into approximate shape and pushed against the wall will never sit tightly enough to exclude water over time.
Expansion joints are included at the correct intervals - typically every 1.5 metres for step flashing - so the lead can move with temperature changes without cracking. This is one of the details that separates a job done properly from one done quickly. Without expansion joints, lead in a long run will split along its length within a few years as it expands and contracts through the seasons.
Lead clips hold the flashing in position. They are folded into the flashing itself and fixed to the masonry, allowing the lead to move slightly without being able to pull away or creep downward.
The chase is pointed with a suitable mortar mix once the lead is in position. The pointing is finished flush and slightly angled to shed water away from the joint.
Valley lead is fixed without rigid nailing through the sheet. The lead overlaps at each section, and the overlaps are laid in the direction of water flow.
Before any roofer starts work on your lead flashing, it is worth asking a few practical questions. What code weight of lead are they proposing to use, and why? Where will the expansion joints be? How are they planning to fix the flashing - clips, or nailed through the sheet? Will the chase be re-pointed with a flexible mix or standard mortar?
These questions are not about catching anyone out. They are about confirming that the person doing the work understands the basics of how lead behaves and is planning to carry out the job accordingly. Anyone who cannot answer them straightforwardly is worth thinking twice about.
It is also worth asking whether any surrounding tiles or slates will need to be disturbed, and what condition they are in. Lifting tiles to access a valley or chimney sometimes reveals broken or slipped tiles that were hidden. Addressing those at the same time avoids a second call-out.
Downham Market Roofers carry out lead work across Sutton Bridge and the surrounding area, including in Wisbech, March, and King's Lynn. Whether the job is a straightforward repair to a pulled-away step flashing or a full chimney flash replacement, the approach is the same: assess what is there first, give you a straight answer on whether repair or replacement makes sense, and carry out the work to the standard it needs to last.
If you have a damp patch you cannot account for, or you can see from the ground that something looks wrong around a chimney or dormer, call us to arrange a roof survey.
If you are not sure whether your flashing needs a repair or a full replacement, the best thing is to have it looked at properly from the roof rather than guessing from the ground. Call Downham Market Roofers to book a roof survey and we will give you a clear, honest assessment - what is wrong, what is needed to fix it, and what it is likely to cost.
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